The Zaneveld-Wells technique for determining the inherent optical properties of ocean water is based on calculating the angle-integrated moments of the radiant light field at various depths by an inversion algorithm based on the radiative transfer equation. The hypothesis is that N + 1 sensors can be used to obtain N `inherent optical expansion coefficients,' A_n, from which the single scattering albedo and N-1 expansion coefficients of the volume scattering function can be calculated. We have evaluated the performance and limitations of the proposed algorithm. Results from numerical testing indicate that this technique is a promising way to estimate optical properties of some ocean waters, but attempts to estimate too many expansion coefficients give spurious results for the higher-order coefficients in other cases. Recommendations are given for improving the implementation of the algorithm.

The greatly reduced stratospheric ozone concentrations over the Antarctic continent (popularly known as the Antarctic ozone hole), the consequent increase in short wavelength ultraviolet radiation (UVB), and the influence of this increased UVB on the Antarctic ecosystem has led to the development of new instruments for the measurement of these effects. One instrument, arguably a compromise between a more complex and expensive full spectral narrow-band instrument and a simpler broad-band instrument, is manufactured by Biospherical Instruments (BSI) for the measurement of surface and in-water UV radiation. Here we present preliminary results of direct observations of springtime UVB, using the BSI PUV-510, under the Antarctic ozone hole and provide an algorithm, using the radiative transfer code of Wan, for the accurate estimation of column ozone based upon these measurements. We show that data from the PUV-510 can be used to estimate column ozone, given a rough estimate of surface albedo, to within an accuracy of +/- 10 DU and that this algorithm is robust, working well for both clear and cloudy skies.

The underwater light field is affected by the geometry of the incident radiance, the sea-surface state, the inherent optical properties of the water-column constituents, the distribution of these constituents, and, in shallow areas, the bottom albedo. New instrumentation and platforms designed to assist in the quantification of the above are described. The new instrumentation includes the Marine Aggregated Particle Profiling and Enumerating Rover (MAPPER), the next-generation MAPPER II system, and the Bottom Classification and Albedo Package (BCAP). the new platforms include a custom manufactured remotely operated vehicle (ROV) designed to deploy the MAPPER II module, the BCAP module, and a vertical-profiling instrument suite, and an autonomous underwater vehicle (AUV) designed for optical measurements in coastal waters. These include the deployment of the BCAP module on long- range, bottom-mapping missions.

A prototype in situ multi-sensor fiber optic fluorometer is described which was designed to acquire long term time-series fluorescence measurements. The multi-sensor system uses dual detectors with four excitation sources, thereby providing for independent measurements at eight sensor locations. Strobe excitation light of wavelength < 500 nm is passed through one of each pair of optical fibers and stimulated chlorophyll fluorescence is carried back to a photomultiplier tube. The excitation and detection hardware are enclosed in a pressure case along with a battery operated 500 kHz data acquisition/storage system. Aspects of the design of the fiber optic sensor are described which were intended to optimize detection of fluorescence signals and minimize interference by ambient light. An illustration of the utility of fiber optics for fluorescence measurements was made by comparing a prototype fiber optic profiling fluorometer with a commercial fluorometer. Time series fluorescence measurements were made with the multi-sensor fluorometer in the Gulf of Mexico, and revealed chlorophyll variability in the benthic boundary layer.

In this paper we examine correction methods for the scattering error of reflecting tube absorption meters and spectrophotometers. We model the scattering error of reflecting tube absorption meters for different tube parameters and different inherent optical properties. We show that the only reasonable correction method for an absorption meter without attenuation measurements or a spectrophotometer is the method in which the measured absorption at a wavelength in the near infrared is subtracted. A better correction is obtained if attenuation is measured simultaneously and the absorption at the reference wavelength is multiplied by the ratio of the measured scattering at the measurement wavelength divided by the measured scattering coefficient at the reference wavelength. This is the proportional method. We showed that the important geometrical parameters of the reflecting tube can be obtained by a comparison of measurements and models of polystyrene beads. Finally, we examine the improvements that could be obtained if a direct scattering measurement were made simultaneously with the absorption and attenuation measurements.

An underwater optical serial sectioning system has been developed to measure in-situ three- dimensional distributions of biological particles. The technique involves scanning a thin plane of laser light sequentially through a range of distances parallel to the imaging plane of a digital CCD camera. Images of induced fluorescence in the sequentially illuminated planes are recorded. A computer based inverse program is then used to reconstruct three-dimensional chlorophyll (alpha) distributions from the plane images. The inverse method compensates for attenuation of the fluorescence excitation and emission throughout the volume and converts camera image plane intensity values to mg Chl (alpha) /m³. Graphic display of the composite data set with spatial resolution of 1 cm³ in a 20 X 20 X 20 cm volume is presented in a three-dimensional rendered volume. Chl (alpha) concentration discrimination of 0.1 mg Chl (alpha) /m³ over the range of 0.1 to 2.0 mg Chl (alpha) /m³ has been demonstrated in the laboratory with the optical serial sectioning system.

Phytoplankton spectral absorption of light energy is one of the important factors to estimate primary production of the ocean. We have developed a system which measures in situ spectral absorption of suspended matter, mainly phytoplankton, by a modified opal glass technique. The system was designed to provide sub meter-scale profile of phytoplankton distribution without water sampling. The system consists of a halogen lamp as a white light source, a multi-channel spectrometer and submergible optical sensor unit. The collimating lens and diffuser constitute this unit. The optical fiber cables are employed to transmit the light between the sensor unit and the equipment on shipboard. The received light was measured by spectrometer which ranges from 400 nm to 800 nm with 1024-channel temperature stabilized linear photodiode array. Our preliminary experiment with the cultured phytoplankton (diatoms, flagellate and green algae) has shown that minimum detectable absorption coefficient is 0.01 m^-1.

A submersible absorption meter was built to measure the light absorption plus backscattering coefficients of natural waters in one term. The radiance attenuation is measured close to the surface of a Lambertian light source and it is measured along the direction of the net vector irradiance. Photons scattered out of this normal direction are replaced by photons initially travelling at a deviating direction being scattered into the normal direction. Photons scattered in the backward direction are lost. The performance of the absorption meter was tested in the laboratory working with several simple test suspensions and in the field in estuarine and in marine water. Radiance attenuation spectra of clear water and absorption spectra of clear water matched closely. The radiance attenuation of algae increased linearly with concentration of chlorophyll (alpha) in the measured range of 0 - 70 mg m^-3, while the radiance attenuation spectrum was very close to the absorption spectrum of the algal sample as measured with a semi-integrating sphere. An offset between these spectra remained. This was not observed when field data from estuarine and marine water were compared to laboratory measurements.

A phytoplankton bloom was observed between 67.2 degree(s)S and 68.5 degree(s)S which extended over at least 4 degrees of longitude from 84 degree(s) to 88 degree(s)W in the Bellinghausen Sea. The northern boundary of the bloom was associated with a strong eastward flowing surface jet of low salinity water. The controlling factors for phytoplankton growth were explored by examining north to south transects of surface stability, inorganic nutrients, mean mixed layer irradiance and surface currents. The only parameter found to change along with the phytoplankton biomass was the mean mixed layer irradiance, which approached the light limitation thresholds for Antarctic phytoplankton. A hypothesis to explain the presence of the high concentrations of phytoplankton is a positive feedback mechanism in which the phytoplankton grow well in the low light conditions of the mixed layer. The high concentrations of biomass reduce the light sufficiently to allow low light-adapted phytoplankton flourish, in contrast to the phytoplankton in the clearer waters north and south of the bloom.

Biological and optical measurements were compared during studies in Bedford Basin, Nova Scotia. A principal objective was to evaluate a tethered spectral radiometer buoy, which measured downwelling irradiance at 490 nm and upwelling radiance in wavebands corresponding to the SeaWiFS satellite, along with the fluorescence of chlorophyll (alpha) . Records of upwelling radiance clearly described optical variability in the water. Optical profiles, including diffuse attenuation at 3 wavelengths, detected a subsurface dinoflagellate bloom in August 1993. When the bloom was entrained into surface waters by afternoon winds, the radiometer buoy easily distinguished darker, red water from the background green water. During the study, a red:green radiance ratio and a measure of chlorophyll fluorescence (683 nm: 670 nm radiance ratio) were well correlated with chlorophyll concentration near the surface, whereas green:blue ratios were not. Optical detection of a bloom during its development demonstrates that simple autonomous instruments might be used for detecting some phytoplankton blooms prior to significant environmental impact.

In a recent sea test, measurements of the volume scattering function (VSF) of clear sea water in situ at several angles were made. These measurements used the APL backscattering sensor, which measures the VSF at 170 degree(s); the SRI Beta Pi sensor, which measures the VSF from 179 degree(s) to 180 degree(s); and the SRI backscattering sensor, which measures the VSF at a mean scattering angle of 150 degree(s). The intention of the testing was to quantify the enhanced backscattering feature at 180 degree(s) relative to the scattering at more traditionally measured angles of the VSF. Measurements were made in both clear ocean water and Hawaiian coastal waters. Analysis of the data has been combined with subsequent laboratory instrument intercomparisons to demonstrate that in clear ocean water there is relatively little enhanced backscattering, whereas in more turbid coastal water the feature is pronounced and is clearly higher than the VSF at 170 degree(s). Field data, including vertical profiles of optical backscatter in clear and coastal waters, are shown.

The phytoplankton absorption coefficient is primarily a function of absorption by photosynthetic and photoprotective pigments. Absorption by photosynthetic pigments can be separated from that by other pigments by the former's ability to induce chlorophyll (alpha) (chl (alpha) ) fluorescence. Chl (alpha) fluoresces at wavelengths between 660 and 760 nm with a distinct peak at 683 nm and a broad shoulder near 730 nm. The use of Basic Blue 3 as a quantum counter in spectrofluorimetry allows measurement of chl (alpha) fluorescence at 730 nm and hence, determination of phytoplankton fluorescence excitation spectra between 380 and 700 nm. Extension of measurements beyond 600 nm, the limit of the conventional quantum counter rhodamine B, allows direct comparison of the total absorption spectrum and the fluorescence excitation spectrum between 380 and 700 nm. Errors in the measurement of both types of spectra must be identified and minimized for reliable interpretation of either spectrum. Factors of primary importance include instrument-specific correction spectra for spectrofluorimeter configurations, accuracy in the absorption measurement, and sample handling.

Sea phytoplankton plays a considerable role in the interactive processes between light and the sea. Its species composition and the physiological development phase influence the spectrum of the light attenuation coefficient in the sea. Laboratory measurements of light attenuation spectrum were carried out on three different phytoplankton monocultures of the unicellular green algae Chlorella vulgaris and the larger Chlorella kesleri and the blue-green alga Chroococcus minor. The cultures were subjected to chemical (NaOH and temperature) or physical (ultrasounds) factors which altered their internal cell structures. Distinct changes in the light attenuation spectrum were observed as a result of the modification of the internal cell structures. Light attenuation cross-sections of those phytoplankton cells were also determined.

The analysis of diel variations in fluorescence yield of chlorophyll-(alpha) (Chl-(alpha) ) in vivo is presented in the paper. We rely on recent field observations and laboratory studies, as well as on the biophysical description of the relationship between photosynthesis and Chl- (alpha) fluorescence. The variations in fluorescence yield due to `instant' changes and diurnal variations in ambient irradiance can be explained as the manifestations of `photochemical' and `non-photochemical' quenching of Chl-(alpha) fluorescence, respectively. Field studies of the diel variability in Chl-(alpha) fluorescence were carried out with a shipborne lidar system in the Baltic, Mediterranean, and Black Seas, and in the Atlantic Ocean. As predicted by the model, we observed the maximal values of Chl-(alpha) fluorescence yield in the near-surface layer at night and its decrease in the noon. The max/min ratio varied from 3 to 1, depending on environmental conditions and, thus, on the functional state of photosynthetic apparatus. Non-photochemical mechanisms of `photoinhibitory' and energy-dependent quenching were found to be the major mechanisms of regulation of Chl-(alpha) fluorescence yield at a diurnal scale.

Although nutrient-limited growth of phytoplankton in the laboratory produces well-defined responses in the absorption coefficient, pigmentation, and quantum yield of photosynthesis, natural populations show only weak or inconclusive effects. Further analysis of the data from Biowatt-II, a seasonal study in the NW Atlantic in 1987, suggests two things. First, the phytoplankton absorption coefficient changes as a function of chlorophyll (alpha) , although photoprotectant accessory pigments are important in summer. Second, with the exception of one cruise, the data suggest that an estimated maximum quantum yield varies by less than 20%. Resolution of the issue of a nutrient effect may come with detailed measurements in a tropical region, in an ocean province without seasonally varying irradiance but having a strong seasonal signal in nutrient concentrations.

We have developed a bio-optical profile model which attempts to predict the vertical distribution of chlorophyll and the coefficients for diffuse downwelling irradiance attenuation and beam attenuation from measurements at the sea surface. In this paper we test the ability of this model to `fit' the vertical profiles measured at 117 stations in the North Atlantic. In general predicted values for the vertical distribution of chlorophyll and the beam attenuation coefficient fall within about 35% of measured values. In order to understand the pattern of distribution for the 7 tuning coefficients, we have calculated the principle components for the 7 X 117 matrix of `best-fit' values for the tuning coefficients. Such a calculation indicated that covariance among the 7 tuning coefficients was limited. It also indicated that variation in the scores for the dominant principle components were strongly dependent on the temperature at the sea surface and weakly dependent upon the concentration of chlorophyll at the sea surface. Finally, the relationship between the scores of principle components and the temperature-chlorophyll axes may provide a means of extrapolating the bio-optical profile model in time and space.

The optical properties of pure water are basic input data for many geophysical investigations such as remote sensing of surface water and underwater radiative transfer calculations. Knowledge of the spectral properties of components in surface water is required for accurate interpretation of measured reflection and attenuation spectra in terms of their concentrations. Also the sources and sizes of errors in the basic data must be known. Absorption measurements were done with a submersible absorption meter in the temperature range 2.5 till 40.5 degree(s)C. The scattering of pure water is recalculated using the Einstein-Smoluchowski equation. The input for this equation is evaluated and the temperature dependency is included. New values for the absorption coefficient are given based on these results and analysis of data from the literature. Absorption in the wavelength range 300 - 550 nm is lower than presently used values. In the wavelength range about 700 nm the spectrum has a different shape. A formulation of the effect of temperature on the absorption spectrum is given.

Inherent and apparent optical properties as measured in case 1 waters often deviate in seemingly random ways from values predicted by bio-optical models that parameterize the microbial composition of the water in terms of the chlorophyll concentration alone. We believe that this `random' variability in optical properties can be explained in terms of variability in the detailed microbial composition of the water, and we outline a research program for testing this hypothesis. Our approach combines laboratory experiments on monospecific microbial cultures, Mie scattering calculations, and radiative transfer numerical modeling. This approach also provides a unique means for improving bio-optical models and for developing new optical methods or algorithms for the study of biological processes in the upper ocean. We present here a few examples from preliminary results of this work. These examples show selected measures of the underwater light field for a hypothetical ocean that consists of pure water, viruses, heterotrophic bacteria, cyanobacteria, and small diatoms as optically significant components.

Using a modified form of the anomalous diffraction approximation we have been able to derive in closed form an analytic expression for the phase function of Mie scatterers integrated over an inverse power law (Junge) size distribution. The analysis explains the apparent singularity seen experimentally at the forward scattering angle. Simple relationships are also derived that relate the inverse power law as a function of scattering angle in the near forward direction to the power law of the size distribution. The parameters of the formula are the relative index of refraction and the inverse power of the size distribution. A comparison is given between the analytic formula and exact integration of the Mie scattering for spheres. This new phase function is used in the analysis of forward angle transmissometer- nephelometer data collected by DREV in the Arctic, Atlantic, and Pacific.

The backscattering coefficient of the marine hydrosol is recognized as an important optical parameter to extract from the radiance and irradiance data of the hydrosol. One of the more promising algorithms for extracting this parameter, utilizing remotely sensed reflectance, has been proposed by Zaneveld. We have studied the implications of the simplified algorithm with the Naval Research Lab (NRL) optical model, a Monte Carlo simulation of the radiative transfer equation using standard absorption and elastic scattering coefficients for the water molecule, organic matter, and minerogenic matter. The known inputs of inherent optical properties can be used with the radiant flux outputs to check and verify algorithms that invert the measured irradiance streams for inherent optical properties. The results indicate that the inversion of the backscattering coefficient from remotely sensed reflectance is in error in the range of a 40% overestimate to a 10% underestimate of this parameter. The errors are dependent on both the solar angle and the constituents contributing to backscattering. Knowledge about the general shape of the backscattering function of a given hydrosol is necessary for the most successful inversion algorithms.

The goal of this work is to verify different spectral models of the diffuse attenuation and absorption coefficients of sea water and to work out a recommendation for their use. It is shown that the spectral models of the diffuse attenuation coefficient K_d((lambda) ) developed by Austin, Petzold, 1984 and by Volynsky, Sud'bin, 1992 correspond with each other, as well the models of Ivanov, Shemshura, 1973 and of Kopelevich, Shemshura, 1988 for calculation of the spectral absorption coefficient a((lambda) ) on the values of K_d((lambda) ). Theoretical foundation of the relation between a((lambda) ) and K_d((lambda) ) is given. The up-to-date physical model of the sea water light absorption is considered and checked by means of comparison with measured values of the attenuation coefficient at the ultraviolet and visible spectral ranges.

We have developed a Monte Carlo program to calculate the complete four component Stokes vector for a coupled atmosphere-ocean system which also includes Raman scattering as well as a stochastic interface. Since the input to this program requires Mueller matrices for all scattering processes as well as the interface we had to derive the correct Mueller matrices for both Raman and elastic fluctuation scattering. We were then able to calculate the radiance, degree of polarization, orientation of the polarization ellipse, and the ellipticity of the radiation field at various levels within the ocean as well as just above the ocean surface. We found that the effect of Raman scattering on the polarization of the light field within the ocean is significant and can be detected by making polarimetric measurements within the ocean.

Pulse broadening due to multiple scattering has long been of fundamental importance in the study of laser pulse transmission through the ocean as well as other diverse areas of science such as astrophysics, meteorology, and medical physics. We have used a Monte Carlo simulation to investigate the spatial and temporal spreading of a pulse (`pulse stretching') as it propagates through a medium due to small angle multiple scattering as described by van de Hulst and Kattawar. We show the transformation of single scatter distributions into those predicted by the central limit theorem. We also derive the scattering property of the medium finding a simple relation between the phase function and the scattering parameter which connects the single scatter mean square scattering angle, <(Theta) ²>, and the multiple scatter expectation value, <(Theta) ²>, along with well defined limits of validity of the present theory in terms of the basic scattering parameters of the medium.

Light scattering induced by turbulent flow in seawater has been studied and the effect of seawater turbulence on the propagation of a collimated light beam has been characterized. Our approach is to describe the interaction of light with inhomogeneities in the refractive index (IRI) by solving Maxwell's equations. This set of equations is converted into the parabolized Helmholtz equation in the case of light propagating through water with IRI. We characterize the light scattering within a water parcel by the volume scattering function (VSF). Field measurements of small-angle VSF exhibit a sharp peak which is orders of magnitude greater than that obtained from either laboratory measurements or Mie calculations for suspended particles. Our computer simulations show that the volume scattering function obtained is indeed characterized by an exponential decrease with scattering angle and is in quantitative agreement with in situ observations in the case of high temperature variance dissipation, (chi) . It appears that 0(1 degree(s)) is the upper limit of turbulent induced light scattering in the ocean.

We have shown in an earlier paper that by measuring the decay of the irradiance field due to a point source, the absorption coefficient of the medium can be determined. A central parameter in this method is the average cosine of the radiance distribution at each measurement point. From measurements of the point spread function (PSF), an estimate of the average cosine can be determined. However, experimentally the PSF is routinely measured only to 12 degrees. We have also previously shown a method which relates the small angle PSF measurements to an empirically derived analytic formulation of the beam spread function (BSF) which extends to 90 degrees. We present an independent test of this method, and then use the BSF to determine the average cosine for varying ranges (from the point source) and water properties. In this way we can estimate how rapidly the average cosine varies, and its relative importance in the field measurements of the absorption coefficient with these techniques.

Diffuse attenuation coefficients for spectral irradiance K_d((Zeta) (lambda) ) and the total Chl (alpha) + Pheo (alpha) pigment-specific absorption of light by particles ((alpha) _p^*((lambda) ), algae + detritus), were determined during two cruises (Cardeep 2 and 3) in the Greenland/Iceland/Norwegian (GIN)-Seas. The pigment (Chl (alpha) + Pheo (alpha) ) specific attenuation coefficient K_d^*((lambda) ) was compared with Morel's non-linear model for light propagation of solar energy in the ocean and with the pigment specific absorption coefficient by particles, (alpha) _p^*. Our K_d^*((lambda) ) spectrum for the GIN-Seas was in good agreement with values derived from Morel's model for pigment specific light attenuation for 1 mg (Chl (alpha) + Pheo (alpha) ) m^-3 for wavelengths in the blue part of the spectrum. K_d^*((lambda) ) (apparent optical property) and a_p^*((lambda) ) (inherent optical property), were in good agreement except at wavelengths > 665 and < 441 nm. This was only true for the (alpha) _p^*((lambda) ) spectra for which the optical density from 750 - 800 nm was not subtracted.

In this study we propose a model of phytoplankton population dynamics in a marine ecosystem which include physical, biological, and bio-optical parts. We discuss two different methods of contact chlorophyll observation assimilation to fit a model of `in situ' data. As an example we simulate the abnormal 1993 Gulf of Gdansk spring bloom during which extremely high chlorophyll concentration were observed. The data assimilation approach serves as a basis for more adequate underwater light field simulations.

The photochemical effect of solar ultraviolet radiation on colored dissolved organic matter has been recently revealed. This effect consists in the change of spectral absorption of sea water in the UV band. In the present paper the experimental data are parameterized to include this effect into radiative transfer theory. A radiative transfer model is developed for calculation of the spectral UV flux at different depths in the sea. The resulting nonlinear radiative transfer equation is solved by the consequent iteration method using quasi-single scattering approximation. Calculations of the spectral irradiance within 290 - 400 nm band were carried out for different solar zenith angles and for different total amounts of ozone. A model of spectral optical properties of sea water inherent to the coastal zone was used. By convolution of irradiance spectra with the DNA action spectrum the biologically effective UV dose rates were calculated. It is shown that solar UV-light effect on the colored dissolved organic matter absorption leads to about 40% increase of the DNA dose rates at a depth of 4 m.

Calculations of self-shading for an instrument measuring upward irradiance were conducted with a Monte-Carlo radiance transfer algorithm. The algorithm included Cox-Munk wave- slope probability function and simulation of diffusion on sea-bottom allowing incorporation of rough and/or shallow sea in the simulations. The effect of the self-shading phenomenon was calculated in the function of instrument radius, sea-water absorption, surface roughness (depending on assumed wind velocity up to 15 m/s) depth of the instrument, its height over bottom and bottom albedo (both diffusive and reflective one).

Profiles of spectral attenuation and absorption were measured in situ with a WET Labs AC-9; scattering coefficients were calculated by difference. Closure of the absorption and scattering coefficients was obtained on this limited data set for in situ and discrete sample measurements. Centimeter-scale fine structures were observed in the vertical profiles. Total absorption coefficients were dominated by the phytoplankton component. Total attenuation coefficients were dominated by scattering although the effects of strong absorption were apparent in both the attenuation and scattering spectra. The vertical structure of absorption and scattering were not spatially coherent, nor were the vertical structures of phytoplankton and non- phytoplankton absorption. The strongest spatial coherence was observed between the non- phytoplanktonic component absorption and particle scattering coefficients. The spectral absorption coefficients of the in situ phytoplankton component exhibited decreasing blue to red absorption ratios as a function of depth and spectral flattening of the blue absorption peak indicative of photoadaptation.

A model has been developed to investigate the influence of the subsurface chlorophyll profile on the complete spectral water-leaving radiance (ocean color) from 400 - 700 nm. The spectral reflectivity of vertical chlorophyll layers is modeled and coupled with the spectral incident irradiance at the sea surface. Model results indicate similar water-leaving radiance signatures can be obtained from different subsurface chlorophyll profiles. This model provides an interpretation of remote sensing ocean color signatures and possible subsurface structure. The inherent optical properties of the backscatter and absorption coefficient which are determined from the vertical chlorophyll profile for Case I waters are used to calculate the subsurface spectral reflectivity at layer depths. Subsurface reflectivity models are coupled with an atmospheric model of the incident solar irradiance spectrum. The atmospheric irradiance model was run for different cloud cover and different optical depths (ozone, aerosol). The coupled model results compute the remote sensing color spectrum (upwelling radiance) at the sea surface.

In the turbid and yellow substance rich waters of the outer Oslofjord the turbidity and the Secchi disk depth have been successfully determined by remote sensing, with the TM channels of Landsat 5. Similar attempts to determine the total suspended matter and the beam attenuation coefficient at 520 nm have been less successful, and the content of chlorophyll- (alpha) is the most difficult to estimate, if at all possible with this sensor. Observations in the green and red parts of the spectrum give the best correlation. The method requires that a few field measurements and samples are taken, and the constants of the algorithms will vary from case to case. These results and the possible causes of the variation are discussed. Established optical theory for the backscattering of light from the sea to the atmosphere is tested by optical measurements. The results indicate that the ratio between the radiance from nadir in the sea and the downward irradiance may have a significant variation in these coastal waters that we so far are not able to predict.

An iterative technique has been developed to improve coastal zone color scanner (CZCS) estimates of upwelled subsurface water radiances (L_u) in Case II waters. Regional relationships between the diffuse attenuation coefficient measured at 490 nm (K490) and L_u measured at 443, 520, and 550 nm were developed using data collected in the northern Gulf of Mexico in April 1993. These relationships are used to iteratively adjust the aerosol contribution to the total radiance measured at the sensor. The open-ocean assumption that there is no water-leaving radiance at 670 nm is not valid in coastal areas with a high sediment load. If the sediment signal is not considered the aerosol contribution is overestimated during the atmospheric correction of the CZCS data. Subsequently, the calculations of L_u are underestimated, even to the point of negative radiances calculated in extremely turbid areas. Because the L_u are used in the geophysical algorithms to estimate K490 and pigment concentration, these derived products are overestimated in Case II waters if the 670 nm radiance is not partitioned into aerosol and sediment components.

The Kattegat region forms a transition zone between the Baltic Sea and the North Sea. Baltic Sea water being brackish and high in yellow substance mixes with saline and dense North Sea water which is either low or high in yellow substance. Yellow substance combined with salinity is most suitable for water mass classification in the region since the Baltic water is characterized by a low salinity in combination with a high yellow substance content, whereas the North Sea water originates either from the Atlantic having extremely high salinities and low yellow substance content or from the German Bight which has an intermediate to high salinity and a very high yellow substance content exceeding the one in the Baltic proper. Measurements of salinity and yellow substance in the Kattegat allow the construction of a yellow substance/salinity diagram which serves the same purposes as the classical temperature/salinity diagram where the latter is not applicable in coastal areas. The yellow substance/salinity diagrams also permit discoloration studies resulting from mixing of Case 1 waters and Case 2 waters rich in yellow substance.

Imagery and digital tapes (CCT) from ERS-1 and Landsat, regarding the Black Sea coastal zone of Romania have been analyzed with special emphasis on turbidity, current circulation, waste disposal plumes, and convergent boundaries between different water masses. Landsat image radiances were correlated with `in-situ' measurements of suspended sediment concentration. Color density slicing helped delineate the suspended sediment patterns more clearly and differentiate turbidity levels. A good correlation was found using sediment concentrations as a function of depth, since the bands penetrate different depths, ranging from several meters to several centimeters, respectively. The wind speed dependence of the microwave brightness temperature of the sea is interpreted primarily for small scale wave structure at wind speeds below 10 m/s and from increasing coverage of sea foam at higher wind speeds.

Accurate characterization of dissolved organic matter (DOM) optical properties is crucial for accurate measurement of chlorophyll from remotely sensed color data and for modelling spectral light penetration in the ocean. In coastal areas, changes in the humic acid: fulvic acid ratio of gelbstoff from riverine to marine environments cause significant changes in the spectral slope parameter but are difficult to predict a priori and impossible to measure without extracting gelbstoff from seawater. Our recent results from a wide variety of natural waters show that DOM optical properties are a function of physical, chemical, and biological processes. Detailed fluorescence spectroscopy shows changes in the optical properties of gelbstoff related to the onset of marine productivity in coastal transition zones which are indicative of changes in chemical composition of DOM. In this paper, we discuss our efforts to use fluorescence to aid interpretation of variability in gelbstoff spectral slopes for development of next generation chlorophyll algorithms and for development of an optical tracer of geochemical processes involving dissolved organic carbon.

In Sweden work on airborne depth sounding lidar has taken place for more than ten years. Activities include the development of a helicopter borne lidar called FLASH as well as instrumentation (HOSS) for in situ measurement of the optical water parameters. These instruments have been used in rather extensive field trials some of which are discussed in more detail. Recently we have been engaged in analysis of lidar data to determine system performance and possible ways to optimize that relation to lidar parameters and anticipated bottom depth and topography. Examples from that analysis are presented. Comparisons between laser and acoustic soundings are presented. The FLASH system has been further developed into two operational systems called Hawk Eye with Saab Instruments as the main contractor and Optech Inc. as the main subcontractor. The first of these two systems has now been delivered for helicopter installation and acceptance flights. Data from Hawk Eye is discussed.

Two years ago we designed, built, and tested a ROV mounted range-gated imaging system. Given that the target covers at least one pixel at the maximum range of interest the model predicts that for the same laser power and under the condition where the field of illumination is matched to the field of view there is no performance penalty in increasing the field of view. In order to test this result we have built and deployed a second generation underwater imaging system whose field of view and field of illumination are matched and continuously variable from 60 mr to 600 mr in water. The laser source was also upgraded in power by a factor of 10 to a water cooled, 2-kHz, 400 mw doubled Nd:YLF laser. The light is collected by a 7-cm diameter zoom lens. The detector is a gated image intensifier with a 7-ns gate and a gain which is continuously variable from 500 to 1,000,000. An on-board image processor has been added to the system. It allows us to frame integrate in real-time and thus further improve system performance.

In this application of LIDAR (light detection and ranging), the times of flight for signals detected from the reflection of the light pulse off the air/water `surface' interface and off the sea bottom are converted into slant range distances from which the water depth can be determined. The SHOALS system records data for three independent channels which contain surface information. Two of these, the infrared, which is effectively an interface return, and Raman, which is strictly a volume return, are used singly or in concert to ensure that these goals are met. Results from the green channel are ambiguous due to the uncertain nature of the origin of that energy, and are not used. Field test results indicate that easily detectable returns were received in both infrared and Raman channels under virtually all test conditions. The use of independent surface channels also permits operation at extremely shallow depths. Excellent delineation of tidal erosion `cuts' through nearly exposed `mud banks' was obtained in Florida Bay for use in flow modeling programs.

The present work consists of two parts. In the first part, the principal results of the scattering theory of ultra short light pulses (USLP) by a small spherical particle are briefly outlined. In the second part, the peculiarities of the USLP scattering by marine suspension are examined.

To study the influence of sea-perturbations on an optical wavefront in coherent detection through the air-sea interface, we have used two experimental methods based on interferometric techniques. We use Michelson interferometry and Fourier transform to determine wavefronts deformations after double passage through a wavy air-water interface. We consider the statistical aspect by using the averaged Fourier spectra over many independent realizations. Then, a spatial coherence analysis of light scattering in turbid water is presented: the module of the degree of spatial coherence across the beam section is measured by a Mach-Zehnder interferometer.

The results of theoretical study of the problem of detectability of vertical profiles of hydro- optical characteristics in sea water column with the help of airborne lidars are presented. The approach used is based on the developed theory of retroreflected light pulse formation in scattering medium with angular anisotropy of volume scattering function and Sakett's discriminability criterion; the effects of solar illumination, sea surface waves, and atmospheric backscattering are taken into account, as well as the internal noise factors of lidar transmitter and receiver. The recommendations are formulated for system parameters optimization for separate subsurface water layers detecting in various hydro-optical situations and different environmental conditions.

A new theoretical approach is suggested for the problem of backscattered light signal kinetics under the pulsed illumination of sea water column. The developed model uses the small-angle- scattering approximation for the sounding and backscattered light beams and takes into account the angular anisotropy of volume scattering function (VSF) in the back hemisphere. The predictions of the theory are supported by the results of laboratory experiments with model scattering media. On the basis of the model, an interpretation is proposed for some anomalies in the shape of lidar signals registered in airborne sounding experiments. The interpretation of the effect of `enhanced backscattering' from separate sea water layers is shown to be consistent with the recent unique measurements of VSF in the vicinity of 180 degree(s) and revealed fine structure of vertical profiles of the backscattering coefficient. The physical nature of the effect is discussed.

A Monte Carlo model is used to examine the effect of water turbidity on the temporal storage of photons. Multiple scattering can store light in increasing scattering orders. It is hypothesized that this light will be present in a LIDAR gate when signal photons return from a distant target and will generally exceed the backscatter predicted by single scatter models. A photon's mean survival time in a turbid medium is the product of the medium's absorption coefficient at the photon's wavelength times the speed of light in the medium. For very clear ocean water this is about 190 nanoseconds. The model considers an unbounded body of water illuminated by light from a pulsed laser beam. An irradiance receiver collocated with the laser transmitter is the detector. Storage is studied as the absorption and scattering constituents of the water are incrementally varied in multiples of those found in clearest sea water. Single scatter albedos ranged from about 0.2 to 0.85 to span naturally occurring conditions. Results for this geometry show multiply scattered light surpassing singly scattered light returns for paths of the order of a volume attenuation length or less.

In recent years, broad area imaging lidar systems have been applied for ocean applications. These lidar have now been operated in the field since 1988. These systems possess certain intrinsic advantages over narrow angle systems, and can measure, while deployed, the very oceanographic properties on which their performance depends.

A Sea Tech single wavelength (488 nm) absorption meter (known as the `a-meter') has been deployed in the Florida Straits and in the open ocean near Kauai, Hawaii. The instrument has been evaluated to assess its performance in measuring the diffuse attenuation coefficient (K_d) so that the numerous problems associated with traditional K_d measurements can be avoided. (Traditionally, one measures downwelling irradiance, which requires daylight and suffers from the effects of clouds, ship shadowing, instrument tilting, surface wave focussing, and Raman transpectral scattering.) The main result of this evaluation is that the a-meter generally provided profiles that agreed with traditional K_d profiles to within about 0.003/m, and the instrument did not suffer from any of the problems of irradiance measurements. It did, however, require the use of knowledgeable deployment, maintenance, and calibration techniques and the use of essential supporting measurements in order to obtain this degree of accuracy. This paper describes these aspects of how to effectively use the a- meter and provides representative examples of simultaneous traditional K_d profiles.

Biogenically produced calcite represents a significant source of light scatter in the ocean, poorly defined in space and time. We describe an automated photometer for measuring 90 degree(s) light scatter due to calcite on time scales as short as a minute. Raw seawater continuously flows through a 1 mL glass cuvette illuminated by a helium-neon laser. A photodiode is used to measure the 90 degree(s) light scatter of particles in the incident beam. During each sampling interval, a calibrated addition of weak acid lowers the seawater pH to dissolve the calcite and another 90 degree(s) light scatter measurement is made. Standard curves are prepared using calcium carbonate coccoliths from the coccolithophore Emiliania huxleyi. The relationships between acid-liable light scatter and coccolith abundance given an r² of 0.96 - 0.99. The light scatter photometer is coupled to a fluorometer, temperature and salinity probe to relate the suspended calcite concentration to algal distributions and hydrography. We show some examples of its performance at sea.

A new method of measuring the total scattering coefficient b of turbid water is described. The method is based on measuring the irradiance and radiance from a point isotropic source. It is shown that the method accuracy can be improved by using the empirical relations between b and some integral parameters of the scattering phase function. A simple scattering meter `Turbido' based on this method has been designed, patented, calibrated, and tested. The instrument is intended for in situ measurements of b and concentration of suspended particles C in tap and natural waters. In the red spectral region the measurement range of b is 0.18 - 18 m^-1, C ranges from 0.3 to 30 mg/l. The advantage of the instrument compared with nephelometers is its simplicity and weaker dependence of its readings on sizes of suspended particles.

The light field in reflective tube type absorption meters was modeled with Monte Carlo methods. The entrance light field was varied and the systems geometry was varied together with the inherent properties of a test medium. This enabled us to calculate the radiance attenuation as a function of the field of view for several variants of a reflective tube absorption meter. It was found that an instrument with a Lambertian entrance light field and a small field of view measures the sum of absorption and backscattering with an error less than 2 - 5%. This result is independent of the shape of volume scatter functions for surface water. For small fields of view the reflectivity of the cylinder was found not to be critical.

The shear volume of profiling spectroradiometer data is increasing dramatically as global change research programs are placing more emphasis on the evaluation of spatial and temporal structure of ocean biogeochemical cycles. These vast amounts of data must be calibrated, processed, reduced, analyzed, and interpreted in a timely manner. Here, we present a computer data processing for efficiently achieving this goal, in terms of both computational and human resources. The processing system is comprised of a suite of ANSI C++ programs that read and operate on a specified file format, the lowest common denominator (LCD) data file. The LCD file contains all relevant data and metadata in a single ASCII file. UNIX shell scripts are used in the control of data flow as well as error and log handling. The final product is a binned spectroradiometer data set with relevant derived parameters included that may be disseminated to other groups or data bases. At UCSB, we have been using the BBOP system for the past two years and the system is available for use by other research groups.

A laser-based illumination system that can be incorporated into the existing underwater viewing system of current remotely operated vehicles (ROVs) has been investigated. A stripe of projected laser light is scanned over the target and resultant image frames are processed and combined to produce a computer generated composite image. Initially, the system was characterized through trials in the underwater optical test facility at Cranfield where water conditions are easily controlled. Subsequently, further work was carried out on a self- contained underwater unit at a flooded quarry in Leicestershire. Several advantages of this technique have been identified from the laboratory and field trials. Scanning the laser source allows greater control of the lighting envelope resulting in more optically uniform images. Contrast improvements of 300% and range improvements of 50% over orthodox systems have been measured. The use of image processing allows a greater degree of flexibility in image presentation and because this methodology is based on a standard underwater camera, it is complementary and can be fitted retrospectively at relatively low cost.

The small angle volume scattering function (SAVSF) of seawater is one of the most important ocean optical parameters, which influences the laser beam propagation and the underwater image properties, so the in situ data of SAVSF have a great importance in ocean optics and in many applications. We have built a new type of scatterometer for measuring the SAVSF of seawater. The instrument uses an underwater imaging system to measure the optical transfer function (OTF) of the seawater body, then the SAVSF can be calculated. The configuration of the scatterometer is presented and the main performance is analyzed. The results of in situ experiments in the East China Sea are also presented.

The small angle scattering function of seawater (SASF) is a significant parameter of ocean optics, and has an important role on the underwater transmission of image and narrow beam. In this paper, we have described the image transmission method of measuring SASF and the system which we have set up for measuring SASF by the method. We have collected a lot of data using the experiment system with different water path range. The measurement results agree with the theory.

Because of the scatterance of water, underwater image is deteriorated. It is necessary to restore the image for underwater photography and underwater robot vision. In this paper, we have simulated the process of the image blurred under the water, described the steps of de- blurring the underwater image using Monte Carlo method, and restored the blurred image in the different random noise by this method. The results of restoration are satisfactory.

An extensive database of the optical properties of the ocean has been established. The phase function data has been analyzed using a modified form of the anomalous diffraction approximation. Results are presented for the fitted values of the index of refraction, inverse power of the size distribution, total scattering, forward to backward scattering ratio, backscatter, mean cosine and second moment of the scattering distribution. The size distribution database has been analyzed using a new algorithm which allows the size distribution to be decomposed in a set of zero order log-normal distributions. The data is presented both in terms of the standard parameters of the log-normal and in terms of total integrated component amplitude, mode location, and half width. This latter form is relatively independent of the model distribution used. Statistical correlations between the various parameters are given. We have found that the database defines a working envelope of optical parameters that should be useful to the designer of underwater optics.

We have studied temperature dependent changes of the absorption coefficient of pure water at several wavelength bands in the visible portion of the spectrum. A WET Labs Inc. nine wavelength absorption and attenuation meter (AC-9) was used to measure the absorption coefficient. We found the largest temperature dependence (0.0034 m^-1 degree(s)C^-1) at the longest wavelength tested (715 nm). The temperature dependence at shorter wavelengths was less than a third of that observed at 715 nm. Because of the experimental arrangement we believe that the figures obtained represent the upper bound of possible values for the temperature dependence of the absorption coefficient.

A method for detection and estimation of the parameters of jump-like changes of the expectation of optical data for ocean/sea investigations, based on changes approximations by cumulative distribution functions, is proposed. Algorithms and programs for the change-points detection and estimation of the expectation of a stochastic process, based on approximations of the changes by cumulative distribution functions, are constructed and tested.

The paper deals with some aspects of the underwater imaging theory. The first effect discussed is the increasing of sighting range of sea bottom with an observer's altitude over the sea surface. Calculations show that the maximal sighting range from the space under the most favorable conditions does not exceed 500 meters. Secondly, the dependence of the sighting range and the resolution on size of target elements and target itself is considered. It is shown that the apparent contrast of target elements equal in size is higher for smaller targets. Computations prove the nonmonotone dependence of contrast on distance between the observer and the target. Finally, we consider the possibility of observation of the ocean bottom in coastal waters through clouds and show that large details of the bottom, such as sand spots against the seaweeds background, can be seen through continuous clouds with an optical thickness under 10.

The consequences of light scattering from both spherical and non-spherical particles on the propagation of light in the ocean were investigated. The scattering from an ensemble of non- spherical micro-organisms is calculated using the coupled-dipole approximation with an orientational average over Euler angles using Gauss-Legendre integration. Mie calculations provide rigorous solutions for spherical particles and are considerably less computer intensive than the coupled-dipole approximation. Furthermore, they have been shown to accurately predict the scattering for marine organisms that are nearly spherical. Scattering matrix elements calculated using the coupled-dipole approximation were compared with those obtained using Mie calculations in the limit as an ellipsoidal object approaches a sphere in order to assess the limits of applicability of the Mie theory to ellipsoidal particles. Experimental measurements of the scattering matrix elements for spherical particles (latex spheres) and ellipsoidal particles (Bacillus subtilis) were used to test the validity of our analytical approach.

The specific goal of this work is to develop a model and algorithms of using the optical remote sensing and/or the Secchi disk depth data for an assessment of sea water optical characteristics up to 200 m taking into account the vertical stratification. Measurement data of the scattering coefficient b(550) and of the volume scattering function at 1 degree(s), 6 degree(s), 45 degree(s) angles at 550 nm as well as of the absorption coefficient a(390), a(430) at 390 and 430 nm in the Atlantic, Pacific and Indian Oceans were grouped at five layers and were statistically analyzed. Relative standard errors of the a(390), a(430), b(550) values being calculated for deeper layers by their values at 0 - 10 m layer are estimated as 12 - 35%. A model is also developed to estimate the values of the scattering coefficient in the upper 200 m through the Secchi disk depth; the values of the volume scattering function for different layers can be assessed by using the mean scattering phase functions calculated for clear and turbid waters. The spectral absorption coefficients in the upper 200 m can be evaluated in principle by values of the diffuse coefficient K_D(490) at 0 - 10 m layer.

Statistical analysis was applied for the study of vertical profiles of beam attenuation coefficient C(z) and temperature T(z) measured in the North Atlantic in September 1988. The following statistical parameters were calculated: correlation and covariance matrices, eigenvalues and eigenvectors, and factor loading. The correlation matrix for profiles of beam attenuation coefficient differs from the temperature one. The latter characterizes by high correlation at all depths (10 - 130 m). For profiles of beam attenuation coefficient correlation is high only at vertical separation less than 30 - 40 m. The cumulative percent of total variance explained by the first few eigenvectors and corresponding standard errors of eigenvector representation of observed profiles were calculated. The first factor loading for beam attenuation coefficient is maximum at depths less than 30 m. The second factor loading is maximum at a depth of 50 m where in many cases the nepheloid layer is observed. The study of statistical connection between temperature and beam attenuation coefficient vertical profiles shows that correlation between the first principal components C and T is sufficiently high. For the other principal components C and T correlation is close to zero.

In July-August 1988 optical measurements in the Northwest African upwelling region were carried out. Measurements of vertical profiles of beam attenuation coefficient C(z), diffuse attenuation coefficient K_d, temperature and salinity were made at 39 stations during 9 days. In addition, continuous measurements of chlorophyll fluorescence and surface temperature were carried out between stations. Observations showed very high spatial variability of optical properties in the study area. For instance, surface value of beam attenuation coefficient at wavelength 530 nm varied from 0.15 m^-1 to 2.6 m ^-1. In the central part of the study area the filament of relatively cold (temperature about 18 degree(s)) and transparent water (value of beam attenuation coefficient less than 0.6 m^-1) was observed. This filament was oriented perpendicularly to the coastline, its width was 30 - 35 km near the shore and 10 - 15 km at 18 degree(s) W. The filament was separated from surrounding waters by frontal zones where value of optical properties increased sharply. Most turbid waters were observed in the southwestern corner of the study area and most transparent in the northeastern corner.

When working with moderate bandwidth radiometers in regions of the solar spectrum with large variations in intensity as a function of wavelength, significant errors can be introduced from the difference between the lamp spectrum and the solar spectrum. Under these conditions, a `perfect' radiometer can grossly over- or under-estimate the solar irradiance, while several otherwise identical radiometers with center bandwidths ranging over +/- 2 nm can report significantly different irradiances. A direct instrument intercomparison experiment was conducted in San Diego, Calif. using 15 five-channel filter radiometers. The instruments were operated for approximately one week alongside a 0.7 nm bandwidth scanning spectroradiometer under a variety of solar conditions. All of these instruments had been calibrated with lamp standards traceable to NIST. In an effort to reduce the uncertainties of transferring calibration made with standard lamps to filter-based radiometers, we suggested that `source-specific' calibration constants, referenced to both lamps and reference solar spectra, be used. This investigation explores how well this procedure can work, and contrasts this result with intercomparison- and regression-based calibrations.

An accurate knowledge about the spatial distribution of infrared radiation near the sea line is very important as background when designing remote sensing or marine traffic surveillance systems with infrared radiation for use from the shore or ships. For this purpose, the distribution of infrared radiation from the sky and the sea surface near the sea line was measured with an IR radiometer and an IR scanner. Further, spatial distribution characteristics of infrared radiation were studied on meteorological models. As a result, it was confirmed that there is a high radiance zone of mid infrared region (8 - 13 micrometers ) near the sea line. This was also confirmed by a simulation that was conducted at the same time using meteorological models. It was also confirmed that in the middle latitudes, because the width of that high radiance zone was broadening in summer, the marine traffic surveillance system which used the mid-infrared region provided poor images with very low contrast between islands, ships, and the background so the images even disappeared.

Simultaneous studies of dissolved organic matter and chlorophyll (alpha) fluorescence intensity horizontal distributions were carried out by the method of a remote-acting laser fluorometry in the eastern part of the Black Sea. Investigations of upwelling radiation spectra from the subsurface layer of seawater in a passive mode also were carried out. A computer program for graphic representation of the data statistical processing results was created. Correlation functions of the distributions were studied. Some results of experimental data processing are represented as isolines on electronic maps of sea areas under consideration. The existence of spatial nonuniformities with a different scale in the fluorescence fields was found to take place. Multipurpose applications of the multi-channel analyzer of spectra are discussed.

The problems of sea ecological monitoring are discussed. It's established that identical operative estimations of a situation in coastal regions can be made with the aid of in situ measuring of total (integral) ecological parameters. The examples of such estimations are given. Peculiarities of remote sensing applications in colored and turbid waters are examined.

A model for prediction of visibility in nearshore waters must estimate inherent optical properties directly from spatially and temporally varying concentrations of optically important organic and inorganic materials. Models which describe these concentrations utilize both theoretical and empirical relationships. The estimation of coastal underwater visibility is based on Mie scattering calculations combined with laboratory measurements to obtain a set of calibration constants used to calculate the inherent optical properties from concentrations of generic water column constituents. These constituents are presently limited to sediments, phytoplankton and colored dissolved organic materials. Number concentrations of cells and sediment particles, normally provided by water constituent source models, were measured in the laboratory. These measurements were taken over a range of sediment and phytoplankton concentrations. Modeled scattering and absorption estimates are compared with laboratory data and data from one coastal station. The optical modeling procedures provide acceptable estimates over the range of available data, but begin to deviate as the proportion of large particles increases in very turbid waters.

In this study the main features of the light scattering by an air bubble in water are summarized using Mie scattering calculations. The possible contribution of persistent populations of microbubbles to total scattering and backscattering coefficients of sea water in quiescent seas is evaluated. This assessment is made assuming various concentrations and size distributions of bubbles larger than 20 micrometers in diameter, which are representative of surface waters during nearly calm sea conditions. It appears that the contribution of these bubbles to the total scattering and backscattering coefficients cannot be neglected in some oceanic situations. This contribution varies between a fraction of 1% to several percent, and might possibly be as high as a dozen or so percent. The major uncertainty in these calculations is the lack of simultaneous measurements of bubbles and light scattering. In addition, because no in situ data about bubbles less than 20 micrometers in size are available, these small bubbles are not taken into account in the present assessment.

A preliminary investigation is made of a method to estimate the spatial distribution of an optical source at a single wavelength in a spatially uniform seawater of known absorption and scattering properties. The source at the wavelength of interest could be inelastic scattering, fluorescence, or bioluminescence, for example. An algorithm is developed with which to estimate two coefficients that describe the source from only downward and upward irradiance measurements at two depths that can be far apart, or four coefficients if the downward and upward scalar irradiances also are measured. For the special case of a spatially uniform, semi- infinite seawater then measurements at one depth are sufficient but the number of coefficients that can be estimated is reduced by a factor of two. The algorithm is derived assuming that the radiance is in the asymptotic regime, which means results are less accurate if measurements are made too near the sea surface.

In this paper a method is proposed on how to extract cylinders from single 2D images. The operator restricts the search area for the image ellipse from the projected cylinder, and a least- square ellipse is obtained and verified by the operator. By knowing the radius and length of the cylinder, an algorithm using projective geometry back projects the image ellipse to a circle in three-space. The center and normal vector to this circle are obtained. If both cylinder tangents are visible, a better estimate of cylinder axis is obtained. From this a synthetic cylinder is computed and projected onto the original image. If the synthetic cylinder is a good fit, it is transferred to a CAD model of the environment, which is updated. The operator receives an updated version of the environment, which either includes a new cylinder or a better pose estimate of one of the previously identified cylinders.

This paper investigates the variation in the polarization properties of light scattered by aerosols in the MBL arising from various aerosol sources and environmental conditions. Mie scattering models of Gaussian and log normal distributions of spheres and combinations thereof were used to calculate the polarization properties of light scattered from various models and from experimentally determined distributions of aerosols in the marine boundary layer. The results of the models were verified by comparison to scattering from (NH₄)₂SO₄ particles, a component of aerosols in the MBL that is nearly spherical and readily generated in the laboratory. Calculations indicate that scattering by aerosols is distinctly not Rayleigh-like. The polarization properties of light scattered in the MBL vary with size, refractive index, and number distributions of particles in the MBL. These differences should be instrumentally detectable and could be important for visibility.

Contrast in the reflectivity between pure and contaminated sea surfaces is the result of two effects, namely (1) differing reflectivities of pure sea water and oil on water and (2) damping effect of the oil film on the sea waves. The problem is to estimate their separate contributions to total contrast so that the substance effect can be isolated. Its magnitude provides assessment of the oil film thickness which can be obtained for sufficiently large averaging scales. The spectral behavior and film thickness dependence of contrast have been calculated for an undisturbed sea surface. The estimate of the damping effect has been made using the Cox- Munk distributions for pure and contaminated surfaces. The method chosen has been verified during a series of tests conducted in situ from an aircraft carrying a CO₂ laser sensor operating at 10.6 micrometers .

Contrast of oil film against the rough sea surface background was estimated for the wavelength range from 300 - 800 nm in various observation conditions. Morel and Prieur's experimental data on water reflectance in the visible spectrum were used as the basis for computations. Extrapolations of these data to the UV and IR regions are based on the well-known low- parametric models for water properties. The computations show that the contrast magnitude varies depending on the water type, wavelength, wind velocity and solar altitude from -90% to +60% (plus relates to the case when oil is brighter than water, minus relates to the opposite case). To avoid small or zero contrasts, observations apparently should be fulfilled in several spectral channels. Calculation method was verified during a flight over the Black Sea when predicted oil-water contrast was obtained with two airborne TV-cameras operating in the visible and UV spectral regions.

Particle volume spectra are often inferred from optically measured particle areal size distributions after the areal size distributions have been transformed into equivalent spherical diameter (ESD) distributions. Resolution and sensitivity differences between imaging systems result in different shapes for the measured particle size distribution. Additionally, the sensitivity threshold of the imaging system is not only fundamental to the determination of the particle edge but also determines the optical density level below which material will not be imaged. All this affects the measured size of a particle. This contribution utilizes laboratory data and unique, synchronous, ocean field data collected by three coincident imaging systems to evaluate these effects in the study of large marine particles. An algorithm rooted in the theory of moment invariants is presented which avoids the distortions to the particle size distributions when the size of non-spherical and/or porous particles are presented as ESD.

Two kinds of potentials to solve the scattering from a radially inhomogeneous cylinder are presented. The models of the refraction indices for which these potentials are effective have been considered. The methods developed allow the solution of the scattering problem for any angle of incidence of the plane wave to be evaluated.

In the context of notions earlier developed for absorption spectra the correlation between the suspended matter fluorescence intensity and the solution one is obtained. A model with the help of which the relation has been obtained involves a new method of consideration of exciting radiation absorption and reabsorption of the fluorescence emission by a suspended matter particle. The form of the suspended matter particle was approximated by a sphere. The quantity estimation of this effect value by the example of phytoplankton in the water is considered. The experimental result of the sea water fluorescence intensity changing caused by organic matter transition from phytoplankton cells into the solution is discussed.

This report deals with the problem of estimation of the damages to the environment caused by the crude oil (or oil products) spills from underwater sources. The peculiarities of the oil movement caused by flotation and turbulence in the deep sea were considered on the basis of assumption that the oil dispersed on the separate drops. It is shown that the oil which is coming to the surface is divided into separate clusters in accordance with the sizes of the drops. Mathematical expressions were obtained that permitted us to evaluate the sizes of oil drops and clusters as well as oil concentration depending on time. The analysis of experimental data confirmed the theoretical results while using the diesel oil. Its drops had sizes from 0.10 to 1.34 mm. The diesel oil concentration in clusters corresponds to theoretical predictions.

A model of formation of the sea water fluorescence intensity of dissolved organic matter vertical stratification I(z) is proposed. It allows us to explain the increasing I with z depth on the horizons situated below photic zone. The influence of different hydrophysical characteristics on the I(z) dependence and comparison with experimental data are considered.

The problem of multispectral remote measurements of ocean hydrophysical characteristics by means of optical methods is discussed. The algorithm and method of such measurements are proposed.

In situ measurements of optical properties made from a ship can be biased by the ship's shadow. In an effort to evaluate the ship shadow perturbation created by the R/V Weatherbird II, profiles of downwelling irradiance, E_d(z,(lambda) ), upwelling radiance, L_u(z,(lambda) ), as well as derived apparent optical properties (AOPs) were obtained at distances of 1, 3, 6 and >= 20 m off the ship's stern. Two statistical analyses are explored here. The first compares the mean difference between simultaneously obtained fluxes and AOPs sampled at distances greater than 20 m from the ship to those taken 1 and 6 m off the stern. The second analysis compares derived AOPs taken at each of the four distances throughout the length of the experiment. Only rarely are significant differences found for data beyond three meters off the ship's stern; however at 1 m off the stern significant discrepancies are intermittently observed. This work illustrates that the inherent sources of noise in determining fluxes and AOPs in the upper ocean are generally greater than the effects incurred by the ship's own shadow under optimal conditions.

An inverse problem of ocean optics is solved for estimating the scalar irradiance and a source, such as fluorescence, bioluminescence, or Raman scattering, or an optical property such as the absorption coefficient. The solution requires in situ measurements of the downward and upward irradiances and a priori estimation of the angular shape of the volume scattering function. The iterative inversion procedure is developed from asymptotic two-stream radiative transfer equations and the conjugate gradient method. Preliminary numerical tests show that the algorithm is quite accurate in the region away from the surface but gives appreciable errors close to the surface where the asymptotic two-stream equations are a poor approximation.

In order to increase the accuracy of measuring the chlorophyll concentration from shipboard or satellite and to find out maximum potentials of remote sensing, the method of mathematical design of experiment is recommended. It is shown that the optimum design includes not more than two wide composite spectral channels. A recurrent algorithm for selection of the optimal spectral channel is suggested. In order to use this algorithm, one must know statistical characteristics of the system `water-leaving radiance spectrum-chlorophyll concentration in surface waters.' They were simulated on the basis of well-known low-parametric models for water optical properties because of the lack of experimental data on these characteristics. Optimal spectral channels have been computed and an example of chlorophyll concentration retrieval is shown. They may be considered as preliminary results demonstrating possibilities of the experimental design method.

Two models of relative spectral reflectances as a function of chlorophyll-like pigment concentrations in the upper layer of oceanic waters and thus absorption and scattering properties of phytoplankton are described. These models are developed on the basis of statistical relationships between measured spectral diffuse attenuation coefficients and chlorophyll density in various oceanic waters (from oligotrophic to eutrophic). The semi-empirical model includes new spectral irradiance measurements in different waters. The strongly nonlinear regression equation (reflectance v. chlorophyll concentration) is compared with direct measurements, giving a negligible systematic error and a standard deviation of only 15% and of 20%, if applied to other spectra. The theoretical model is based on the principle of invariance of the emergent radiation for a semi-infinite plane-parallel medium, the delta function approximation for the forward scattering peak, the approximate solution of the radiative transfer equation as well as Cox and Munk's statistics of the roughness of the sea surface. It recovers formulas derived by others with more complicated models. Both models convert reflectance or reflected radiances reliably into inherent optical phytoplankton properties for different open ocean waters, indicating no need for a regional algorithm.

Development of water quality retrieval algorithms is discussed in terms of causal dependence of the upwelling spectral radiance upon the water composition. Unlike clean marine/oceanic waters for which linear regression retrieval relationships are valid, inland and coastal zone water masses with high degree of optical complexity necessitate the development of nonparametric retrieval approaches. At the basis of these techniques are models considering the optical competitiveness of several coexisting aquatic components. Such models for Lakes Ladoga and Ontario are described and compared. Monte Carlo simulations have been performed to analyze the spectral and angular variations of the upwelling radiance scattered by the water column out into the atmosphere. Analysis of optical conditions for running remote sounding natural waters of various optical complexity is carried out. Relevant recommendations are formulated.

In this study, the bidirectional character of the ocean reflectance has been taken into account in the processing of coastal zone color scanner (CZCS) imagery, taken as an example. This effect is represented by a factor Q, which relates a given upwelling radiance to the upwelling irradiance. In this study, the Q factor has been calculated for many cases, using Monte Carlo simulations and a lookup table for Q has been produced for the wavelengths corresponding to the CZCS channels. The Q((lambda) ) values computed for a chlorophyll concentration of 0.3 mg/m³, are used for a first iteration in the pixel-by-pixel processing method developed for CZCS data. The chlorophyll concentration obtained at the issue of this first loop is used to adjust the Q factor and the chlorophyll concentration is again computed. These iterative calculations are repeated until the convergence in the chlorophyll values is reached. The final results generally show higher values in chlorophyll than those obtained with Q equals 4.5, by 20 - 80%. These tests show that convergence is rapidly obtained and that two iterations suffice to obtain stable values of chlorophyll concentration.

The impending launch of a number of remote sensing platforms such as the NASA SeaWiFS (sea-viewing wide field-of-view sensor) has generated renewed interest in instrumentation for measuring ocean color in situ. The increased number of spectral bands desired and the large dynamic range of the measurements place special challenges on the design of these instruments. Of particular interest in measurements of spectral irradiance and in the calculation of irradiance reflectance are errors introduced by the departure of the instrument response from a true cosine at increasing angles of incident irradiance. Using field data as well as a modelled radiance distribution, this paper presents an evaluation of a commercial cosine collector for measurements of spectral irradiance. Preliminary results form a new program sampling the variability in immersion coefficient are also presented.

In turbid waters of coastal zones (case II water) the retrieval of the concentration of chlorophyll from remotely sensed spectral radiances becomes difficult because of the influence of gelbstoff and suspended matter on the radiance spectrum. For the coastal zone color scanner (CZCS) an inverse modeling method was developed to derive the concentrations of gelbstoff, suspended matter and chlorophyll, and the aerosol path radiance. The minimum error we have to expect for this system is analyzed by modeling the concentration change which is necessary to cause a change in the radiance corresponding to 1 digital count. The determination of the minimum error in the retrieval procedure is based on the evaluation of the Hesse Matrix of the chi square function. It turns out that for case II water the channel most sensitive to changes to all three groups of water constituents is CZCS 4 at 670 nm. The retrieval of the concentration is most difficult for chlorophyll, while the error for suspended matter and gelbstoff and for the aerosol path radiance is much smaller.

The variation of optical properties of water was studied in the open Baltic Sea and in coastal waters of the Pomeranian Bight for more than ten years. The optical properties in the open Baltic Sea are strongly influenced by plankton blooms with typical phytoplankton compositions. This led to significant seasonal variations in spectral reflectances. In coastal waters of the Pomeranian Bight, the origin of the water masses and the dwell period of the river water in different lagoon-like areas and bays determine the composition of the water constituents and their optical properties. Strong temporal and spatial variations in spectral reflectance, the spectral absorption of phytoplankton pigments, detritus and yellow substances were found within an area of 50 km². The data set was used to develop ground truth algorithms to determine water constituents of Baltic Sea water from satellite data using CZCS, SeaWiFS, and MERIS.

We have developed a bistatic, polarization-modulated nephelometer for making in situ measurements of angle- and polarization-dependent light scattering in sea ice. The instrument sits directly and noninvasively on the surface of the sea ice, and can also be used for studying scattering in seawater. A visible laser beam is directed into the medium and the scattered light is detected by the analyzer optics. Both laser and detector angles can be varied. The technique of ac polarimetry is used to accurately obtain phase function and polarization information of the scattered light. This instrument was tested by scattering from monodisperse polystyrene (latex) spheres in the laboratory. Results of Mie calculations are in good qualitative agreement with scattering measured in the laboratory. This instrument was used to measure the angle- and polarization-dependent scattering in sea ice at Pt. Barrow, Alaska May 1994. Preliminary findings indicate a large polarization signal associated with the orientational ordering of the sea ice crystallites.

Fluorescence spectroscopy has been used to characterize and assess the vertical distribution of dissolved (DOM) and particulate matter (POM) entrapped in sea ice. Fluorescence excitation- emission of bulk particulates, performed on first-year ice and multi-year flow ice, indicated that microalgae present in different layers of the first year ice resembled typical water column phytoplankton spectra, where those in the multi-year ice samples resembled detrital spectra. Fluorescence analysis also indicated that DOM present in sea ice can be characterized by their excitation-emission in unconcentrated samples. Maximal values for DOM fluorescence were observed at shorter excitation wavelengths (250 nm - 300 nm), with an emission centered between 390 - 425 nm.

The distribution and concentration of particulate and dissolved material were determined for first year and multiyear sea ice collected from the fast ice off Barrow, Alaska. The particles were identified as intact algal cells, bacteria, organic aggregates colonized by bacteria and detrital particles. The largest concentrations of particles occurred in the zones of fine grain or in zones of concentrated brine drainage features. The absorption efficiencies of these particles in combination with measured particle concentrations were shown to provide a reasonable estimate of the bulk particulate spectral absorption coefficients in the case of a first year ice sample. The sum of the absorption coefficients of the particulate and dissolved fractions were up to an order of magnitude greater than the absorption coefficients of pure ice. The enhanced absorption of visible radiation by the entrapped material was estimated to cause increases in sea ice temperature of up to 3 degree(s)C per day in the absence of snow cover. The marine- derived particulate and dissolved materials are not negligible contributors to the optical and thermal characteristics of sea ice.

An apparatus has been developed to measure the optical scattering of laser light from the water-ice interface of sea ice. To avoid changes that occur in the optical characteristics of inhomogeneous natural sea ice when removed from its environment, this apparatus operates in situ. Testing with this apparatus was conducted on shore-fast ice at Resolute Bay in Canada. We investigated the capabilities of this apparatus to measure in situ scattering profiles from the underside of the ice (the water-ice interface) as a function of detector angle. Testing was conducted on ice containing biological material in the bottom layer and on ice cleared of 0.5 cm of this bottom layer. Results were compared to characterize the optical effects of the biological material layer.

A recently developed radiative transfer model is applied to study the transport of photosynthetically active radiation (PAR) in the whole coupled atmosphere, sea ice and ocean system. This model rigorously accounts for the multiple scattering and absorption by the atmospheric molecules, clouds, snow and sea water, as well as the brine pockets and air bubbles trapped in sea ice. Both the spectral distribution and the seasonal variation of PAR at various levels in the ice and ocean have been investigated for different conditions. Results show that clouds, snow and ice algae all have important effects on the PAR availability to the microbial community under ice. The algae in the ice also significantly alters the spectral distribution of PAR transmitted to the ocean. Compared with the effects of clouds, snow and ice algae, the effect of changes in the amount of ozone in the atmosphere, the main absorptive gas in the PAR spectrum, on the amount of PAR entering the ice and ocean is negligible.

Beam spread measurements have been made on sea ice samples and used to develop estimates of the volume scattering function at small scattering angles. In this technique Gaussian-like modelled beam spread functions (BSF) are used to derive the modulation transfer function (MTF) and Well's theory is applied to estimate the volume scattering function for the sea ice medium. A Monte Carlo model for beam propagation through homogeneous sea ice layers was used to estimate beam spreading and the surface distributions of irradiance and radiance. Light scattering was assumed to occur from the presence of spherical bubbles trapped within the ice. Volume scattering functions used in the model were calculated with Mie theory or derived from measured BSFs. The BSFs generated by the model, using estimated optical properties, were found to be comparable to those derived from the transforms over a range of ice thicknesses. The scattering transform technique was applied to beam spread data collected during Arctic and laboratory experiments for samples of young, first year, and multiyear ice to derive estimated MTF values. Requirements and limitations for applying this technique to sea ice are discussed.

Optical tweezers is a term used to describe the optical force generation and confinement process by a highly focused laser beam. The forces exerted by the tweezer are sufficient to confine and move cells and particles without physical contact. When integrated with fluorescence or scattering detection, the laser tweezer can become a powerful instrument for the rapid characterization of the optical properties of isolated organic marine particulates and phytoplanktonic cells, from which bulk properties may be inferred. This technique offers the advantage of studying planktonic cells and organisms in their natural environment by confinement without immobilization, thereby preserving the spectral absorption and fluorescence properties of the samples under study. Herein, we report, for the first time, on the measurement of the spectral fluorescence and scattering of cyanobacteria and diatoms which have been confined by an optical tweezer. Preliminary data shows the characteristic emission peak from the chlorophyll (alpha) pigment (685 nm) for both samples, as well as spectral features that may be related to other photosynthetic pigments.

Results are presented of a series of investigations carried out at the Department of Hydrooptics of SOI with the aim of development, design, and practical employment of optical instruments for measuring the statistical characteristics of turbulent inhomogeneities in seawater. The developed modifications of phase-contrast methods (shadow methods) make it possible to detect the variations of light beam angle-of-arrival at the level of 0.03' - 0.05'. The interpretation of registered signals from photo-electrical output of the optical instrument is based on the connection between the signal correlation function or spectrum and the energetic spectrum of refractive index fluctuations. The corresponded relations are obtained with the help of the theory of light propagation in random media. A measurement of optical fluctuations spectrum in turbulent flow behind a heated grating in hydrodynamic tube is shown to demonstrate the designed instrument's abilities. Some results of in-situ experiments made in calm waters and in turbulized layer near thermocline are presented.

A prototype instrument has been developed to measure the settling velocity of marine particulates using optical techniques in an in-situ settling chamber. Particles from 100 micrometers to several mm are imaged by a shadowgraph system, which has a 30 cm depth of field. Particles in the 10 to 100 micrometers range are monitored by a laser diffraction system. Flow management considerations have been incorporated into the instrument to ensure minimal disruption of the aggregates and their settling rates. We present the results of laboratory tests in which the settling rates of polystyrene spheres and natural marine particulates have been measured using the component systems. Design considerations for the self-contained moored version are also specified.