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Generation of DEM with sub-metric vertical accuracy from 30' ERS-ENVISAT pairs

Claudio Prati(1) and Fabio Rocca(1)

(1) POLIMI, Piazza L. da Vinci 32, 20133 Milano, Italy


According to the spectral shift principle [1], distributed scatterers can be coherently observed by ERS and ENVISAT SAR systems despite of their carrier frequencies 30 MHz frequency shift. A 2km normal baseline should be set in order to compensate such a carrier frequency difference for almost horizontal terrain. This type of SAR interferometry configuration can be usefully exploited to get DEMs of rolling topographic features with very high vertical accuracy. A first experimental evidence has already been provided [2], [3]. The goal of this presentation is twofold: first an ERS-ENVISAT interferometric DEM of a rural area along the rivers Réveillon and Yerres (tributaries of Seine) in the immediate neighbourhood of Paris will be shown and analyzed, then the main advantages and limitations of such a system will be discussed.

This experiment has been carried out using an ERS-ENVISAT interferometric pair with a normal baseline of about 1.5km (the 30MHz frequency shift is partially compensated on cross-track terrain slopes ranging from 0 to 7 degrees) and a very short (30 minutes) temporal separation, thus containing the temporal decorrelation to acceptable values. The resulting interferogram seems very attractive in order to reconstruct high vertical precision topographic profiles (20-40 cm) suitable for characterising flood plains.

Even though the Doppler Centroid (DC) variability of ERS-2 in Zero Gyro Mode sets an additional constraint, a suitable azimuth common band filtering allows one to exploit successfully ERS-ENVISAT interferograms, as long as the DC difference is not too high (a reasonable limit could be about 1000 Hz). In our data the DC difference was found to be about 800Hz thus leaving a common band in azimuth greater than 20% of the ERS Pulse Repetition Frequency.


[1.] F. Gatelli, A. M. Guarnieri, F. Parizzi, P. Pasquali, C. Prati, F. Rocca. "The Wavenumber Shift in SAR Interferometry". IEEE Transaction on Geoscience and Remote Sensing, Vol. 32 No. 4, July 1994. [2.] N. Adam, "Das erste Cross-Interferogramm aus Aufnahmen der Radarsensoren ENVISAT/ASAR und ERS-2", available on-line at: terferogramm/_cross_interferogramm [3.] First Cross Interferogram using ENVISAT ASAR and ERS-2 SAR Radar Data, available on-line at:


Full paper

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