Abstract
The Deep Space Climate Observatory (DSCOVR) through the earth polychromatic imaging camera (EPIC) continuously observes the illuminated disk from the Lagrange-1 point. The EPIC sensor was designed to monitor the diurnal variation of ozone, clouds, aerosols, and vegetation, especially those features that benefit from observation near-backscatter conditions. The EPIC sensor does not contain any onboard calibration systems. This study describes the inter-calibration of EPIC channels 5 (0.44 µm), 6 (0.55 µm), 7 (0.68 µm), and 10 (0.78 µm) with respect to Aqua-MODIS and NPP-VIIRS. The calibration is transferred using coincident ray-matched reflectance pairs over all-sky tropical ocean (ATO) and deep convective cloud (DCC) targets. A robust and automated image-alignment technique based on feature matching was formulated to improve the navigation quality of the EPIC images. The EPIC V02 dataset exhibits improved navigation over V01. As the visible channels display similar spatial features, a single visible channel can be used to co-register the remaining visible bands. The VIIRS-referenced EPIC ATO and DCC ray-matched calibration coefficients are within 0.3%. The EPIC four-year calibration trends based on VIIRS are within 0.15%/year. The MODIS-based EPIC calibration coefficients were compared against the Geogdzhayev and Marshak 2018 published calibration coefficients and were found to be within 1.6%.
Highlights
The Deep Space Climate Observatory (DSCOVR) [1] satellite was launched on 11 February 2015 and arrived at the Lagrange point 1 (L1) point on 8 June 2015
The NASA DSCOVR-earth polychromatic imaging camera (EPIC) imager L1B data V01 products were available between June 2015 and July 2017, whereas the V02 data were analyzed between June 2015 and October 2018
The EPIC imager is well suited to continuously observe the sunlit portion of the Earth, to provide retrievals benefitting from backscatter conditions and to study the diurnal variation of clouds and other retrievals
Summary
The Deep Space Climate Observatory (DSCOVR) [1] satellite was launched on 11 February 2015 and arrived at the Lagrange point 1 (L1) point on 8 June 2015. The DSCOVR satellite, having both sun- and earth-viewing sensors, orbits the sun and has the same orbital period as the Earth. This positioning allows the earth polychromatic imaging camera (EPIC) sensor to continuously view the sunlit portion of the Earth [2]. EPIC and geostationary (GEO) full-disk images provide similar Earth views. The GEO full disk image, is always centered at the equator and never captures Earth’s imagery poleward of ±70◦ latitude. The orbital configuration of DSCOVR in the L1 position is such that EPIC cannot view the entire sunlit side of the Earth. As a consequence of its position, EPIC acquires the Earth-view measurements under near backscattering conditions with a scattering angle between 168.5◦ and 175.5◦
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