Interferometric stereo radargrammetry: Absolute height determination from ERS-ENVISAT interferograms

Absolute phase determination in SAR interferometry as well as stereo radargrammetry relies on the accurate estimation of mutual range shifts (or residual delays) of SAR data pairs. If two SARs with appropriately different radar frequencies are available, baselines can be large and the regimes of interferometry and stereo radargrammetry overlap. Then radargrammetry can take advantage of the coherence of the two data sets and can employ complex speckle correlation. Hence, speckle becomes an information rather than a nuisance. In the paper the lower bound for the estimation error of residual delay is derived and compared with simulations. The result is relevant also for absolute phase determination and speckle tracking. An example for height accuracy in an ERS-ENVISAT interferometric scenario is given.