Retrieval of Ocean Color Products From Multi-angle Polarimeter Measurements
Abstract
Reliable estimation of the contribution of absorbing aerosols (pollution or dust) to the top-of-atmosphere (TOA) signal is difficult, but important in order to retrieve accurate ocean color products. A vector radiative transfer model (VRTM) for the coupled atmosphere-ocean system was used to investigate whether an imager-type spectroradiometer like MODIS, currently flying onboard the Aqua and Terra satellites, could detect absorbing aerosols if they could measure the linear polarization of the light, that is, the Q Stokes parameter in addition to the total radiance I. Accurate VRTM simulations in conjunction with an optimal estimation scheme were used to retrieve three aerosol parameters: aerosol optical depth at 869 nm, optical depth fraction of fine mode (absorbing) aerosols at 869 nm, and aerosol vertical location. Both fine and coarse mode aerosols were assumed to be bimodal, each with a lognormal size distribution, located either between 0 and 2 km or between 2 and 4 km in the atmosphere. From simulated data, we found that by itself the total radiance I at the nine MODIS VIS channels was generally insufficient to accurately retrieve all three aerosol parameters (about 15% to 37% success rate). But by adding the Q Stokes component it was possible to retrieve values of aerosol optical depth at 869 nm to within 0.03, single-scattering albedo at 869 nm to within 0.04, and vertical location in about 65% of the cases. The retrieval algorithm uses neural networks to overcome the computational burden of VRTM computations to accurately simulate TOA total and polarized radiances, enabling optimal estimation techniques to exploit information from multiple channels. Therefore, such an algorithm could, be readily implemented for operational retrieval of aerosol and ocean products from moderate or hyperspectral polarimeters. Retrievals of ocean parameters from simulated multi-angle polarimeter data generated by the coupled atmosphere-ocean VRTM will also be discussed.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMOS11D1438L
- Keywords:
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- 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSESDE: 3339 Ocean/atmosphere interactions;
- ATMOSPHERIC PROCESSESDE: 4264 Ocean optics;
- OCEANOGRAPHY: GENERALDE: 4275 Remote sensing and electromagnetic processes;
- OCEANOGRAPHY: GENERAL