A Snapshot Imaging System for the Measurement of Solar-Induced Chlorophyll Fluorescence-Addressing the Challenges of High-Performance Spectral Imaging

This article introduces a novel stereo-camera system for the measurement of solar-induced chlorophyll fluorescence (SIF) at 760 nm. The instrument uses optical interference filters to gain high background radiation-suppression in the telluric oxygen absorption band at 760 nm, to measure the weak SIF signal. Featuring spatially high-resolution images and a lightweight setup, the system was built for ground- and drone-based field applications. The technical setup of the device and the used methodology are presented as well as a theoretical performance simulation, indicating a maximal reduction of the background radiation by a factor of five. The experimental results show that steady-state fluorescence can be measured with signal-to-noise ratios (SNRs) between 5 and 10, depending on the saturation level of the sensor and the aperture settings of the lens. Intensity changes lower than 0.2 mWm(-2)sr(-1)nm(-1), emitted by a calibrated light emitting diode (LED) reference panel, can be reliably distinguished under direct sun illumination. The system's capability to detect fast changes in photosynthetic dynamics, with both high spatial and temporal resolution, is demonstrated by a video sequence of a leaf during a dark-light transition. In a static, platform-based operation, the classification of fluorescent and nonfluorescent surfaces under natural conditions is presented.