To deliver high quality data sets to the user community, space sensors have to be calibrated with high accuracy. Besides pre-launch and on-board calibration, there exists the possibility to inter-compare the sensor data using well-characterized ground sites. To cover different radiometric signal levels, ground sites with high and low spectral reflectance (and surface temperatures) were chosen to allow not only an absolute signal comparison, but also an estimation of the linearity of the sensor signal. This why one ground site is located at in the dark ocean (East china sea), and the other is a fresh snow site in the polar region (alternating: Arctic and Antarctic cal sites). These polar sites have the advantage to compare sensors from different sun-synchronous orbit satellites platforms on the same day, i.e. semi-simultaneous measurements can be performed.
The dark ocean site will be located near Ishigaki Island (Japan) at 24°37'N and 123°27'E using optical buoy data and frequent in-situ measurements. The snow target sites are in the Antarctic and Arctic, where measurements will be carried out in the polar autumn and spring near Syowa Station (East Ongul Island, Lützow-Holm Bay, East Antarctica; 69°S and 39°35'E) and near Barrow (Alaska, USA; 71°16'N, 156°50'W).
In the scope of the project the ground sites will be characterized (depending on logistical and weather conditions), to allow an estimation of the TOA signal, which will be calculated using either developed codes or generated products. After systematic (space sensor and ground-truth) data acquisition and analysis, a comparison between these space sensors will be provided to assess long-term variations and trends in the calibration.
This paper describes the ongoing preparation (e.g., data selection, ground truth measurements and algorithm development) for a systematic inter-sensor comparison of the GLI and MERIS/AATSR sensors, which are onboard of ADEOS-2 and ENVISAT satellites.