<< Click to Display Table of Contents >> Navigation:  Help Content > Interferometry Module > Interferometry Module - Overview

Notes on the Interferometry module

 

This module supports the processing of:

-Interferometric SAR data (2-pass Interferometry, InSAR) for the generation of Digital Elevation Model (DEM) and related coherence.

-Differential Interferometric SAR data (n-pass Interferometry, DInSAR) for the generation of Land Displacement maps and related coherence.  

 

The following basic requirements have to be fulfilled in an interferometric pair (either for InSAR or DInSAR processing):

-Reference and Secondary data must be acquired by the same sensor. Exception to this rule is for data acquired by ERS-1, ERS-2 and ENVISAT. Indeed these sensors can be combined together in the same pair.

-Reference and Secondary data must be acquired with the same viewing geometry.

-In case of multi-polarization acquisitions, the same polarization must be selected as Reference and Secondary. It must be noted that it is possible to combine, in the same pair, a single polarization with a multi-polarization acquisition; for instance, in case of ALOS PALSAR data, we can make a pair using the HH channel of a Fine Beam Single (FBS) and the HH channel of a Fine Beam Dual (FBD).

 

Apart from the conditions mentioned above, other interferometry related parameters, such as the normal baseline and the doppler centroid difference, are suitable. These parameters, relevant to specific Interferometric pairs, are provided by the Baseline Estimation functionality.

 

Assuming appropriate data pairs, the following processing sequences are proposed:

 

1.Digital Elevation Model generation, typically includes the following steps:

 

–Flattened Interferogram Generation.

–Adaptive Filter and Coherence Generation.

–Phase Unwrapping.

–Phase Editing (if required).

–Refinement and Re-flattening.

–Phase to Height Conversion and Geocoding.

 

2.Land Displacement Mapping, typically includes the following steps:

 

–Flattened Interferogram Generation.

–Adaptive Filter and Coherence Generation.

–Phase Unwrapping.

–Phase Editing (if required).

–Refinement and Re-flattening.

–Phase to Displacement Conversion and Geocoding.

 

The following functions, included in this module, support any of the procedures above:

 

Baseline Estimation

Information related to baseline, orbital shift (in range and azimuth) and other system parameters are provided. The use of this optional functionality is exclusively to assess the InSAR pair quality. The baseline values for all possible Reference-Secondary combinations in a multi-temporal SAR acquisitions series can be extracted by using the Multi Baseline Calculation (Interferometry Tools).

 

Interferogram Generation

A multi-looked flattened interferogram is generated together with the coregistered Reference and Secondary intensity data, the original unflattened interferogram, the synthetic phase and the slant range projected Digital Elevation Model.

 

Adaptive Filter and Coherence Generation

The phase noise in the flattened interferogram is filtered and the corresponding coherence is generated.

 

Phase Unwrapping

The flattened, filtered interferogram is unwrapped in order to solve the 2π ambiguity.

 

Refinement and Re-flattening

Possible inaccuracies in the satellite orbits as well as the phase offset are corrected.

 

Phase to Height Conversion and Geocoding

The Digital Elevation Model is generated.

 

Phase to Displacement Conversion and Geocoding

The Land Displacement Map is generated.

 

Note that:

 

–SAR data must be imported (see Basic module).

–In case of SAR RAW products, the data must be imported and focussed (refer to Focusing module).

–Reference and Secondary acquisitions must remain in the same order throughout the whole interferometric processing.

–The sequence going from the Interferogram Generation to the Phase Unwrapping can be executed by means of a single "multi-step" interferometric workflow.

–Default setting for selected parameters can be specified in the Preferences panel.

–The SAR Tutorial, which includes basic knowledge on SAR theory and data processing, complements the online help.

–Data geocoded to GEO-GLOBAL cartographic reference system can be automatically displayed into the Google Earth environment by double clicking on the output .kml file.

–Co-ordinate decimal values must be entered using the dot (e.g. 29.30) and not the comma (e.g. 29,30) character.

 

Support material

Please consult the tutorial material dedicated to the Interferometry module, available on the sarmap website, for more details on the usage and applications of the tools included in this module.

References

 

InSAR Principles: Guidelines for SAR Interferometry Processing and Interpretation (ESA TM-19).

 

M. Richards: "A Beginner's Guide to Interferometric SAR Concepts and Signal Processing". IEEE Aerospace and Electronic, Vol. 22, No. 9, September 2007.

 

D. Small, P.Pasquali, and S.Fuglistaler: "A Comparison of Phase to Height Conversion Methods for SAR Interferometry". Proceedings of IGARSS 1996 – Lincoln, Nebraska – USA – 27-31 May 1996.

 

Gatelli F., A. Monti Guarnieri, F. Parizzi, P. Pasquali, C. Prati, F. Rocca, The Wavenumber Shift in SAR Interferometry, IEEE Transactions on Geoscience and Remote Sensing, Vol. 32, No. 4, 1994.