Geostationary Chlorophyll Fluorescence Imager: Design and Preliminary Demonstration

Solar-induced chlorophyll fluorescence by terrestrial vegetation is linked closely to photosynthetic efficiency that can be exploited to monitor the plant health status and to assess the terrestrial carbon budget from space. Current optical remote sensing approaches have mainly relied on reflectance data offered by several Earth observing systems to provide estimates of potential photosynthesis rates of plant ecosystem. Another alternative approach that has been investigated for many years uses solar-induced chlorophyll fluorescence emitted by the photosynthetic process itself. This approach has the advantages over the solar reflectance one since it provides an early and more direct monitoring of the vegetation health status before any significant reduction in chlorophyll content. The chlorophyll fluorescence under solar illumination adds a weak, broad continuum to the reflected solar signals that can be detected from the filling of strong O2absorption lines or solar Fraunhofer lines. In this paper, we present the design of a tunable triple etalon Fabry-Perot imaging instrument that has the capability to provide hourly vegetation fluorescence measurements from a geostationary satellite based on high resolution solar reflected spectra of several key solar Fraunhofer lines. The preliminary observational results obtained in the laboratory will also be shown to demonstrate the Geo sensing technique, prototype instrument performance, and fluorescence measurement capability.