Three-Pass DInSAR (InSAR operator) | ![]() |
Three-pass DInSAR, stands for three-pass differential interferometry. It is a method to remove the topographic induced phase from an interferogram that contains topographic, deformation, and atmospheric components.
This step can be performed only if an unwrapped topography interferogram (topo pair) and a complex deformation interferogram (defo pair) are present. Both defo and topo pair has to be referenced to a a common master. This can be achieved by processing a stack of interferograms in NEST-DORIS. Both defo and topo interferograms have to be corrected for the phase, and sampled on the same grid (see Coregistration and Wrap Operator). Also, both defo and topo interferograms must have the same multilook factors and the same dimensions (i.e. overlap exactly).Recommendation is that the perpendicular baseline of the topo-pair should be larger than that of the defo-pair. This ratio is recommended in order to prevent that noise is "blown up". Of course, this geometry cannot be always controlled, and it rather depends on the available data.
This operation is performed in the stack processing tree. First create a stack of interferograms, that coregistered to the same master and processed until subtraction of the reference phase. Then we have to unwrap defo-pair. In order to do so, the deformation pair has to be selected, and extracted for the external unwrapping in the Snaphu software. After the unwrap is performed externally, the unwrapped results are imported back into the NEST. Finally, for DInSAR operators, both defo-pair and topo-pair are listed as a source products, and the output of the operator is a differential intereferogram.
To geocode the differential phase values, standard geocoding modules of NEST can be applied.
This operator performs without any parameters, all the necessary processing information is constructed using product metadata. The only input parameter is the control flag for the degree of the orbit interpolator.
Source Products are stack of:
Output Bands are stack of differential interferograms. The amplitude is the same as that of the original 'deformation' interferogram. A complex value (0,0) indicates that for that pixel unwrapping was not performed correctly.
(More details on algorithmic implementation COMING SOON!)