The Bonn experiment

Taking advantage of the 3-day repeat orbit during the first ice phase of ERS-1, 19 corner reflectors (CR) were installed along an approximately straight line of 15 Km length in a relatively flat and homogeneous area west of Bonn.

The ERS-1 SAR image shows the position of some corner reflectors placed in the area. The corner reflectors were constructed in such a way as to allow a vertical lifting.

From the 19 CRs only 2 had been lifted during the period in question. A vertical lifting of 1 cm was actually done at each, and this movement has been estimated using the SAR differential interferometry technique with an error of 1-2 mm.

This figure shows the spatially averaged phase difference measured for the corner reflector N. 11 (left side) and N. 13 (right side).

The corner reflectors have been moved between the satellite passages of the 23rd of March and the one of the 26th of March, and this is visible in the phase difference, comparing the phase differences between 23 and 29 and between 26 and 29 of March.

The experiment proved that the sensitivity of differential interferometry is in the sub-cm range, at least for point targets.

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry