Uncertainty Budget of the Airborne Imaging Spectrometer APEX

ESA’s Airborne Imaging Spectrometer APEX (Airborne Prism Experiment) was developed under the PRODEX (PROgramme de Développement d\u27EXpériences scientifiques) program by a Swiss-Belgian consortium and entered its operational phase at the end of 2010 (Schaepman et al., 2015). Work on the sensor model has been carried out extensively within the framework of the European Metrology Research Program as part of the Metrology for Earth Observation and Climate (MetEOC and MetEOC2). The focus has been to improve laboratory calibration procedures in order to reduce uncertainties, to establish an uncertainty budget for both laboratory calibration and in-flight cases, and to upgrade the sensor model to compensate for sensor specific biases. In this contribution we present the APEX traceability chain, which comprises various sources of uncertainty. These include the spectral and radiometric equipment of the calibration laboratory but more importantly also sensor model components that deal with artefacts caused by environmental changes and electronic features, namely (a) the impact of ambient air pressure changes on the radiometry in combination with dichroic coatings (Hueni et al., 2014), (b) influences of instrument baffle and optical base plate temperatures on the radiometry, (c) spectral smearing and binning effects of the Visible/Near-infrared detector , and (d) electronic anomalies causing radiometric biases in the four shortwave infrared detector readout blocks. The sensor model and its related uncertainties are the result of laboratory and in-flight experiments carried out over the course of several years. All calibration and characterisation data have been entered into a purpose built calibration information system (Hueni et al., 2013), comprising half a terrabyte of data at this stage. This contribution also includes a brief introduction to this system as it forms the information technology basis for all the work that has led to the end-to-end uncertainty model. Hueni, A., Lenhard, K., Baumgartner, A., Schaepman, M., 2013. The APEX (Airborne Prism Experiment - Imaging Spectrometer) Calibration Information System. IEEE Transactions on Geoscience and Remote Sensing 51(11), 5169-5180. Hueni, A., Schlaepfer, D., Jehle, M., Schaepman, M. E., 2014. Impacts of Dichroic Prism Coatings on Radiometry of the Airborne Imaging Spectrometer APEX. Appl. Opt. 53(24), 5344–5352. Schaepman, M., Jehle, M., Hueni, A., D\u27Odorico, P., Damm, A., Weyermann, J., Schneider, F. D., Laurent, V., Popp, C., Seidel, F. C., Lenhard, K., Gege, P., Küchler, C., Brazile, J., Kohler, P., Vos, L. D., Meuleman, K., Meynart, R., Schläpfer, D., Itten, K. I., 2015. Advanced radiometry measurements and Earth science applications with the Airborne Prism Experiment (APEX). Remote Sensing of Environment 158, 207-219