Traceability of the hyperspectral satellite for monitoring and remote sensing of the Earth (EnMAP)

The reference radiation source of the hyperspectral satellite for the remote sensing of the Earth (EnMAP) has been calibrated at PTB with high resolution in the wavelength range from 400 nm to 2500 nm. This will ensure the long-term comparability and traceability of its global measurement data from the fields of geobiology, geochemistry and geophysics.

The Environmental Mapping and Analysis Program (EnMAP) is a German satellite mission that is equipped with a hyperspectral camera for the global remote sensing of the Earth (http://www.enmap.org). This mission's objective consists in measuring environmental data for geobiology, geochemistry and geophysics based on spatially and spectrally highly resolved datasets in the wavelength range from 400 nm to 2500 nm. These data will provide accurate information about parameters such as land cover, biodiversity, water quality and raw materials, thus also allowing statements about the consequences of climate change and 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 HSI during the course of the mission.

At PTB, the radiance of the reference radiation source has been determined with spectral and spatial resolution. 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 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). The RTS 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.

Contact:

C. Monte, 7.32, E-Mail: Christian.Monte(at)ptb.de