SAR interferometry with ERS-1 in forested areas

SAR interferometry relies on the coherence between two images of the same area taken from slightly different positions. Since the use of ERS-1 SAR for interferometry necessarily requires images taken at different times, so-called repeat-pass interferometry, the possible changes occurring in the target area as a function of time may reduce the coherence. This change is caused either by direct changes in the surface, or because of moving scatterers. Forested areas may lose the coherence because of strong wind or seasonal changes in the canopy. The paper presents the results from a project on the use of satellite SAR interferometry for measurement of topographic features, with particular emphasis on the effect of vegetation. The test area used is located in northern Finland, at about 67 degrees latitude, in an area mostly covered by boreal coniferous forests. The data set used consists of two images from descending orbits during the ERS-1 commissioning phase in September 1991. The images are taken at an interval of 6 days and have a baseline of 286 m. The test area gives good fringes with an average coherence of 0.5. The height accuracy is estimated to 10-15 m