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We present an optimal-estimation-based retrieval framework, the microphysical aerosol properties from polarimetry (MAPP) algorithm, designed for simultaneous retrieval of aerosol microphysical properties and ocean color bio-optical parameters using multi-angular total and polarized radiances. Polarimetric measurements from the airborne NASA Research Scanning Polarimeter (RSP) were inverted by MAPP to produce atmosphere and ocean products. The RSP MAPP results are compared with co-incident lidar measurements made by the NASA High-Spectral-Resolution Lidar HSRL-1 and HSRL-2 instruments. Comparisons are made of the aerosol optical depth (AOD) at 355 and 532 nm, lidar column-averaged measurements of the aerosol lidar ratio and Ångstrøm exponent, and lidar ocean measurements of the particulate hemispherical backscatter coefficient and the diffuse attenuation coefficient. The measurements were collected during the 2012 Two-Column Aerosol Project (TCAP) campaign and the 2014 Ship-Aircraft Bio-Optical Research (SABOR) campaign. For the SABOR campaign, 73% RSP MAPP retrievals fall within ±0.04 AOD at 532 nm as measured by HSRL-1, with an R value of 0.933 and root-mean-square deviation of 0.0372. For the TCAP campaign, 53% of RSP MAPP retrievals are within 0.04 AOD as measured by HSRL-2, with an R value of 0.927 and root-mean-square deviation of 0.0673. Comparisons with HSRL-2 AOD at 355 nm during TCAP result in an R value of 0.959 and a root-mean-square deviation of 0.0694. The RSP retrievals using the MAPP optimal estimation framework represent a key milestone on the path to a combined lidar+polarimeter retrieval using both HSRL and RSP measurements.

Increasing efforts are devoted by the Ocean Color Radiometry community to explore the polarization features of the underwater light field in order to enhance possibilities for retrieving inherent optical properties (IOPs) of coastal waters. New instrumentations and data inversion algorithms are being developed to take into account the supplementary information contained in polarization data. However, estimating the Stokes vector components of the polarized water radiance from above water measurements is a challenging task, mainly because of their small magnitude and the strong contamination by the polarized sky light reflected from the sea surface. In this study, above-water measurements are used to assess the feasibility of such retrievals and their utility for retrieving IOPs. The Long Island Sound Coastal Observational platform (LISCO) near Northport, NY, was established in October 2009 to support satellite data validation. In June 2010, three customized hyperspectral HyperSAS systems (HyperSAS-POL) were added to LISCO platform enabling polarization measurements. A data processing algorithm, which includes vector radiative transfer computations, was developed and used to remove the polarization signal due to sky light reflected from the sea surface (sky glint) and derive the underwater polarization field. The spectral shape of the retrieved underwater degree of polarization was then evaluated against theoretical radiative transfer computations and in situ underwater measurements. The results confirmed the validity of the polarization measurements by the LISCO site, thus validating a continuous time series starting from the beginning of June 2010 to the present which can be used for retrievals of IOPs from polarization measurements.

We present a new approach to retrieve the aerosol properties over land that uses accurate polarization measurements over a broad spectral (410–2250 nm) and angular (±60° from nadir) ranges. The approach uses longer wavelength observations to accurately estimate the surface effects, and it is incorporated into an optimal estimation framework for retrieving the particle number density and a detailed aerosol microphysical model: effective radius, variance, and complex refractive index. A sensitivity analysis shows that the uncertainties in aerosol optical thickness (AOT) increase with AOT while the uncertainties in the microphysical model decrease. The uncertainty in the single scattering albedo (SSA) is notably less than 0.05 by the time the AOT is greater than 0.2. We find that calibration is the major source of uncertainty and that perfect angular and spectral correlation of calibration errors reduces the uncertainties in retrieved quantities. Finally, we observe that shorter wavelength (<500 nm) observations are crucial for determining the aerosols vertical extent and imaginary refractive index from polarization measurements. The retrieval approach is tested under pristine and polluted conditions using observations made by the Research Scanning Polarimeter during the Aerosol Lidar Validation experiment and over California Southern wild fires. In both cases we find that the retrievals are within the combined uncertainties of the retrieval and the Aerosol Robotic Network Cimel products and Total Ozone Mapping Spectrometer Aerosol Index. This demonstrates the unique capability of polarization measurements to accurately retrieve AOTs under pristine conditions and provide estimation of the SSA at higher AOTs.