Remote sensing of solar-induced fluorescence of vegetation

Abstract

The fluorescence signal emitted from vegetation is directly linked to the photosynthesis and as such may be used as an indicator for plant functioning, stress and vitality. Observation of solar induced fluorescence from space is proposed by measuring the weak signal contribution in the Fraunhofer line wavelengths. In an ESA funded study various aspects of measuring the fluorescence signal from space have been analysed for it's feasibility. Both scientific and instrumental aspects have been considered in the analysis. The scientific requirements have been studied in detail, looking to aspects such as the selection of Fraunhofer lines, the solar induced fluorescence radiance, measurement accuracy, spatial resolution, atmosphere influence, etc. This has resulted in instrument requirements, that are the basis for a trade off study of optical observation techniques. The main choice was between applying a grating spectrometer or a filter spectrometer, each having advantages and disadvantages for Fraunhofer line detection (FLD). From both spectrometer types a preliminary optical design has been made. Besides a model has been developed to evaluate the different configurations for S/N, integration time, radiance level etc. For these calculations it appeared, that the information about solar excited fluorescence intensity of vegetation is minimal. In the study of feasibility of Fraunhofer line detection from space is demonstrated, albeit, that the observation strategy will depend on the real amount of the solar excited fluorescence intensity. The results of the study are a good basis for further development of a spaceborn Fraunhofer line detector.