All-sky total and direct surface Shortwave Downward Radiation (SWDR) estimation from satellite: Applications to MODIS and Himawari-8

Abstract

The earth’s surface shortwave downward radiation (SWDR), which is generally defined as the sum of the incoming solar energy over the earth’s surface in the shortwave spectrum (0.3–3.0 μm), is a key component of the surface radiation budget (SRB). Spatiotemporally continuous SWDR is needed because it is one of the required parameters driving many land models and applications. In this study, a look-up table (LUT)-based, easy-to-use approach to derive all-sky total and direct surface SWDR is proposed. The only inputs for the new approach include solar and observing angles, blue band radiance, elevation, and surface climatological albedo. The applications of the new method to both Moderate Resolution Imaging Spectrometer (MODIS) and Himawari-8 measurements are presented, and validation versus ground measurements from 21 sites shows that both the instantaneous and daily SWDR can be accurately derived from the above-mentioned method. A further comparison with the Himawari-8 L2 SWDR product reveals that our newly proposed method performs better, with an overall root mean square error (RMSE) of 91.77 (13.99) W/m2 and a bias of −3.91 (-1.55) W/m2 for the instantaneous (daily) total SWDR. The simplicity and reliable accuracy of the new approach make it suitable for producing all-sky surface total and direct SWDR from space-based measurements at the globe scale.