Field Spectroradiometer Characterization of Solar-Induced Fluorescence to Monitor Plant Health, Estimate Carbon Flux, and Application as Ground-Truth Data

Abstract:

Solar-Induced Fluorescence (SIF) has been demonstrated to be an indicator of plant photosynthetic functioning and is proportional carbon uptake. Other indices, such as the Normalized Difference Vegetation Index (NDVI) and the Photochemical Reflectance Index (PRI) are also commonly used to monitor plant activity using remote sensing techniques. Determining the best indices for plant health, calculating carbon fixation efficiently and economically, and developing reliable ground truthing methods for satellite data will allow monitoring and comparison of regional scale carbon fluxes. In this study, spectral measurements made with a passive field spectroradiometer were used to record spectral radiances from a selection of plants in the laboratory and field. SIF is less complicated to extract under limited wavelength illumination in the laboratory. These were used to validate the Fraunhofer Line Depth Method (FLD) applied to field measurements under solar illumination. SIF, NDVI, and PRI were calculated from the spectral measurements to determine functioning of the plants and to estimate carbon fixation under both normal and water stress conditions. Previous literature and preliminary findings suggest SIF is an earlier indicator of stress and clearer estimator of carbon uptake than NDVI or PRI. Therefore, SIF is a potential monitoring index for photosynthetic activity and its retrieval with this instrument and process is desirable. We will report on the comparison of laboratory and field estimates of SIF, the evaluation of plant health indices, and the changes in SIF with stress. Given strong evidence that obtaining accurate carbon flux information via this remote sensing process is possible, this retrieval method could be reliably utilized as ground truth data for OCO2 and OCO3. In the near future, ground spectral data such as these can be combined with OCO2 data for regional monitoring and comparisons of carbon fixation, advancing carbon flux calculations and carbon-climate connections.