Merging of the stereogrammetry and interferometry techniques as relative bandwidth grows. Illustration with VHF Carabas SAR images

SAR interferometry, requires the sensor separation to be below a critical baseline above which the coherency is lost as the ground projected frequency ranges do not overlap (frequency band shifting of one sensor -the delta-k system- is not addressed here). Indeed, as critical baseline increases with both wavelength and bandwidth, low frequency and/or wide band SAR systems have less stringent constraint for interferometric coherence, which is especially worthy for airborne acquisitions. However, as mentioned in earlier publications, the number of fringes apparent on an interferogram is (roughly) limited to twice the inverse of the relative bandwidth. Hence, wide band interferometry requires range migration evaluating for maintaining coherency, this range migration evaluation is similar to a stereogrammetric measure. As relative bandwidth grows, the two techniques merge, which can be illustrated from FOI Carabas VHF SAR data (of which the relative bandwidth is 111%).