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DIFFERENTIAL INSAR STUDIES IN THE BOREAL FOREST ZONE IN FINLAND

Kirsi Karila(1) and Juha Hyyppä(1)

(1) Finnish Geodetic Institute, P.O. Box 15, FIN-02431 Masala, Finland

Abstract

In this paper we present preliminary results on the applicability of differential SAR interferometry to detect and measure land movement in the vegetated areas where only a few targets or small areas maintain coherence. Strong temporal decorrelation in the vegetated areas makes traditional DINSAR impracticable and, therefore, techniques that are based on phase values of single pixels and long time series should be applied.

The study area is located on the southwest coast of Finland (22°35’E, 60°15’N). The area consists mostly of forest and fields but it also comprises cities of Turku, Salo and Hanko and several small settlements. Related to the INSAR research there are two interesting phenomena in the study area. Firstly postglacial land uplift of a few millimeters per year is known to take place in the area. And secondly, since the center of Turku has been built on clay soil there occurs subsidence of many buildings.

The data set consists of 24 ERS SAR images from 1992-2002. Weather data provided by Finnish Meteorological Institute were used in the selection of SAR acquisitions. A new precise leveling, to be completed in 2004, will be used as a reference data for the land uplift study.

Altogether 23 differential interferograms were generated and the analysis on the amount of coherent targets was carried out. Coherent targets or permanent scatterers can be found throughout the study area: buildings, cliffs and rocky islands in Turku archipelago. Preliminary analysis of the phase values has shown that there is remarkable phase noise present in the data. The phase data should be corrected for possible atmospheric effects and orbital errors in order to get deformation data. First we must investigate further whether the coherent target density is high enough for permanent scatterers analysis. And secondly more data will be acquired to get more reliable results. Preliminary results of the long-term phase values are presented in this paper.

 

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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