Semi-Empirical Models for the Bidirectional Water-Leaving Radiance: An Analysis of a Turbid Inland Lake

Zeying Han,Xingfa Gu,Xin Zuo,Shuaiyi Shi,Kaiyi Bi

doi:10.3389/fenvs.2021.818557

Abstract

When a precise quantitative analysis of satellite measurements over bodies of water is required, the bidirectional effects of water-leaving radiance must be considered. The bidirectional reflectance distribution function (BRDF) is used to estimate the directional dependency of the radiance. Previous research on BRDF has focused on oceanic waters; few studies on turbid inland waters have been conducted. In this article, using multi-angle MISR measurements, five semi-empirical BRDF models (MAG2002, Lee2004, Park-Ruddick 2005, Woerd-Pasterkamp2008, and Lee2011) were quantitatively compared, and an adaptive algorithm was proposed over a typical turbid inland lake, Taihu Lake, China. Our results reveal the following: 1) the Woerd-Pasterkamp2008 and Lee2011 models provide the best fits with correlation coefficients greater than 0.8; 2) when prior modeling parameters were used, the Lee2011 model was still the most accurate with RMSEs less than 1.1%, while the accuracy of the Woerd-Pasterkamp2008 model varied; and 3) the use of an adaptive algorithm including an empirical rule based on the ratio ofbb/aimproved the accuracy. The results provide a theoretical basis for BRDF models and BRDF effects over inland Case II waters. They also providea prioriknowledge for future studies on water constituents and the quantitative inversion of atmospheric parameters.

Highlights

The spectral radiance emerging from a natural body of water is not generally isotropic (Jerlov and Fukuda, 1960)
Some achievements have been made through the comparison and validation of some of these models over clear oceanic Case I waters and coastal Case II waters, studies on turbid inland waters are lacking
Using a bidirectional reflectance database generated from space-borne MISR measurements, the model fitting accuracy of five models and the accuracy when prior modeling parameters were used were analyzed over Taihu Lake

Summary

Introduction

The spectral radiance emerging from a natural body of water is not generally isotropic (Jerlov and Fukuda, 1960). Most algorithms that attempt to retrieve the properties and constituents of water are based on in situ measurements of upwelling spectral radiance from a single viewing angle and toward the zenith (Gordon and Morel, 1983). It is common practice in ocean color remote sensing to relate the waterleaving radiance to a common geometry or account for the angular effects (Kwiatkowska et al, 2008).

Methods

Results

Discussion

Conclusion