Estimation of High-Resolution Surface Shortwave Radiative Fluxes Using SARA AOD over the Southern Great Plains

Eslam Javadnia,Per Schubert,Ali Abkar

doi:10.3390/rs9111146

Abstract

Atmospheric aerosol optical depth (AOD) plays a determinant role in estimations of surface shortwave (SW) radiative fluxes. Therefore, this study aims to develop a hybrid scheme to produce surface SW fluxes, based on AOD at 1-km spatial resolution retrieved from the Simplified Aerosol Retrieval Algorithm (SARA) and several Terra MODIS land and atmospheric products (i.e., geolocation properties, water vapor amount, total ozone column, surface reflectance, and top-of-atmosphere (TOA) radiance). Estimations based on SARA were made over the Southern Great Plains (SGP) under cloud-free conditions in 2014 and compared with estimations based on the latest Terra MODIS AOD product at 3-km resolution. Validation against ground-based measurements showed that SARA-based fluxes obtain lower RMSE and bias values compared with MODIS-based estimations. MODIS-based downward and net fluxes are satisfactory, while the direct and diffuse components are less reliable. The results demonstrate that the SARA-based scheme produces better surface SW radiative fluxes than the MODIS-based estimates provided in this and other similar studies and that these fluxes are comparable to existing CERES data products which have been tested over the SGP.

Highlights

The main part of downward radiative fluxes reaching the Earth’s surface is in the range of the shortwave (SW) spectrum and consists of two components: direct and diffuse fluxes
Using radiative transmittance factors from Yang et al.’s [25] model, fluxes were estimated in two ways: firstly, by applying the Simplified Aerosol Retrieval Algorithm (SARA)-based scheme, namely based on aerosol optical depth (AOD) retrieved from SARA and ground-based measurements at the CART AErosol RObotic NETwork (AERONET) site, and secondly, by applying the MODerate-resolution Imaging Spectroradiometer (MODIS)-based scheme, namely based on the new Terra MODIS 3-km AOD
Several other Terra MODIS land and atmospheric products were used as an input to both schemes, including geolocation properties, water vapor amount, total ozone column, surface reflectance, and TOA radiance

Summary

Introduction

The main part of downward radiative fluxes reaching the Earth’s surface is in the range of the shortwave (SW) spectrum and consists of two components: direct and diffuse fluxes. The net SW radiative flux, defined as the difference between the downward and upward fluxes at the Earth’s surface, controls the total energy exchange between the atmosphere and land/ocean surface, and significantly affects climatic forming and change [1,2]. Many algorithms have been developed to estimate SW radiative fluxes at the Earth’s surface based on various remote sensing data [6,7,8,9,10,11,12,13,14,15,16,17,18]. The empirical methods establish regressions by directly linking satellite radiance data and ground-measured radiative fluxes

Objectives

Methods

Discussion

Conclusion