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Effect of atmosphere in InSAR over Kuwait Desert

Hala K Al Jassar(1) and K. S. Rao(2)

(1) Kuwait University, P. O. Box:5969,, Safat 13060, Kuwait
(2) Kuwait University, P. o. Box No:5969, Safat 13060, Kuwait

Abstract

In spite of numerous advantages of SAR Interferometry such as generating very high resolution and accurate Digital Elevation Model (DEM), mapping of surface displacement vectors due to earthquake, land subsidence etc., the technology suffers severely due to atmospheric effects. There are certain models to correct for the atmospheric effects with the knowledge of the distribution of water vapor and other parameters. However, these models are not very accurate and the required inputs are seldom available, particularly for places like Kuwait Desert.

The aim of the present study is to assess the extent of atmospheric effects on SAR Interferometry over Kuwait Desert for DEM as well as land subsidence study. Under ESA sponsored project (C1F-3807), we received so far 20 ASAR scenes of ENVISAT for Kuwait study area. The baselines are computed for all the combinations using EoliSA and GAMMA Interferometry software packages. The data has been screened out based on its baseline. The data sets suitable for DEM (with baselines varying from 100 m to 300 m) and for subsidence study ( with baselines varying from 5 m to 70 m) are sorted out.

Some of the data sets that are suitable for DEM generation has an interesting combination. Multiple DEMs are possible to generate with the same master image, but changing the slave image with different baseline and temporal durations. Since the master image is the same for these DEMs, it will be easy to compare the DEMs for its quality. GAMMA software is used for the Interferometry processing and ERDAS image processing package is used for the analysis of the data.

About 200 control points were identified for the quantitative comparison of Elevation values derived from different DEMs generated through InSAR. It is interesting to note that the correlation is very high only over the oil fields and protected areas. The correlation is very poor over the open desert regions even for 35 days repeat passes. Elevation values are extracted for all the control points from the InSAR DEMs as well as SRTM DEM for absolute and relative comparisons. The RMS error with reference to SRTM DEM varies from 2 m to 10 m. No correlation of the RMS error either with baseline or with coherence was noticed. However, the coherence found to vary inversely (linearly) with day difference.

Using ERDAS image processing package, different DEMs with same master image are subtracted to study the spatial distribution of change in the DEM. The difference is very much dependent on the spatial location and varies randomly from one set to another set of DEMs. The results are presented in terms of figures and tables. The results clearly indicate the presence of atmospheric effects on InSAR technology over Kuwait desert. -------------------- The authors are thankful to Kuwait University for Sponsoring the research work undet the project code: SP 04/06

 

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