Improving Dems Using Sar Interferometry

Interferometric synthetic aperture radar (InSAR) processing relies on phase unwrapping to convert interferometric phase to topographic height. Phase unwrapping is a di cult non-linear process that is still the subject of on-going research. Rather than processing the complete phase image to extract a digital elevation model (DEM), we use existing coarse DEMs as an integral part of the InSAR algorithm. Firstly, we estimate the baseline parameters accurately without phase unwrapping. This facilitates the removal of the coarse DEM topographic phase from the interferogram without phase unwrapping the entire interferogram. The residual interferogram after the removal of the topographic phase is generally more amenable to simple ltering and is also easier to phase unwrap. After phase unwrapping, the coarse DEM model can again be used (if needed) to constrain the baseline parameter estimates and an output InSAR DEM is produced. We apply our algorithm to both ERS Tandem Mission data and RADARSAT-1 interferometric SAR data to investigate the feasibility of using coarse DEMs in the InSAR processing algorithm. Substantial improvement is shown in the InSAR DEM quality compared to the input coarse DEMs with respect to a high quality DEM used for ground truth.