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27.05.2005 14:43 Age: 12 Jahre

Paris: ERS-ENVISAT Interferometry

Figure 1: ERS-Envisat Interferogram

Figure 2: ERS-Envisat Coherence Product

Paris ERS-ENVISAT Interferometry
At baselines around 2 km ERS2 - ASAR-IS2-VV interferograms show coherence when the effect of the 31 MHz carrier frequency difference is compensated by the slightly different look direction. In the example shown the overlap  of both the range spectra and the azimuth spectra (instability of ERS2) is only partial. At this large baseline a 10 m height difference causes already a full topographic phase cycle. Consequently, the differential interferogram is noisy for the urban areas (Paris is located in the northern part of the area covered) and forest. For tilted surfaces the applied range common band filtering is not appropriate. For the agricultural areas an overall consistent, relatively smooth, phase surface is found. The phase features visible are most likely related to spatial variations in the atmospheric water vapor.

Figure 1: Differential interferogram, one color cycle corresponds to one phase cycle; the image intensity corresponds to the average backscattering coefficient; shown in Lambert Conical Conformal Projection at reduced spatial resolution. ERS2, ASAR raw data courtesy CAT1_2452; processing Gamma Remote Sensing.

Figure 2: ERS2 - ASAR Coherence product. Red-green combination of ERS2 - ASAR Coherence (red channel, linear scale 0.0 - 1.0) and average backscattering (green channel, log scaling). Blue channel is not used. Green (uncorrelated = low red) areas correspond to water, forests, and tilted surfaces (low coherence due to combination of non-overlapping range spectra). Orange -yellow colors correspond to agricultural fields. Urban areas appear predominantly in green (uncorrelated due to vertical dimension of buildings) but include small areas and points with high coherence; shown in Lambert Conical Conformal Projection at reduced spatial resolution. ERS2, ASAR raw data courtesy CAT1 2452; processing Gamma Remote Sensing.