This PDF file contains the front matter associated with SPIE Proceedings Volume 11529, including the Title Page, Copyright information, and Table of Contents.

Across the world, many coastal tidal regions are unsafe to navigate due to shifting mud and sand pushed by water currents. Ability to regularly map the current location of a channel will aid safe passage for commercial, leisure and rescue craft. This work investigates the use of synthetic aperture radar data derived from satellites to provide accurate mapping of moving channels in coastal regions. As images must be collected at low tide, data availability is assessed considering the relationship between the orbital motion of the satellites and the tides. Change detection methods are applied to suitable images to map changes in the location of navigable channels. Pixels that undergo similar changes over time (e.g. from water covered to exposed sand) are grouped together by examining the principal component of the covariance matrix, for a vector composed of pixel values from the same location at different times. The Solway Firth in Great Britain is selected as a trial site as it is exposed to some of Europe’s fastest tidal movements and ranges, and hence is one of Great Britain’s most treacherous stretches of coastline.

Satellites are equipped with an array of diversified sensors, capable of relaying multiple types of optical data about the earth’s surface. The different sensors used can capture varying levels of detail for a particular area of interest. Combining information gathered from sensors, ranging from the infrared to the visible spectrum, can enhance visualization and depth of data. The application of principal component analysis (PCA) to data fusion is traditionally processed by weighted reliability matrix. This paper presents a novel weighted reliability with rejection control PCA based sensor algorithm to improve data fusion quality creating a more robust visualization of the composite information obtained from satellites. The proposed algorithm can be applied using both L₂ and L₁ PCA. Simulation studies validate the proposed controlled weighted fusion method, even under high levels of corruption.

Uncertainties in the retrieval of remote sensing reflectance, R_rs, from Ocean Color (OC) satellite sensors have a strong impact on performance of algorithms for the estimation of chlorophyll-a concentrations and inherent optical properties (IOPs). Uncertainties are highest in the blue bands, especially in coastal waters with low blue-band Rrs values. We recently showed that the main uncertainty contributions when observing at sun glint-optimized geometries are due to two components: variability of in-water parameters and skylight reflected from the water surface. Sunlight propagates to the water and back to the top of the atmosphere (TOA), capturing the instantaneous state of in-water conditions and sky light reflected from the wind-roughened wave facets. Both processes are averaged with the spatial resolution of the sensor. This results in the satellite measured TOA radiance spectrum, which is typically different from vector radiative transfer simulations that are based on the mean values of sea surface reflectance coefficient. Preliminary analysis shows that these two uncertainty components are spatially highly variable. Using the recently released provisional Aquatic Reflectance product for Landsat 8, we analyzed spatial scales of these components for multiple scenes in the open ocean and coastal waters at spatial resolutions ranging from 30 m to several kilometers.

Biogenic oil film is a natural surface slick that is mainly derived by sea flora and fauna. The often observation of the film near aquaculture facilities has raised awareness on the possibility of the linkage between the development of the film and the anthropogenic activities taking place on site (i.e. artificial feeding and liquid waste). This study aims to investigate the possibility of the detection of biogenic oil film on optical satellite images and discriminate it from other oceanographic phenomena. For the purposes of the study we have used a Sentinel-2 (S2) dataset consisted of 73 images for the year 2019 to detect the film on three aquaculture areas. An automatic procedure was developed on a Python based algorithm which included the following stages: (a) downloading images, (b) preprocessing the input data, (c) identifying dark formations in the adjacent fish farming area, (d) extracting attribute tables with the statistical characteristics of the formations (shape, area, etc.), (e) classification of formations as biogenic film or other (lookalike) and (f) extraction of biogenic film vectors. The developed algorithm was able to detect biogenic oil film successfully however some misleading results regarding the decision of true or false positive (biogenic oil film or lookalike) was evidenced. The efficiency of the algorithm was tested against manual classification with overall accuracy 82,6%. As further step the results of this study should be validated with in-situ measurements and further work is required to verify the results obtained by testing the methods in other sites.

High-resolution information of the marine environment is very important for the protection and the management of marine species. In recent years, the ability of the unmanned aerial systems (UAS) to acquire remotely, high-resolution imagery has made them very popular in the marine remote sensing field. Observations in the marine environment are very challenging in many ways as they are affected by weather and oceanographic conditions that interact with each other. The UAS aerial surveys deal with many limitations affecting the quality and reliability of the acquired data, directly dependent on the environmental conditions prevailing in the survey area. For example, high wind speed affects the sea surface state and the safety of a UAS survey, resulting in unsatisfying observations of the marine environment. This study presents the validation of a UAS toolbox designed to calculate the optimal flight times on a day for UAS surveys. The ruleset of the toolbox is based on a theoretical UAS data acquisition protocol which summarizes all the parameters that affect the quality and reliability of the UAS acquired data in the marine environment. For the validation of the toolbox, flights were conducted in different conditions, according to the toolbox predictions, while underwater targets were placed and compared as to their characteristics in different conditions. The aerial images of each flight were processed for the creation of high-resolution orthophoto-maps that showed significant differences between the optimal flight times and the non-optimal flights. The present work emphasizes the importance of the environmental conditions during an aerial survey and evidence that data quality is superior during the toolbox suggested flight times.

Sentinel-2 offers the capabilities to observe Arctic sea ice features with high spatial and temporal resolution. Arctic sea ice drift, however, exacerbates observing the temporal evolution of floes by means of time series analysis. We therefore developed a novel rotation-invariant ice floe descriptor based on ice floe geometry and an image-processing workflow consisting of three main steps: (i) ice floe extraction, (ii) ice floe description and (iii) ice floe matching. We tested the methodology on Sentinel-2A images from 10 June and 3 July, 2017, and selected five floes present in both images. We further added ten “false samples” in the second image. All floes from the first image were correctly identified and matched with the floes from the second image. The methodology enables the identification of individual ice floes and determination of their relative rotation from multiple Sentinel-2 images.

Remote sensing of wind waves propagating in the areas covered by ice at initial stages of its formation in the marginal ice zone using radar is an urging problem for mapping ice boundaries and their dynamics. Another aspect of the problem is to investigate possibilities of discrimination between the marginal ice zone and oil spills in radar imagery. This study is focused on modeling the damping of surface waves due to ice floes in laboratory and field experiment. Laboratory experiments were carried out is a container filled with pure water in order to exclude the effect of surfactant films on wave damping. The container was mounted on a vibration table, so that surface gravity-capillary waves (GCW) could be parametrically generated in the container when the amplitude of the vibrations exceeded some threshold level. The wave damping coefficient could be retrieved when measuring the threshold. The floes in experiment were modeled using thin plastic pieces of two different sizes, the relative square of the “floe” coverage of the water surface was controlled in experiment. The dependences of the damping coefficient at different relations between the surface wavelength and the floe dimensions as functions of the floe coverage area were obtained. It is obtained that the damping of gravity-capillary waves in the presence of floes comparable in size with GCW can be one to two orders of magnitude greater that the wave damping due to inextensible film. Preliminary field experiments have been conducted on the Gorky Water Reservoir using a research catamaran vessel of the Institute of Applied Physics. Plywood pieces with sizes several times smaller that the studied surface wavelengths were used as imitators of ice floes and were deployed in between the catamaran hulls. Surface waves propagating between the halls were generated mechanically by a vertically oscillating motor boat. The amplitude of attenuating surface waves due to the “plywood floes” was measured with wire gauges mounted at the bow and the stern of the catamaran. The damping distance due to ice floes obtained in the field experiment was estimated as about 10 wavelengths thus indicating that that wave suppression due to the floes was essentially stronger than the viscous wave damping for clean or contaminated water surface. Wave damping observed both in the laboratory and field experiments can be comparable with the wave damping due to crude oil/oil emulsion films, so the problem of discrimination between, e.g. grease ice and oil spills in radar imagery can be nontrivial.

The new mathematical models of the statistical moments of the Snell's window image are proposed. These models are based on the use of a binary representation of the Snell’s window image and a Gaussian slope distribution function. It leads to express statistical image moments in terms of the error function. Using its well-known properties, it was possible to establish analytical relationships between the AI differentiated by the zenith angle with the slope variance, as well as between the twice-differentiated ACF of the image with the ACF of the surface slopes. The obtained expressions can already be used in practice to solve inverse problems by a numerical method. At the same time, the results of numerical simulation show that the Snell’s window image is an object very sensitive to changes of the roughness of the sea surface. With an increase of wind speed or in the presence of a surfactant film, the number and sizes of patterns near the Snell’s window border significantly change that manifests in the statistical moments of the image. This result indicate that the presented method can be used to study the variability of the spectra of wind waves in the field of near-surface hydrophysical processes, as well as in the presence of surface pollutants.

As marine traffic has increased, the importance of ship detection using remote sensing images has been emphasized. Especially, with a better performance for discrimination of target, the usage of hyperspectral data for marine surveillance has been increasing recently. In this study, we detected the vessels on airborne hyperspectral images and quantitatively analyzed the detection results. To obtain the airborne hyperspectral images and auxiliary data for the quantitative validation, the in-field airborne imaging experiment was carried out. In addition, four different end-member extraction techniques including N-FINDR, PPI, ICA, and VCA were applied for comparison of detection performance with hyperspectral unmixing methods. Detection results present significant differences by endmember extraction techniques. The N-FINDR and VCA techniques presented a total of 14 vessels, while the ICA technique detected seven vessels, and the PPI technique detected two vessels. The pixel-based probability of detection and false alarm ratiofor all 14 ships were 98.83% and 4.30%, respectively. This study also addressed the important role of abundance fraction analysis for marine surveillance purpose.

For decades, the global remotely sensed significant wave heights have been from altimeters and/or synthetic aperture radars in wave mode, which both suffer from spatial and temporal sampling limitations. In contrast, spaceborne scatterometers are with large swath and high temporal revisit frequency at a global scale, but so far are routinely providing ocean winds rather than waves. This paper addresses the ocean sea state retrieval algorithm by applying state-of-the-art machine learning technology to European Advanced Scatterometer (ASCAT). A huge collocation database (< 6 million) has been built between L1b/L2 ASCAT products and WaveWatch III (ww3) ocean wave hindcasts within the spatio-temporal criteria of 0.1 degree and 0.5 h for the period of three years, followed by the mining of this big data by means of machine learning (i.e., multi-hidden layer neural network here). The neural network proposed here includes layers: the input layer (13 ASCAT variables), four hidden layers, and the output layer (wave heights). The performance of machine learning based approach for ocean wave height estimation from scatterometer is evaluated using two independent match-ups: ASCAT-WW3 and ASCAT-buoy. The statistical assessment against SWH hindcast shows the root mean square error of 0.55 m and scatter index of 23%, respectively. Results indicate that the data driven algorithm is reasonable for sea state estimation from wide-swath scatterometers, and encouraging for operational implementation in the future.

This paper summarizes two approaches for estimating remote sensing reflectance by above-water method. One, represented by M99 and R06, is used to estimating the sea-surface reflectance ρ, while the other, represented by G01 and L10, is applied in estimating and eliminating the contribution of residual surface-reflected light and sun glint ε. Base on the second approach, this paper proposes a new approach (HY approach), which use the quasi-analytical algorithm to estimate the remote sensing reflectance of near infrared band, and then estimate and eliminate ε. Given the preliminary estimates of 𝑅_𝑟𝑠(λ), we can use quasi-analytical algorithm to estimate the inherent optical properties (IOP) of the visible spectrum. With IOP model, IOP of the near infrared band can be calculated, which then can be used to estimate the 𝑅_𝑟𝑠(NIR) of near infrared wave band. And ultimately the estimating of the ε can be realized. The in-situ data were gathered in September, 2018 in the East China Sea and the South China Sea, from 76 stations. The remote sensing reflectance (Rrs) was calculated simultaneously by above-water and in-water methods. Comparing the data analyzing result of HY approach in this paper with other approaches, the variation coefficient of HY and L10 is within 5% for most stations, and within 10% for HY and R06. Compared with the results of Rrs measured by in-water method, the variation coefficient of 80% of the stations is within 15%, and the results of the two methods have a good consistency. HY method avoids the problem of extra measurement of sea surface wind in methods such as R06. This method has simple and clear steps, fast iterative convergence and better calculation speed than L10 method.

Traditionally spiral slick structure is interpreted as a manifestation of marine eddy, which length scale is taken equal to the scale of spiral. This approach is based on the assumption that wind has no effect on the kinematics of forming slick bands which, according to our estimation, is incorrect in real sea conditions. This can lead to misinterpretation of remote sensing data in the field of definition of the characteristics of marine eddies, particularly, in radar images. The system of equations for the description of kinematics of a Lagrangian particle (element of surface active substance) in stationary fields of axisymmetric eddy with non-zero radial velocity component and homogeneous wind was obtained. It was shown that the center of the spiral is not collocated with the center of the eddy, and the distance between them can achieve the scale of eddy core. It was shown that the displacement of the spiral center is quasi perpendicular to the wind direction in case of small radial velocity component compared to the tangential one. It was shown analytically that there is a threshold wind velocity which corresponds to the breakdown of the spiral structure. Simulation based on the discrete-time approximation of particle trajectories, as well as radar observation of marine eddies, demonstrates the possibility of appearance of a “focus” and a “saddle” in the characteristic shape of slick bands. The perspectives of correct retrieval of length scales and character velocities of observed sub mesoscale marine eddies are discussed.

Island mass effect, which is accompanied by higher bio-productivity and closely associated with fishing activities, was observed in many island (reefs) areas. Recently, we found the Chl-a enrichment (the annual mean≥0.14 mg/m³) in the surrounding of the reefs and atolls in the Xisha Archipelago, based on the daily MODISA Level-2 data during the years of 2003 to 2017. The DINEOF algorithm was used to filling missing values in the MODISA data. The analysis results show that: 1) Generally, the Chl-a concentrations became larger in winter (November to January) and smaller in summer (May to July) in the XA; The seasonal variation of Chl-a is strongly related to the Mixed Layer Depth, which is larger in winter and smaller in summer. 2) In the XA, higher Chl-a were observed in the lagoons of the atolls, where is shallow and nutritious. Hovmoller diagrams of daily MODIS Chl-a along the transect of several atolls show that higher Chl-a also appeared in the downstream side. It seems that the lagoons are the sources of the Chl-a, and the turbulent currents transfer and maintain the higher Chl-a in the downstream wakes.

In this paper, we attempt to fill some gaps in the knowledge of the oil pollution pattern in the whole area of the Caspian Sea on the base of the remotely sensed data. We present the results of a long-term survey of the Caspian Sea by use of satellite SARs and multispectral sensors. Our primary attention is focused on the oil showings on the sea surface due to natural hydrocarbon emissions from the seabed. During our satellite survey, we discovered a previously unknown seep of petroleum hydrocarbons from the seabed in the shelf area of the Caspian Sea near the Cheleken Peninsula, which belongs administratively to Turkmenistan. We documented its source point as the persistent location of the origins of 379 oil slicks detected in satellite images taken over the area of interest. We also performed the precise estimation of the actual positions of two offshore seeps on the Iranian shelf near the Cape Sefid Rud on the base of 173 and 198 oil slicks correspondently. For these two regions of interest, we compare the release rates of the crude oil from the seabed to the sea surface. Further, we assess the detection rate of oil showings on the sea surface, depending on a sensor type and the season. We put together detailed maps of the sea surface oil pollution caused by natural hydrocarbons seepages on the seabed and determine areas of the high risks of sea surface oil pollution.

This paper reveals the theoretical possibilities of using the underwater solar path images (USPI) to retrieve the wind wave spectra, including situation when surfactant film is on the sea surface. It contains a theoretical model of USPI, an algorithm for retrieval wave spectra through statistical moments of USPI, and results of testing proposed algorithm using numerical simulation. The last one was based on the Elfouhaily wind wave spectrum and the Ermakov model of thin surfactant film. The use of modeling made it possible to establish the main difficulties in achieving a solution of challenging, and also to offer an alternative method. The obtained results confirm the efficiency of the developed method.

We present results of observations of vortex structures in the Caspian Sea based on satellite images of the visible range obtained by Sentinel-2 (MSI), Landsat-5 (ТМ), Landsat-7 (ETM+) and Landsat – 8 (OLI). The initial goal of this work was to identify vortex structures and their main localization areas in the Caspian Sea. In this paper we used Ocean Color Data for two periods: 1999-2006 and 2007-2013, plus 2 recent years (2019 and 2020). Results of these periods were comparing between each other. About 50% of the scenes from the obtained data are covered by clouds due to difficult weather conditions over the Caspian Sea - a frequent changes of air masses in all seasons of the year. Among cloudless scenes, on average, vortex structures occur on 20-30% of scenes. According to the results of the analysis of the data obtained, a predominance of submesoscale cyclones and anticyclones is noted. It was noted that vortex structures were mainly found in the shelf zone of the Caspian Sea. More intense vortex formation is observed in the South Caspian. The main reasons for their formation: the flow of river runoff, complex bottom and coastal topography, the vorticity of the wind field, shear instability at the periphery of the main circulation elements. The mapping of the main circulation elements in Caspian Sea was carried out. For each part of the Caspian Sea, the six main areas of vortex formation were identified.

Recent studies of microwave radar return at moderate and large incidence angles have shown the backscattering is determined by resonance (Bragg) surface waves of cm-scale wavelength range, and by non polarized (non Bragg) component which is associated with wave breaking and quasi specular reflection. This paper is focused on results of field studies of non-Bragg backscattering from the clean water surface and from the water surface covered with surfactant films. The study was carried out using dual polarized X-band radars in the coastal zone of the Black Sea in 2017-2019 at an incidence angle of about 60 degrees. It was found that the radar return contains a Non Bragg component not related to the breaking crests and specular tilt areas at wind speeds from a threshold of the wind wave generation up to wind velocities of the order of 10 m/s. The part of the non-Bragg component not related to the wave breaking crests decreases strongly in the areas of film slicks. At high wind velocities the non-Bragg component out of the spikes is strongly modulated (several times larger than the Bragg component) in the long-wave field, in film slicks the modulation of the non-Bragg component increases. Analysis of the Doppler shifts showed that the velocities of the non-Bragg scatterers correspond to the dm-scale free surface waves and vary slightly in the areas of film slicks. Thus, we concluded that nonlinear features associated with the dm-scale wind waves cause the non-Bragg scattering.

The system of optical devices for remote sensing of near surface layer of the ocean is created. The system consists of a set of original optical devices for recording of range – time – intensity (RTI) images of sea surface from optical sections of the sea surface and camera for the recording of the wave breakings and the sea wave spectra [1-5] by spectral analysis of the sea surface images. These RTI images enable one to receive complete information about kinematics characteristic of various manifestations on the sea surface, including sea surface waves, near surface wind flow manifestations on the sea surface, internal waves (IW) manifestations, oil slicks and so on owing to its ability to screen objects according to their velocity. The recording of wave spectra and temporal variability of the whitecap coverage performs from the photograph of sea surface synchronous with the RTI images of sea surface. A method for retrieval of sea wave’s slopes from RTI images is presented. The system of optical devices is suitable for remote sensing of sea surface from sea platform, ship or vehicle. The brightness angular structure of the cloudless sky is studied based on the model of the sunlight single scattering. These model data are compared to the experimental angular characteristics of the sky brightness obtained due to digital imaging of the horizon from the oceanographic platform. A method for determining the optical thickness of the atmosphere in three spectral ranges of light in real time from the angular height of the horizontal maximum brightness of a cloudless sky recorded with a digital camera was developed. The obtained values of optical thickness can be used in the models of angular distribution of the cloudless sky brightness to provide possibility of retrieval the waves’ statistical characteristics by the remote optical method.

The role of wave breaking in microwave backscattering from the sea surface is a problem of great importance for development of theories and methods of the ocean remote sensing. Recently it has been shown that the microwave radar return is determined by both Bragg and non Bragg scattering components, and some evidences have been given that the latter is associated with wave breaking. However, our understanding of different mechanisms of the role of wave breaking on small-scale wind waves (ripples) and thus on the radar return is still insufficient. This paper presents results of laboratory experiments on the influence of wave breaking on Ka-band radar signals. An effect of the radar return suppression after wave breaking has been revealed and attributed with wind ripples suppression by breaking waves. The experiments were carried out in an oval wind wave tank where intense m/dm-scale surface wave trains were generated by a mechanical wave maker, in particular using a method of dispersive wave focusing. Wind waves were independently generated in the wave tank. A Ka-band radar was mounted at a height of about 1 m above the water level the incidence angle of microwave radiation was about 50 degrees. The experiments were performed both for a clean water surface and in the presence of an oleic acid monomolecular film. It has been obtained that the radar return before the wave train was determined by wind ripples, the radar Doppler spectrum was centered close to the Bragg wave frequencies. The radar signal intensity was strongly enhanced in a wide frequency range when the train was passing by the study area. After the intense wave train the radar return dropped and then slowly recovered to the initial level. We believe that the attenuation of radar backscattering after the wave train is due to suppression of wind ripples by turbulence and surfactants associated with wave breaking.

Analysis of possibilities of identification and characterization of marine processes using their signatures in radar and optical imagery of the sea surface is a very important problem of the ocean remote sensing which has not been solved yet completely by now. Marine slicks which are the areas of suppressed wind waves can be recorded by different sensors and can be indicators of internal waves, non uniform currents, atmospheric convective cells, etc. Field studies including those simultaneous and co-located with remote observations is the most perspective way to the problem solution. An expedition of the Institute of Applied Physics RAS was organized to study the nature of slick bands and its dynamics in the field of various subsurface processes. Field experiments were carried out in the coastal zone of the Black sea from the Oceanographic Platform of Marine Hydrophysical Institute RAS and from the shore. The structure of the currents in the studied area is characterized by significant heterogeneity, so we were able to register different slick structures in the flow field and wind and the slick dynamics. In some experiments, marine slicks were recorded simultaneously in satellite Sentinel images. Observations of surface manifestations of internal waves were carried out using a digital radar station MRS-1000 and multi-frequency radar complex of IAP RAS. At the same time the measurements of currents in the water column were carried out using the ADCP WH Monitor 1200 kHz, wind speed and direction at a height of 30 meters using WindSonic acoustic anemometer. During the passage of internal waves a system of slick bands with a reduced intensity of small-scale waves were observed. Slick bands were observed mainly over the rear slopes of the internal waves; the data from the accompanying measurements showed that the phase velocity was close to the surface current velocity. Theoretical analysis has shown that in this case the convergent zones, where surfactants are accumulated were formed at the rear slopes of the internal waves. This mechanism of slick formation was predicted earlier theoretically and then was modeled in laboratory experiment.

The paper considers the results of a promising method for remote determination of parameters of dynamic processes in the ocean – coherent ocean radar sensing. This work proposes a methodology for determining the speed and direction of the sea surface current and wind waves spectrum by measurements of X-band Doppler radar. Based on the Doppler Effect, it is possible to measure the orbital velocities of wind waves on the sea surface, the velocities of breaking waves, the velocities of the sea surface current and the speed parameters of other oceanic dynamic processes. Using the basic expressions of the wave theory of free waves on water, it is possible to restore the heights of wind waves without additional calibration. Theoretical numerical simulation of the Doppler velocity of the Bragg waves in the field of wind waves and currents were carried out. The simulation used a two-scale model of microwave scattering on an wavy water surface, taking into account the shading of the sea surface by wave crests. A correlation analysis of the surface current, calculated through hydro meteorological parameters and Doppler radar panoramas, showed a maximum correlation coefficient for a velocity value is about 0.88 with a root mean square error of 8 cm/s, and for a direction is about 0.98 with a root mean square error of 14 degrees. The work shows the possibility to recover wind wave spectra from the data on the Doppler shift of microwave radio waves. Features that are not described by the two-scale model are found and discuss.