Shortwave Reflected Energy from NISTAR and EPIC onboard the DSCOVR Spacecraft

We compare the total reflected shortwave energy from the NISTAR instrument (Electrical substitution radiometer) with an estimate of the shortwave reflected energy product from the Earth Polychromatic Imaging Camera (EPIC) - both are onboard the Deep Space Climate Observatory (DSCOVR). This new shortwave reflected energy product uses 6 narrow-band wavelengths from 340 to 780nm. Additional hyperspectral information is provided by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) and the SCIAMACHY instrument. We sifted through the many AVIRIS flights and selected nadir viewed spectra from a small number (~10) of homogeneous scenes (e.g. solid cloud scene with 100% cloud fraction; cloud-free ocean, cloud-free forest, cloud-free desert). Our method assumes that the spectra from a given EPIC pixel is a weighted combination of the spectra from the solid cloud scene and one of the cloud-free spectra. We use the VLIDORT (Vector LInearized Discrete Ordinate Radiative Transfer package) to account for differences in viewing and illumination geometry.

The total area-weighted reflected shortwave energy from an entire EPIC image is compared with the Band B Shortwave reflected energy from NISTAR. Our analysis from March to December 2017 shows the two are highly correlated with differences ranging from -10 to 10 Watts m-2. But over the entire time period the EPIC estimate is, on average, only 2-3 Watts m-2 below the NISTAR product.