Feasibility of Estimating Cloudy-Sky Surface Longwave Net Radiation Using Satellite-Derived Surface Shortwave Net Radiation

Yamin Guo,Jie Cheng

doi:10.3390/rs10040596

Abstract

Surface longwave net radiation (LWNR) is a vital component in the surface radiation budget. Major progress has been made in the estimations of clear-sky LWNR. However, the estimation of cloudy-sky LWNR remains a significant challenge. In this paper, a linear model (LM) and a multivariate adaptive regression spline (MARS) model were developed to estimate the cloudy-sky LWNR from a satellite-derived surface shortwave net radiation product. Spatially and temporally matched satellite data and ground-measured LWNR, which was collected at 24 sites from four networks, were used to build and validate the linear and MARS models. The effects of land cover, climate type, and surface elevation on the estimate of LWNR were also analyzed. The MARS model, incorporating the normalized difference vegetation index (NDVI) and surface elevation (H) as the inputs, had the best performance. The determination coefficient, BIAS, and root mean square error (RMSE) were 0.51, 0.01 W/m2, and 26.10 W/m2, respectively. The developed model, when combined with freely distributed Global LAnd Surface Satellite (GLASS) products, showed promise for producing surface LWNR and all-sky surface net radiation.

Highlights

Surface net radiation plays a fundamental role in determining atmospheric and oceanic thermal conditions and circulations, which shape the main characteristics of the earth’s climate
Surface net radiation is the sum of shortwave net radiation and longwave net radiation (LWNR) [4], which can be expressed by the following equations: Rn = RnS + RnL, (1)
The purpose of this paper is to investigate the feasibility of estimating LWNR under cloudy-sky conditions using a remote sensing surface shortwave radiation product

Summary

Introduction

Surface net radiation plays a fundamental role in determining atmospheric and oceanic thermal conditions and circulations, which shape the main characteristics of the earth’s climate. Surface net radiation is the sum of shortwave net radiation and longwave net radiation (LWNR) [4], which can be expressed by the following equations: Rn = RnS + RnL, (1) RnS = RSd − RSu, (2) RnL = RLd − RLu, (3). Where Rn is the surface net radiation, RnS is the shortwave net radiation, RnL is the LWNR, RSd is the shortwave downward radiation, RSu is the shortwave upward radiation, RLd is the longwave downward radiation, and RLu is the longwave upward radiation. LWNR is a key component in the surface radiation budget. Accurate estimates of surface longwave radiation are required for calculating surface net radiation—especially at night. This, in turn, controls all of the surface energy budget components, including latent heat flux [5,6]

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