Solar-Induced Chlorophyll Fluorescence Measured From an Unmanned Aircraft System: Sensor Etaloning and Platform Motion Correction

A dual-field-of-view spectroradiometer system has been developed for measuring solar-induced chlorophyll fluorescence (SIF), from an unmanned aircraft system (UAS). This “AirSIF” system measures spectral reflectance in the visible and near-infrared wavelengths as well as SIF in far-red O2-A and red O2-B absorption features at high spatial resolution. It has the potential to support the interpretation and validation of canopy-emitted SIF observed by airborne, and future spaceborne sensors at coarser spatial resolutions, as well as simulated by radiative transfer models. In this contribution, we describe the AirSIF data collection and processing workflows and present a SIF map product of spatially explicit and geometrically correct spectroradiometer footprints. We analyze two possible sources of error in SIF retrieval procedure: a sensor-specific spectral artifact called etaloning and the uncertainty of incoming irradiance during UAS flight due to airframe motion (pitching and rolling). Finally, we present results from two SIF acquisition approaches: a continuous mapping flight and a stop&go flight targeting predefined areas of interest. The results are analyzed for a case study of Alfalfa and grass canopies and validated against ground measurements using the same system.