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ROSES Proposals

Evaluation of UV Atmospheric Correction in the Presence of Absorbing Aerosols, and Quantification of Enhancements Provided by Multiangle, Polarimetric and Oxygen A-Band Observations

PI: Olga Kalashnikova - NASA Jet Propulsion Laboratory
Satellite remote sensing of ocean color is an invaluable tool for assessing the productivity of marine ecosystems and monitoring changes resulting from climatic or environmental influences. Yet water-leaving radiance comprises less than 10% of the signal measured from space, making correction for absorption and scattering by the intervening atmosphere imperative. Traditional ocean color algorithms are based on a standard set of aerosol models and the assumption of negligible water-leaving radiance in the nearinfrared. Modern improvements have been developed to handle absorbing aerosols such as urban particulates in coastal areas and transported desert dust over the open ocean, where ocean fertilization can impact biological productivity at the base of the marine food chain. Even so, imperfect knowledge of the absorbing aerosol optical properties or height distribution results in well-documented sources of error. At short wavelengths, where PACE spectrometry intends to improve the separation of chlorophyll from CDOM as well as quantify different phytosynthetic pigments contributing to light absorption spectra, these problems are amplified due to the increased Rayleigh and aerosol optical depth, especially at off-nadir view angles. This proposal is to the Atmospheric Correction category of the PACE Science Team. Through sensitivity studies and simulated retrievals employing both Mie and nonspherical particle scattering codes in conjunction with a vector Markov Chain radiative transfer code, we will quantitatively evaluate the relative merits of various measurement modalities for meeting the PACE Science Definition Team uncertainty requirements of max (5%, 0.001) in water-leaving reflectance in the visible and max (10%, 0.002) in the near-UV. In particular we will quantify water leaving radiance measurement uncertainty in the presence of absorbing aerosols from ultraviolet observations at single view angles representative for the PACE ocean color spectrometer. Then we investigate the added value of observations from (a) multiangle UV radiometry, (b) multiangle visible photopolarimetry, and (c) oxygen A-band for simultaneous characterization of absorbing aerosol microphysical properties, effective altitude, and non-zero water-leaving radiance. Bio-optical models will be used to characterize surface bidirectional reflectances. Theoretical sensitivities will be then evaluated against AirMSPI observations at AERONET-OC UC SeaPrism site collected during PODEX, SEAC4RS, and HyspIRI campaigns. Measurements by TOMS, OMI, and JPL's airborne sensor AirMSPI demonstrate the importance of UV observations for detecting absorbing aerosols. Theoretically, multiangle UV radiometry, blue wavelength polarimetry, and narrowband (~5 nm) oxygen A-band measurements have the potential to estimate aerosol height. Our experience with MISR demonstrates the ability of multiangular radiances to distinguish dust from other airborne particles, and shows the value of such observations for separating aerosol and surface scattering over non-black ocean waters. Polarimetry offers additional constraints on aerosol size distribution and real refractive index. Drawing upon our expertise in aerosol remote sensing instrumentation and associated aerosol and surface retrieval algorithm development for MISR, AirMSPI, and AirMSPI- 2, we will refine the requirements for a PACE imager with multiangular, UV-shortwave infrared, A-band, and polarimetric sensing capability (the polarimeter), assess the practicality of the required observations, and quantify the added value of imaging polarimeter to the PACE ocean color spectrometer in compensating for the effects of absorbing aerosols.