The Hyper-Angular Rainbow Polarimeter-2 (HARP2) was launched on board the Plankton, Aerosol, Cloud and ocean Ecosystem (PACE) mission, in February 2024, for the global measurement of aerosol and cloud properties as well as to provide atmospheric correction over the footprint of the Ocean Color Instrument (OCI). HARP2 is designed to collect data over a wide field of view in the cross-track direction (+/-47deg) allowing for global coverage in about two days, as well as an even wider field of view in the along-track direction (+/-54deg) providing measurements over a wide range of scattering angles. HARP2 samples 10 angles at 440, 550, and 870nm focusing on aerosol and surface retrievals, and up to 60 angles at 670nm for the hyper-angular retrieval of cloud microphysical properties. The HARP2 instrument collects three nearly identical images with linear polarizers aligned at 0°, 45°, and 90° that can be converted to push-broom images of the I, Q, and U Stokes parameters for each angle, and each wavelength. The HARP2 technology was first demonstrated with the HARP CubeSat satellite which collected a limited dataset for 2 years from 2020 to 2022. HARP2 extends these measurements to a full global coverage in two days, seven days a week.
The development of science quality miniature payloads for nano satellites has facilitated the implementation of private observatories and even constellations of satellites for all sort of applications. GRASP Earth is currently developing a payload system composed of a multi-angle imaging polarimeter for the measurement of aerosol pollution and a high-resolution spectrometer for the measurement of greenhouse gases like CO2 and CH4, with commercial applications. Based on these measurements the GRASP (Generalized Retrieval of Atmosphere and Surface Properties, https://www.grasp-sas.com/) algorithm can simultaneously retrieve detailed details on the aerosol microphysics including particle size, refractive indices, particle sphericity, and the particle absorption properties, as well as the concentration of the greenhouse gases. These measurements performed from a single platform, and the joint aerosol and gases retrieval by GRASP produces higher accuracy and better sensitivity than each measurement perform independently.
PHOTONS is the french component of the AERONET sun-photometer network which provides globally distributed
near-real-time observations of aerosol spectral optical depth and sky radiance as well as derived parameters such as
particle size distributions, single-scattering albedo and complex refractive index. Now more than 12 years of worldwide
distributed data from the network of ground-based radiometers are available. These data are best suited to reliably and
continuously derive the detailed aerosol optical properties in key locations. Mid 2007, about 40 sites mainly located in
France, Europe, Africa as well as in Asia are managed by PHOTONS. Since 2001, the network also contributes to
passive/active sensors synergies. Several sites in France, western as well as eastern Europe, sometimes in connection
with EARLINET, are equipped with both lidar system and sun-photometer dedicated to aerosol and cloud observations.
These synergies will be enhanced in the future mainly within the context of A-Train experience. In this paper, we
provide a general description of PHOTONS network activities and facilities, and present recent results both on
instrumental side (development on new sun-photometer, vicarious calibration methods), on scientific side (A-Train
mission validation like aerosol retrieval algorithms of PARASOL) and aerosols retrieval from ground-based
measurements method.
The AERONET inversion products provide powerful information for understanding column integrated aerosol
properties particularly given the wide global distribution of sites and the 13 year record for some sites. Significant
evolution of the instrument, data quality, ancillary input data and inversion algorithm has necessitated release of
Version 2.0 and establishment of criteria for quality assured products. This paper documents version 1.0 quality
assurance criteria and the analysis of the entire retrieval record available for the Version 2.0 to revise the quality assured
criteria. The result is an improvement in the number and quality of aerosol inversion parameters for most sites through
the entire AERONET data record.
Ambient air pollution with particulate matter constitutes a significant public health danger. The potential health effect
depends on parameters of suspended particles. The paper develops a procedure for studying aerosol microstructure
variability in the lower atmospheric layer over the territory of an industrial center by a multi-wavelength scanning lidar
and a Sun-sky radiometer. An algorithm for data processing of a comprehensive experiment uses integral optical
parameters of the aerosol layer provided by the radiometer as a prior information to process lidar data while retrieving
spatial distribution of aerosol microstructure.
A long series of combined lidar and radiometer measurements have been carried out in Minsk. The observed temporal
changes of total column amount of fine and coarse aerosol fractions are discussed in the paper. Statistical characteristics
of particle size distributions have been evaluated.
The spatial variability of fine and coarse aerosol fraction concentrations was observed over the city. Comparison of
aerosol concentration distributions during two year observations reveals stable zones with increased concentration of
fine particles, possible reason being technological peculiarities of industrial enterprises located in these regions.
Compared to the visible spectral region, very little is known about aerosol absorption in the UV. Without such information it is impossible to quantify the causes of the observed discrepancy between modeled and measured UV irradiances and photolysis rates. We report results of a 17-month aerosol column absorption monitoring experiment conducted in Greenbelt, Maryland, where the imaginary part of effective refractive index k was inferred from the measurements of direct and diffuse atmospheric transmittances by a UV-multifilter rotating shadowband radiometer [UV-MFRSR, U.S. Department of Agriculture (USDA) UV-B Monitoring and Research Network]. Colocated ancillary measurements of aerosol effective particle size distribution and refractive index in the visible wavelengths [by CIMEL sun-sky radiometers, National Aeronautics and Space Administration (NASA) Aerosol Robotic Network (AERONET)], column ozone, surface pressure, and albedo constrain the forward radiative transfer model input, so that a unique solution for k is obtained independently in each UV-MFRSR spectral channel. Inferred values of k are systematically larger in the UV than in the visible wavelengths. The inferred k values enable calculation of the single scattering albedo , which is compared with AERONET inversions in the visible wavelengths. On cloud-free days with high aerosol loadings [ext(440)>0.4], is systematically lower at 368 nm (368=0.94) than at 440 nm (440=0.96), however, the mean differences (0.02) are within expected uncertainties of retrievals (~0.03). The inferred is even lower at shorter UV wavelengths (325~332=0.92), which might suggest the presence of selectively UV absorbing aerosols. We also find that decreases with decrease in aerosol loading. This could be due to real changes in the average aerosol composition between summer and winter months at the Goddard Space Flight Center (GSFC) site.
The knowledge of the global distribution of tropospheric aerosols is important for studying effects of natural aerosols on global climate. Chemical transport models relying on assimilated meteorological fields and accounting for aerosol advection by winds and removal processes can simulate such distribution of atmospheric aerosols. However, the accuracy of global aerosol modeling is yet limited. The uncertainty in location and strength of the aerosol emission sources is a major factor limiting accuracy of global aerosol transport modeling. This paper describes an effort to retrieve global sources of fine mode aerosol from global satellite observations by inverting GOCART aerosol transport model. The method uses an adjoint operation to the aerosol transport model that allows performing inversion with original space (2 x 2.5 degrees) and time (20-60 minutes) resolution of GOCART model. The approach is illustrated by numerical tests and applied to the retrieval global aerosol sources (location and strength) from a combination of MODIS and AERONET observations.
We report final results of an aerosol UV absorption closure experiment where a UV-shadow-band radiometer (UV-MFRSR, USDA UVB Monitoring and Research Network) and 4 rotating sun-sky radiometers (CIMEL, NASA AERONET network) were run side-by-side continuously for 17 months at NASA/GSFC site in Greenbelt, MD. The aerosol extinction optical thickness τext, was measured by the CIMEL direct-sun technique in the visible and at two UV wavelengths 340 and 380 nm. These results were used for UV-MFRSR daily on-site calibration and 3-min measurements of τext at 325nm, 332nm and 368nm. The τext measurements were used as input to the radiative transfer model along with AERONET retrievals of the column-integrated particle size distribution (PSD)to infer an effective imaginary part of the UV aerosol refractive index, k, by fitting MFRSR measured voltage ratios. Using all cases for cloud-free days, we derive diurnal and seasonal dependence of the aerosol absorption optical thickness, τabs with an uncertainty 0.01-0.02. At our site τabs follows pronounced seasonal dependence with maximum values ~0.07 at 368nm (~0.15 at 325nm) occurring in summer hazy conditions and <0.02 in winter-fall seasons, when aerosol loadings are small. Inferred values of k allow calculation of the single scattering albedo, ω, in UVA and comparisons with AERONET almucantar ω440 retrievals at 440nm. Overall, ω was slightly lower in UV than in the visible: case average <ω368>=0.93 compared to <ω440>=0.95. However, the differences (<ω440 - ω368> ~0.02, rms difference ~0.016) are smaller than uncertainties of both retrievals (δω~0.03). Low <ω368> values are consistent with higher values for imaginary refractive index, k: <k368> ~0.01 compare to <k440> ~0.006. However, mean differences in k (<k368-k440>~0.004) were only slightly larger than AERONET retrieval uncertainty δk ~0.00327. We also found that ω decreases with decrease in τext, suggesting different aerosol composition in summer and winter months. So far, our results do not allow explaining the causes of apparent larger aerosol absorption in UV. Continuing co-located measurements at GFSC is important to improve the comparison statistics, but conducting aerosol absorption measurements at different sites with varying conditions is also desirable.
Scientific groups engaged within the frame of the observation networks AERONET and EARLINET perform this work. The methodology of coordinated multi-frequency lidar and radiometric investigation of atmospheric aerosols is being developed for using in network observations. The method to process data of a comprehensive experiment utilizes the approach1,2 designed to process CIMEL data. The retrieval of altitude profiles of aerosol parameters is based on solving a common equation set including lidar equations, equations for the whole atmospheric depth, and constraints on the smoothness of the solutions. The results of numerical experiments are given in the paper to estimate errors while retrieving aerosol parameters. The measurement procedure and algorithms for data processing were refined during the summer-autumn, 2002 at the stations of the Institute of Physics (Minsk, Belarus) and Institute of Geophysics (Belsk, Poland). The stations were equipped by devices CIMEL and three-frequency lidars (532, 694, and 1064 nm). The CIMELs operated according to the routine AERONET program during the measurements. To provide gathering the data on the whole areosol layer, a series of lidar observations was made at different elevation angles. A pro9cedure to successively approach to an optimal estimation of aerosol parameters is proposed in this work to enable data processing with real measurement errors. The results of retrieving vertical profiles of aerosol fraction concentrations are presented for different quality of measurement information.
A Brewer MKIII double spectrophotometer has been modified to measure direct sun and sky radiance from 303nm to 363nm for the purpose of measuring aerosol optical depth, Angstrom parameter, and single scattering albedo. Results from a detailed instrument calibration showed that there is a temperature dependence of -0.3% per degree Celsius, the field of view was 2.6° full width half maximum, and the wavelength calibration was accurately determined using a dye-LASER. Using both integrating sphere and lamp-diffuser plate combinations, absolute diffuse radiometric calibration was performed and converted into direct calibration using the measured field of view. Aerosol optical depth and Angstrom parameter were measured on 4 clear sky days in June 2003 at Greenbelt, Maryland and compared to AERONET-data at the same location. The average difference in the aerosol optical depth at 340nm was smaller than 0.02. A depolarizing element was inserted in the Brewer's optical path to reduce the very pronounced polarization sensitivity, and additional polarized filters were added to explore the possibility to obtain additional aerosol information. Because of a defect in the depolarizer, the current residual polarization is 5%, which has to be reduced to less than 1% to derive additional aerosol parameters from sky radiance measurements.
Compared to the visible spectral region very little is known about aerosol absorption in UV. Without such information it is impossible to quantify a cause to the observed discrepancy between modeled and measured UV irradiances and photolysis rates. We report preliminary results of an aerosol closure experiment where a UV-shadow-band radiometer (UVMFRSR, USDA UVB Monitoring and Research Network) and well-calibrated sun-sky radiometer (CIMEL, NASA AERONET network) were run side-by-side for several months at NASA/GSFC site in Greenbelt, MD. The aerosol optical thickness, τ, was measured at 340nm and 380nm by the CIMEL direct-sun technique. These results compared well with independent MFRSR τ measurements at 368nm (using total minus diffuse irradiance technique). Such comparisons provide an independent check of both instrument’s radiometric and MFRSR’s angular calibration and allow precise tracking of the UV filter degradation by repeating the comparisons made at somewhat regular time intervals. The τ measurements were used as input to a radiative transfer model along with AERONET retrievals of the column-integrated particle size distribution (PSD) to infer an effective imaginary part of the UV aerosol refractive index (k). This was done by fitting the MFRSR diffuse fraction measurements to the calculated values for each UV spectral channel. Inferred values of refractive index and PSD allow calculation of the single scattering albedo, ω, in the UV and comparisons with AERONET ω retrievals. The advantage of utilizing diffuse fraction measurements is that radiometric calibration is not needed for the MFRSR since the same detector measures both the total and diffuse flux. The additional advantage is that surface albedo is much smaller in the UV than in the visible spectral range and has much less effect on aerosol measurements.
A flexible algorithm to commonly process lidar and sun sky-scanning radiometer measurements is developed. The algorithm is oriented towards the engineering facilities of the radiometer CIMEL used by AERONET network and a two-to-four wavelength lidar used by European lidar network EARLINET. Numerical experiments were performed to assess algorithm sensitivity to measurement errors and possible violations of basic model assumptions.
This paper presents the methodology to process data of combined experiments using a Sun/sky scanning radiometer and a multi-frequency aerosol lidar. An algorithm is proposed to retrieve the optical properties of altitude-inhomogeneous aerosol layer reflecting both the vertical changes of atmospheric aerosol detected by lidars and the integral aerosol properties measured by ground-based Sun/sky radiometers.
Clouds play an important role in forming the atmospheric radiation budget and are a specific factor for transformation of aerosol components. Cloud composition should be correctly enough taken into account to predict operatively the light propagation trough clouds. This matter is especially of high priority near the sources of industrial pollutions. Cloud microstructure would be the most variable quantity here, because of highly-disperse soot components ingress into clouds. Such components can influence greatly on spectral absorption and reflection characteristics of cloud cover and effect globally on climate. The consistent physical approach to predict the light propagation trough clouds requires the radiative model of clouds should include a complete set of the specific optical characteristics that, according to the radiative transfer equation, are sufficient to simulate the spectral absorption and reflection of cloud cover. Different approaches can be used to determine the above specific characteristics. The most promising one is appeared to be based on the retrieval of these quantities by airborne intercloud measurements of rather a narrow set of cloud light-scattering characteristics. The main object of this report is to investigate the method for solving an inverse problem of light scattering to design a radiative model of liquid-drops clouds comprising soot components. The investigation is carried out within the scope of mathematical simulation.
The problems of optimum inversion in the presence of random noise are analyzed. Two main kinds of noise are considered: the random errors of measurements and random errors of physical model. It is studied the optimization of the numerical inverse problem solution concerning both noises. Using the statistical estimation ideas is discussed for this consideration. Specific features of every noise to influence on the limitation of information content of the optic experiment and on implementation of inversion are distinguished. The quantitative criteria to evaluate information content of input data and procedure of their interpretation are proposed. The latter is aimed to optimize the solution in presence of random errors of the model as well as errors of measurements and, moreover, to correct used model by the measurements being interpreted. An arbitrary accompanied and a priori information can be used. For example, a priori estimations of the sought and model parameters, correlations between them, non-negativity of values etc., can be included. The peculiarity of the inversion method is an essentially large number of variables and increased stability should be provided. The original iterative process of linear inversion characteristic to statistical optimizations are being proposed for this in the algorithm elaborating.
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