Calibration of NEON\u27s Airborne Imaging Spectrometers

The National Ecological Observatory Network (NEON) is a continental-scale ecological observation facility currently under construction by the National Science Foundation (NSF). NEON’s mission is to enable understanding and forecasting of the impacts of land-use change and invasive species by providing the infrastructure and consistent methodologies for the collection of continental-scale ecological data. The Airborne Observation Platform (AOP) will play a unique role in scaling individual in-situ measurements collected by NEON to those collected by external satellite-based remote sensing systems. The airborne payload consists of the NEON Imaging Spectrometer, a waveform LIDAR, and a high-resolution digital camera integrated into a Twin Otter aircraft. Three payloads on separate aircraft will provide coverage of 20 NEON core sites and 40 relocatable sites as well as targets of opportunity and PI-driven science. A key component of the NEON design is the consistent calibration of the airborne instruments to provide reliable and accurate scientific data over the full lifetime of the NEON observatory. The NEON Sensor Test Facility provides the facilities for the laboratory calibration of the AOP instrumentation. This work examines the methods and facilities used to determine the radiometric and spectral calibration of the NEON airborne imaging spectrometers. The primary calibration of the NEON imaging spectrometers is conducted before and after each flight season in the NEON sensor test facility. Radiometric calibration is conducted utilizing a calibrated integrating sphere used to illuminate and calibrate all spatial pixels. A NIST traceable calibration is transferred from a NIST FEL bulb to the integrating sphere with a transfer radiometer. Comparison of the sensor output to the calibrated integrating sphere radiance is used to determine the radiometric calibration coefficients. The integrating sphere is also used to determine detector linearity and signal-to-noise. Spectral calibration is based on elemental line sources in addition to a scanning monochromator with gratings tuned to cover the solar-reflective spectral region. The spectral datasets collected are used to determine the pixel band-center and spectral response function used in the radiometric calibration. The laboratory-derived calibration is tracked throughout flight operations through the use of an on-board calibration system. The radiometric calibration of the NEON imaging spectrometer is independently verified using the vicarious reflectance-based in-situ calibration method during flight operations