Atmospheric Correction of AISA Measurements Over the Florida Keys Optically Shallow Waters: Challenges in Radiometric Calibration and Aerosol Selection

Abstract

An Airborne Imaging Spectrometer for Applications (AISA) hyperspectral imager was deployed on a manned aircraft flown at 1305-m altitude to collect data over optically shallow waters in the Florida Keys with the ultimate goal of mapping water quality and benthic habitats. As a first step, we developed a practical atmospheric correction (AC) approach to derive surface remote-sensing reflectance ( ${{\bm{R}}_{{\bm{rs}}}}$ ) from AISA measurements using radiative transfer simulations and constraints obtained from field spectral ${{\bm{R}}_{{\bm{rs}}}}$ measurements. Unlike previously published method, the AC approach removes the surface Fresnel reflection and accounts for aircraft altitude and nonzero near-infrared (NIR) reflectance through iteration over the pre-established look-up tables (LUTs) based on MODTRAN calculations. Simulations and comparison with concurrent in situ ${{\bm{R}}_{{\bm{rs}}}}$ measurements show the feasibility of the approach in deriving surface ${{\bm{R}}_{{\bm{rs}}}}$ with acceptable uncertainties. The possibility of errors in the radiometric calibration of AISA is demonstrated, although a definitive assessment cannot be made due to lack of enough concurrent in situ measurements. The need for noise reduction and the difficulty in carrying out a vicarious calibration are also discussed to help advance the design of future AISA missions.