Using the EPIC/DSCOVR O2 B-band for monitoring vegetation

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 nm) and B-band (688 nm). The EPIC at-sensor Normalized Difference Vegetation Index (NDVI) is defined as the difference between NIR and `red' channels divided by their sum. However, the use of the O2 B-band where the vegetated surface is yet sufficiently dark instead of the `red' channel mitigates the effect of atmosphere on surface reflectance because it reduces contribution from the radiation scattered by the atmosphere. Applying the radiative transfer theory and the spectral invariant approximation to EPIC observations, the paper provides supportive arguments for using the O2 band instead of the red channel for monitoring the vegetation dynamics.