Interferometric Synthetic Aperture Radar has the capability to provide the user with the 3-D-Information of land
surfaces. To gather data with high height estimation accuracy it is necessary to use a wide interferometric baseline or a
high radar frequency. However the problem of resolving the phase ambiguity at smaller wavelengths is more critical than
at longer wavelengths, as the unambiguous height interval is inversely proportional to the radar wavelength. To solve
this shortcoming, a multiple baseline approach can be used with a number of neighbouring horns and an increasing
baselength going from narrow to wide. The narrowest, corresponding to adjacent horns, is then assumed to be
unambiguous in phase. This initial interferogram is used as a starting point for the algorithm, which in the next step,
unwraps the interferogram with the next wider baseline using the coarse height information to solve the phase
ambiguities. This process is repeated consecutively until the interferogram with highest precision is unwrapped. On the
expense of this multi-channel-approach the algorithm is simple and robust, and even the amount of processing time is
reduced considerably, compared to traditional methods. The multiple baseline approach is especially adequate for
millimeterwave radars as antenna horns with relatively small aperture can be used, while a sufficient 3-dB beamwidth is
The paper describes the multiple baseline algorithm and shows the results of tests on real data and a synthetic area.
Possibilities and limitations of this approach are discussed. Examples of digital elevation maps derived from measured
data at millimeterwaves are shown.