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Traceable geodesic data

Reference radiation source for remote sensing of the Earth calibrated

PTB-News 3.2019
Especially interesting for

geophysics, geobiology, geochemistry

remote sensing of the Earth

climate research

At PTB, the reference radiation source of the EnMAP satellite for the remote sensing of the Earth has been calibrated with high resolution. This ensures the long-term comparability and traceability of its global measurement data from the fields of geobiology, geochemistry and geophysics.

The OBCA mounted next to the transfer standard on the translation system at PTB's Reduced Background Calibration Facility 2. (Photo credit: Fraunhofer IOF, CYMER)

The Environmental Mapping and Analysis Program (EnMAP) is a German satellite mission for the global remote sensing of the Earth. For this purpose, a hyperspectral camera collects spatially and spectrally highly resolved data in the wavelength range from 400 nm to 2500 nm which are used to measure environmental data. They provide accurate information about parameters such as land cover, biodiversity, water quality and raw materials, which allow statements about the consequences of climate change or local environmental disasters.

For the radiometric and spectral traceability of the spectral data measured by means of the Hyper Spectral Imager (HSI), a combination of a solar reflector and an additional reference radiation source is used on board the satellite. This reference radiation source, the On-Board Calibration Assembly (OBCA), is to ensure in particular the radiometric and spectral stability of the Hyperspectral Imager during the course of the mission.

In cooperation with the manufacturer of this device, OHB System AG (Bremen und Oberpfaffenhofen), the radiance of the reference radiation source was determined with spectral and spatial resolution at PTB. In this context, a radiometric measurement uncertainty of 2 % at a spectral resolution of 0.1 nm had to be achieved in the whole wavelength range to be calibrated from 400 nm to 2500 nm. In order to comply with the critical service life limitations (amounting to 40 hours for the halogen lamps and 100 h for the LEDs of the OBCA), PTB developed a calibration procedure based on the spectral comparison with a radiometric transfer standard (RTS). Calibration was carried out by means of the new Reduced Background Calibration Facility 2 (RBCF2) for the first time. The transfer standard itself is traced to primary standards of PTB. Both the qualification model and the flight model of the OBCA have been successfully calibrated within the limits of the required measurement uncertainties.

The RBCF2 is currently being used in further applications, among other things for the traceability of the FORUM instrument within the scope of the Earth Explorer 9 Mission of the European Space Agency (ESA).


Christian Monte
Department 7.3
Detector Radiometry and Radiation
Phone: +49 30 3481-7246
Opens window for sending emailchristian.monte(at)ptb.de