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. Ten wavelength channels of calibrated radiance image data fromthe sunlit Earth are obtained every 65 min during Northern Hemispheresummer from the EPIC (Earth Polychromatic Imaging Camera) instrument on theDSCOVR (Deep Space Climate Observatory) satellite located near the Earth–Sun Lagrange 1point (L 1 ), about 1.5 million km from the Earth. The L 1 locationpermitted seven observations of the Moon's shadow on the Earth for about 3 h during the 21 August 2017 eclipse. Two of the observations were timedto coincide with totality over Casper, Wyoming, and Columbia, Missouri. Sincethe solar irradiances within five channels ( λi=388 , 443, 551,680, and 780 nm) are not strongly absorbed in the atmosphere, they can beused for characterizing the eclipse reduction in reflected radiances for theEarth's sunlit face containing the eclipse shadow. Five channels ( λi=317.5 , 325, 340, 688, and 764 nm) that are partially absorbed in theatmosphere give consistent reductions compared to the non-absorbed channels.This indicates that cloud reflectivities dominate the 317.5–780 nmradiances reflected back to space from the sunlit Earth's disk with asignificant contribution from Rayleigh scattering for the shorterwavelengths. An estimated reduction of 10 % was obtained for spectrallyintegrated radiance (387 to 781 nm) reflected from the sunlit Earth towardsL 1 for two sets of observations on 21 August 2017, while the shadow wasin the vicinity of Casper, Wyoming (42.8666 ∘  N, 106.3131 ∘  W; centered on 17:44:50 UTC), and Columbia, Missouri (38.9517 ∘  N,92.3341 ∘  W; centered on 18:14:50 UTC). In contrast, whennon-eclipse days (20 and 23 August) are compared for each wavelengthchannel, the change in reflected light is much smaller (less than 1 % for443 nm compared to 9 % (Casper) and 8 % (Columbia) during the eclipse).Also measured was the ratio REN(λi) of reflected radiance onadjacent non-eclipse days divided by radiances centered in the eclipsetotality region with the same geometry for all 10 wavelength channels. Themeasured REN (443 nm) was smaller for Columbia (169) than forCasper (935), because Columbia had more cloud cover than Casper. REN(λi) forms a useful test of a 3-D radiative transfer modelsfor an eclipse in the presence of optically thin clouds. Specific valuesmeasured at Casper with thin clouds are REN (340 nm)  =  475, REN (388 nm)  =  3500, REN (443 nm)  =  935, REN (551 nm)  =  5455, REN (680 nm)  = 220, and REN (780 nm)  =  395. Some of thevariability is caused by changing cloud amounts within the moving region oftotality during the 2.7 min needed to measure all 10 wavelength channels.

Reduction in 317–780 nm radiance reflected from the sunlit Earth during the eclipse of 21 August 2017