First validation of Earth Reflector Type Index (p) parameter from DSCOVR EPIC VESDR data product using Terrestrial Ecosystem Research Network observing sites in Australia

The spectral invariants theory predicts that amount of radiation scattered by a canopy in a given wavelength is a simple function of the leaf albedo and a spectrally invariant parameter p. This study provides the first assessment of p parameter obtained from the Earth Reflector Type Index (ERTI) provided in Deep Space Climate Observatory (DSCOVR) Earth Polychromatic Imaging Camera (EPIC) Vegetation Earth System Data Record (VESDR) product. Our results suggest that ERTI parameter can possibly deliver information about photon recollision probability, albeit with a risk of lower accuracy, even for conditions that differ from the original assumptions in the spectral invariants theory (non-reflecting soil, dense canopies). We verified the expected link between ERTI p parameter in the EPIC VESDR product, foliage clumping, and canopy cover with empirical data. Importantly, this was done with study sites in Australia that included types of forests that are still relatively unexplored with spectral invariants theory. Our findings contribute to understanding product uncertainty and spatial representativeness of the in situ measurements from the Terrestrial Ecosystem Research Network (TERN) SuperSites in Australia.