Topographic mapping of forested areas in the
western Great Lakes region using spaceborne synthetic aperture radar interferometry.
Jonathan Ward Chipman - 2001
[UMI Proquest Full
Synthetic aperture radar (SAR) interferometry represents
a new method for topographic mapping. Experimental L-band (24 cm wavelength)
interferometric SAR images from the second Shuttle Imaging Radar-C (SIR-C)
mission in October 1994 were used to produce a digital elevation model (DEM)
covering 2100 km2 in northwestern Wisconsin. In
non-forested areas this DEM has an accuracy of 3.5 m RMSE. In forested areas,
there is a bias in the interferometric elevation estimates, such that the
interferometric phase centers appear to be above (or in some cases, below)
the ground surface. These biases are dependent upon forest type and structural
characteristics. Models were derived to predict the interferometric elevation
biases in red pine plantations based on mean stem diameter, for thinned and
non-thinned stands (R2 of 0.88 and 0.72 respectively).
In addition, the relationship between interferometric elevation biases and
image-based characteristics such as SAR image backscatter magnitude, image
texture, and normalized difference vegetation index (NDVI) were examined.
While L-band backscatter is loosely correlated with interferometric elevation
biases, the other variables were not found to be good predictors. To ensure
that end-users are aware of the presence of spatially variable biases in
interferometric DEMs, it is recommended that such DEMs be accompanied by
pixel-level maps showing expected error magnitudes, taking into account differences
in accuracy between forested and non-forested areas.