Evaluation of DEM-assisted SAR coregistration

D. O. Nitti, R. F. Hanssen, A. Refice, F. Bovenga, G. Milillo, R. Nutricato

Research output: Chapter in Book/Conference proceedings/Edited volumeConference contributionScientificpeer-review

13 Citations (Scopus)

Abstract

Image alignment is without doubt the most crucial step in SAR Interferometry. Interferogram formation requires images to be coregistered with an accuracy of better than 1/8 pixel to avoid significant loss of phase coherence. Conventional interferometric precise coregistration methods for full-resolution SAR data (Single-Look Complex imagery, or SLC) are based on the cross-correlation of the SLC data, either in the original complex form or as squared amplitudes. Offset vectors in slant range and azimuth directions are computed on a large number of windows, according to the estimated correlation peaks. Then, a two-dimensional polynomial of a certain degree is usually chosen as warp function and the polynomial parameters are estimated through LMS fit from the shifts measured on the image windows. In case of rough topography and long baselines, the polynomial approximation for the warp function becomes inaccurate, leading to local misregistrations. Moreover, these effects increase with the spatial resolution and then with the sampling frequency of the sensor, as first results on TerraSAR-X interferometry confirm. An improved, DEM-assisted image coregistration procedure can be adopted for providing higher-order prediction of the offset vectors. Instead of estimating the shifts on a limited number of patches and using a polynomial approximation for the transformation, this approach computes pixel by pixel the correspondence between master and slave by using the orbital data and a reference DEM. This study assesses the performance of this approach with respect to the standard procedure. In particular, both analytical relationships and simulations will evaluate the impact of the finite vertical accuracy of the DEM on the final coregistration precision for different radar postings and relative positions of satellites. The two approaches are compared by processing real data at different carrier frequencies and using the interferometric coherence as quality figure.

Original languageEnglish
Title of host publicationProceedings of SPIE - The International Society for Optical Engineering
EditorsLorenzo Bruzzone, Claudia Notarnicola, Francesco Posa
Place of PublicationPiscataway
PublisherSPIE
Number of pages14
Volume7109
ISBN (Print)978-0819473400
DOIs
Publication statusPublished - 2008
EventImage and Signal Processing for Remote Sensing XIV - Cardiff, Wales, United Kingdom
Duration: 15 Sep 200818 Sep 2008

Publication series

NameProceedings of SPIE
PublisherSPIE
Volume7109
ISSN (Print)0277-786X

Conference

ConferenceImage and Signal Processing for Remote Sensing XIV
CountryUnited Kingdom
CityCardiff, Wales
Period15/09/0818/09/08

Keywords

  • Coregistration
  • Digital Elevation Model (DEM)
  • Interferometry
  • Synthetic Aperture Radar (SAR)

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