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Decorrelation mechanisms in C-band SAR interferometry over boreal forest

Temporal and spatial decorrelation effects are very important in repeat pass interferometric imaging of boreal forest. Temporal decorrelation refers to changes in the strength and distribution of scattering, due to the effects of wind, rain, and moisture changes of both canopy and ground. Spatial decorrelation is a result of baseline decorrelation, volume scattering, and uncompensated topography. These effects complicate interferometric imaging and the use of interferometry for topographic mapping of forest covered regions. The differences between heights measured from interferograms over forest and a DEM (the effective tree height) are related to the coherence. Another problem is the decrease in accuracy of coherence estimates (e.g. for land use classification) when the coherence is low. Influences of various factors on coherence in interferometry using images from the ERS-1 3 day repeat cycle of 1994 are studied. A wide range of time intervals between images and of baselines is used. The coherence of various surfaces is found to vary considerably between interferograms. As the time interval increases, the coherence generally decreases. The causes of decorrelation and their relation to meteorological effects and volume scattering are investigated. Analysis of coherence over various surfaces in Northern Sweden during the winter of 1994 is performed, with particular emphasis on forest, clear cut and agricultural areas.