Radiometric Calibration Concept of Imaging Spectrometers for a Long-term Ecological Remote Sensing Project

The National Ecological Observatory Network (NEON), funded by the National Science Foundation, is a continental-scale ecological observation platform for discovering, understanding and forecasting the impacts of climate change, land-use change, and invasive species on ecology. An imaging spectrometer will be used by the NEON Airborne Observation Platform (AOP) to observe both the human drivers of climate change and the biological consequences of environmental change at a continental scale. To be meaningful as an ecological climate data record, the AOP data set must have a continuous and consistent calibration effort. This requires a robust calibration and validation plan to ensure data continuity from instrument-to-instrument, flight-to-flight, year-to-year, and over the 30-year lifetime of the NEON project. The NEON Imaging Spectrometer will undergo maintenance and calibration in the laboratory prior to each flight season. Laboratory calibrations include pixel-to-pixel uniformity, radiance coefficient determination, radiometric spectral response, spectral uniformity, linearity, and out of band characterization. A detector-based method will be implemented with the use of a well-characterized and extremely stable NIST traceable transfer radiometer. Solar radiation based calibrations (SRBC) will be performed during laboratory testing as an independent check. An on-board calibrator will be used in the laboratory as a side-by-side comparison during radiometric testing and as a link between laboratory and in-field measurements. Monitoring flat field imagery in-flight from the on-board calibrator and watching for changes over time will determine radiometric stability. Pre-flight calibrations in the field with SRBC and lamp-diffuser setups will allow for the monitoring of calibration drift. Laboratory calibrations will be independently tested throughout the season with vicarious calibration techniques and crosscalibration with multispectral satellite sensors. In addition to the imaging spectrometer, AOP instrumentation includes a small footprint waveform LiDAR and a high-resolution airborne digital camera. The AOP calibration plan for the NEON Imaging Spectrometers during the lifetime of the NEON project is presented.