Assessing Band Sensitivity to Atmospheric Radiation Transfer for Space-Based Retrieval of Solar-Induced Chlorophyll Fluorescence

Xinjie Liu,Liangyun Liu

doi:10.3390/rs61110656

Abstract

In contrast to ground-based solar-induced chlorophyll fluorescence (Fs) detection, the influence of atmospheric radiation transfer is the major difficulty in Fs retrieval from space. In this study, we first simulated top-of-atmosphere (TOA) radiance using FluorMODgui3.1 and MODTRAN5 code. Based on the simulated dataset, we analyzed the sensitivities of five potential Fs retrieval bands (Hα, K I, Fe, O2-A, and O2-B) to different atmospheric transfer parameters, including atmosphere profile, aerosol optical depth (AOD550), vertical water vapor column (H2O), vertical ozone column (O3), solar zenith angle (SZA), view zenith angle (VZA), relative azimuth angle (RAA) and elevation. The results demonstrate that the Hα, O2-A and O2-B bands are the most sensitive to these atmospheric parameters. However, only the O2-A and O2-B bands were found to be sensitive to the imaging geometric parameters. When the spectral resolution was sufficient, the K I and Fe bands proved to have the best potential for space-based Fs retrieval given the current available accuracies of atmospheric products, while the O2-A band was shown to perform better at lower spectral resolutions. The band sensitivity analysis presented here will be useful for band selection and atmospheric correction for space-based Fs retrieval.

Highlights

Solar-induced chlorophyll fluorescence (Fs) refers to the emission of radiation by chlorophyll molecules
We have demonstrated that the Hα, O2-A and O2-B bands are more sensitive to atmospheric and imaging geometric parameters, while the K I and Fe bands are apparently influenced by the aerosol optical depth only
The results showed that the O2-A and O2-B bands are greatly influenced by the aerosol optical depth and imaging geometric parameters, while the O2-B band is sensitive to vertical water vapor and the ozone column

Summary

Introduction

Solar-induced chlorophyll fluorescence (Fs) refers to the emission of radiation by chlorophyll molecules. To extract Fs from measured at-sensor radiance signals, it is necessary to decouple the reflected solar flux and emitted Fs. A comprehensive overview of current methods of estimating Fs was provided by Meroni et al [7]. Most of the commonly used methods are based on the Fraunhofer Line Depth principle (FLD) [8], which compares the downward solar irradiance and the upward canopy radiance at bands inside and outside the solar Fraunhofer lines or atmospheric absorption bands. Leaf level detection of solar induced chlorophyll fluorescence by means of a subnanometer resolution spectroradiometer. An integrated model of soil-canopy spectral radiances, photosynthesis, fluorescence, temperature and energy balance. Available online: http://modis-atmos.gsfc.nasa.gov/MOD05_L2/index.html (accessed on 15 July 2014).

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