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Full scene (100 x 100 km) ERS Tandem interferogram colour composite of Zurich area

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  • Satellite: ERS-1/ERS-2
  • Instrument: SAR
  • Country: Switzerland
  • Acq.dates: 4,5/11/95 at 22.33
  • Fucino, Italy
  • Size: 645 kb

This full scene (100 x 100 km) interferometric composite image from the ERS-1/ERS-2 covers the Lake of Constance (Bodensee) in the upper right of the scene, the oblong Lake of Zurich just below the image centre and the Lake of Lucerne (Vierwaldstaettersee) in the lower left corner. The upper part of the scene consists of a gentle hilly terrain while the image bottom is already part of the pre-alpine mountain chaines. North is approximately towards the top of the page. The colour composite was generated using red for the coherence, green for the phase difference between the two data sets and blue for the radar backscatter intensity.

High coherence is indicated by the red. The presence of the green component indicates that the phase is noisier, resulting in lower coherence. Fringes in red/yellow are therefore of good quality for phase unwrapping while red/green fringes indicate reduced quality. Fringes are visible also on the flat land because the flattening was not perfectly performed by the interferometric quicklook prototype processor at ESRIN. The slight loss in phase coherence between the two dates is visible in the fringes as a shift from red/yellow to red/green, especially towards the south and the east within the scene. This loss of coherence may have been caused by snow showers in the night of the 5th.

A threshold was applied to the coherence (<0.2), assigning all low coherence image parts to blue, green and black. Blue indicates high intensity regions such as forested areas in the hills and layover zones in the mountains, but also watersurfaces which were rough only on one of the two days. Black indicates still water surfaces and radar shadows or areas with high incidence angles on the back-slopes.

Overall, there are extensive regions in this image where the interferogram is of sufficient quality for the terrain topography to be derived. The forested mountain slopes of the lower part of the image are of generally lower coherence but the full resolution image indicates that even in these regions fringes are present. (Data processed by ESA/ESRIN)

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