Repeat-pass synthetic aperture radar (SAR) interferometry provides the
possibility of producing topographic maps and geocoded as well as rad
iometrically calibrated radar images. However, the usefulness of such
maps and images depends on our understanding of how different types of
terrain affect the radar measurements. It is essential that the scene
coherence between passes is sufficient, In this paper, we derive a ge
neral system model including both radar system and scene scattering pr
operties, The model is used to interpret measurements over a forested
area where the scene coherence varies between 0.2 and 0.5. The coheren
ce is found to be sensitive to temperature changes around 0 degrees C
but surprisingly insensitive to wind speed. The interferometric height
discontinuity at the forest to open-field boundary shows good agreeme
nt with in situ tree height measurements for a dense boreal forest, bu
t is observed to decrease for a less dense forest. This suggests the p
ossibility of estimating bole volume from the interferometric tree hei
ght and a ground DEM. The decrease of scene coherence over a dense for
est with increasing baseline is also used to estimate the effective sc
attering layer thickness.