Spurious Signals in TRMM/VIRS Reflectance Channels and Their Effect on Aerosol Retrievals

Abstract

Abstract Aerosol optical depths, τ1 and τ2, and the Angstrom exponent α = –ln(τ1/τ2)/ln(λ1/λ2), are retrieved from daytime measurements (sun zenith angle θo < 60°) over ocean in reflectance bands 1 (λ1 = 0.63 µm) and 2 (λ2 = 1.61 µm) of the five-channel visible and infrared scanner (VIRS) on board the Tropical Rainfall Measuring Mission (TRMM) satellite. In band 2, a thermal leak originating from the secondary spectral response peak at ∼5.2 µm contributes radiance comparable to the signal scattered by aerosols. In the past two corrections, the thermal signal was parameterized empirically as a linear function of radiances in bands 4 and 5 (centered at 10.8 and 11.9 µm, respectively), R4 and R5, and a quadratic function of view angle θ through multiple regression analyses. The regression coefficients were estimated from a limited amount of all-sky nighttime (100° < θo < 170°) data over land and ocean, and were used to predict and remove the false signal from daytime data. As a result, retrievals of τ2 and α...