IMPACTS OF DIRECTIONAL REFLECTANCE ON THE RETRIEVAL AND INTERPRETATION OF SUN-INDUCED CHLOROPHYLL FLUORESCENCE

摘要

Solar-induced chlorophyll fluorescence (ChlF) retrieval from the observed reflected radiance has attracted great interest since the ChlF is directly linked to the photosynthesis. however, ChlF estimates from the observed apparent radiance by the fraunhofer line discrimination (FLD) method are significantly affected by the directional reflectance. This study explores directional impacts on ChlF estimates by in-situ multi-angular spectral measurements. Results show that the ChlFs in both O_2-B and O_2-A absorption bands vary greatly with observing angles, and the former shows much higher sensitivity to directional reflectance than the later. Given this, a possible retrieval method using Bidirectional Reflectance Distribution Function (BRDF) models was suggested to interpret the directional effects. This study provides further insights into the characteristics of the sun-induced canopy ChlF.