EPIC Spectral Observations of Variability in Earth's Global Reflectance.

Weidong Yang,Alexander Marshak,Tamás Várnai,Yuri Knyazikhin

doi:10.3390/rs10020254

Abstract

NASA’s Earth Polychromatic Imaging Camera (EPIC) onboard NOAA’s Deep Space Climate Observatory (DSCOVR) satellite observes the entire sunlit Earth every 65 to 110 min from the Sun–Earth Lagrangian L1 point. This paper presents initial EPIC shortwave spectral observations of the sunlit Earth reflectance and analyses of its diurnal and seasonal variations. The results show that the reflectance depends mostly on (1) the ratio between land and ocean areas exposed to the Sun and (2) cloud spatial and temporal distributions over the sunlit side of Earth. In particular, the paper shows that (a) diurnal variations of the Earth’s reflectance are determined mostly by periodic changes in the land–ocean fraction of its the sunlit side; (b) the daily reflectance displays clear seasonal variations that are significant even without including the contributions from snow and ice in the polar regions (which can enhance daily mean reflectances by up to 2 to 6% in winter and up to 1 to 4% in summer); (c) the seasonal variations of the sunlit Earth reflectance are mostly determined by the latitudinal distribution of oceanic clouds.

Highlights

The Earth Polychromatic Imaging Camera (EPIC) is a ten-channel earth monitoring spectroradiometer onboard the Deep Space Climate Observatory (DISCOVR) satellite located at Sun–Earth Lagrange-1 (L1) point
The resolution of EPIC images depends on the viewing zenith angle (VZA), and is the highest at the point where the viewing zenith angle is 0◦
We report on EPIC observations of the global reflectance of the whole globe in individual channels, and on their daily and seasonal variability

Summary

Introduction

The Earth Polychromatic Imaging Camera (EPIC) is a ten-channel earth monitoring spectroradiometer onboard the Deep Space Climate Observatory (DISCOVR) satellite located at Sun–Earth Lagrange-1 (L1) point (http://epic.gsfc.nasa.gov) From this unique location it is able to observe the entire sunlit face of Earth continuously. The resolution of EPIC images depends on the viewing zenith angle (VZA), and is the highest at the point where the viewing zenith angle is 0◦ This point is called the sub satellite point, where a straight line from a satellite to the center of the Earth intersects the Earth’s surface. We discuss the mean and the variability of reflectances observed over ocean and land separately, and show their latitude dependence These observations from individual channels provide preliminary, yet helpful information to better understand variations of global reflectance and Earth radiation balance.

Data and Methods

Results

Conclusions