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 (NIS), 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 efforts at improving the spectral and radiometric calibration of the NIS in the NEON Sensor Test Facility. Recent work has focused on the traceability and uncertainty of the radiometric and spectral calibration and stability of the calibration from lab to operations. NIST FEL standards are utilized as the radiometric calibration standard and transferred to an integrating sphere through precision transfer radiometers. Wavelength calibration is tied to elemental line sources combined with a scanning monochromator to measure the spectral response functions. To verify the operational stability during acquisitions, a quality check algorithm has been developed to assess the raw NIS data prior to ingestion into the NEON processing framework. The work presented here also examines recent advances in characterizing the level of stray light in the NIS data. A first-order correction is currently being developed and tested on data acquisitions collected during normal operations to assess the impact on higher-level data products. Further research and level of effort will depend on the results of the testing