MISR Research Aerosol Algorithm: Refinements for Dark Water Retrievals

Abstract:

We explore systematically the cumulative effect of many assumptions made in the MISR Research Aerosol retrieval algorithm (RA), with the aim of quantifying the main sources of bias and uncertainty over ocean, and correcting them to the extent possible. We make the following corrections based on both theory and observations: (1) an ocean surface under-light model is included, and whitecap reflectance is increased for the red band, (2) physically based adjustments in particle microphysical properties and mixtures are made, (3) an adaptive pixel selection method is used, (4) spectral uncertainty is estimated from vicarious calibration, (5) minor radiometric calibration changes are made for the red and NIR wavelengths, (6) we apply a novel correction that eliminates much of the high bias in TOA reflectance (due to vignetting) when the scene has high contrast, and (7) we apply more stringent cloud screening. Validation for the RA spectral optical depths and Ångström exponents are performed against 1,132 coincident, surface-based sun photometer measurements.