The Spectral Invariant Approximation within Canopy Radiative Transfer to Support the Use of the EPIC/DSCOVR Oxygen B-band for Monitoring Vegetation

Abstract

EPIC (Earth Polychromatic Imaging Camera) is a 10-channel spectroradiometer onboard DSCOVR (Deep Space Climate Observatory) spacecraft. In addition to the NIR (780 nm) and the ‘red’ (680 nm) channels, EPIC also has the O2 A-band (764±0.2 nm) and B-band (687.75±0.2 nm). The EPIC at-sensor Normalized Difference Vegetation Index (NDVI) is defined as the difference between NIR and ‘red’ channels normalized to their sum. However, the use of the O2 B-band instead of the ‘red’ channel mitigates the effect ofatmosphere on surface reflectance because it reduces contribution from the radiation scattered by theatmosphere. Applying the radiative transfer theory and the spectral invariant approximation to EPIC observations, we provide supportive arguments for using the O2 band instead of the red channel for monitoring the vegetation dynamics