RESAMPLE

In this chapter the resampling, or interpolation, of the slave image on the master grid is described. The slave image is resampled (reconstruction of original signal from the samples by correlation with interpolation kernels in space domain) accordingly to the transformation model from the step COREG_PM and optionally DEMASSIST. This model states with sub-pixel accuracy which points of the slave correspond to the master grid.

Note: This step may be fairly time consuming.

The spectrum in azimuth can be centered at zero before resampling, and shifted back to its original Doppler centroid frequency afterwards. This is required since the spectrum of the kernel function is centered at zero. See also [7]. This shifting has been implemented in release 3.0, but not in prior versions.

The polynomial described by the strings in the slave result file (Xtrack_f_DC_constant, etc.) is used. If the spectrum should be shifted, use the card RS_SHIFTAZI.

New in v3.4 is that the azimuth kernel is shifted to the Doppler centroid, not as before the dataspectrum to zero and back. This is made default.

To assess the quality of the resampling, the resampled slave image can again be coregistered (step FINE) onto the master. This should yield offset vectors that are normally distributed with zero mean. The slave image could also be resampled in steps, first resampling it by a first degree model, then again with a higher degree model.