The Automated SAR Ortho-rectification Software System enables users of synthetic-aperture-radar (SAR) data to form processed images that are free of the distortion caused by the SAR imaging geometry and topography. The software consists of four modules:

  • FOCUS™, a program for automated formation of SAR images;
  • PHASE™, a complete package of software for interferometry;
  • RadarStereo™, a stereoscopic-image-processing program; and
  • OrthoSAR™, a package of software for automated terrain and geometry correction and geocoding of SAR image data.

The disadvantage of SAR satellite data is that heretofore, images obtained by processing the data have been distorted by the peculiar imaging geometry of SAR systems and by topography. However, SAR can provide information that is not obtainable by other imaging techniques. Because SAR is unaffected by clouds, digital elevation models (DEMs) can always be obtained by use of stereoscopic SAR. Furthermore, because SAR is a coherent imaging technique, accurate DEMs can be obtained by use of interferometry; these accurate topographic models can be used by OrthoSAR™ to remove from imagery the distortion due to topography and imaging geometry.

Techniques for processing SAR image data, including techniques for processing data from stereoscopic and interferometric SAR, and techniques for ortho-rectification, existed before the development of the present software. However, there were no commercial-grade software systems for stereoscopy and ortho-rectification, and there was no integrated system that performed all of these functions.

The principal novelty of this software is the integration, into one easy-to-use package, of all of the software packages needed to process SAR data, including the processing to extract DEMs and the distortions due to imaging geometry and topography. The modules were designed and implemented in an object-oriented manner so that they can easily be upgraded as new techniques or new data sources become available. The software system was constructed to be operated through a Java™ graphical user interface, which can also be easily changed and upgraded as needed.

FOCUS™ is fully automated, can be used to process data from all current SAR satellite missions, and can easily be modified to work with data from future missions. The software is able to take advantage of multi-processor architectures and is significantly faster than previously available software designed for the same purpose.

PHASE™ can be used to create DEMs with vertical errors of less than a meter (depending on the quality of the data). In the displacement-map mode, PHASE™ can be used to detect tectonic movement or subsidence of the ground to a sensitivity of less than a centimeter. While the software affords much flexibility in process control, including choice among different algorithms for several of the necessary tasks, it remains easy to use. A particular advantage of the software is that a crude DEM, perhaps one that was created with RadarStereo™, can be ingested to aid in the production of a more accurate, refined DEM.

RadarStereo™ is fully automated and uses novel techniques for the registration of images and generation of tie points. It also uses a novel algorithm for calculating stereoscopic solutions from radar parameters.

OrthoSAR™ is also fully automated, and, unlike other ortho-rectification software packages, it uses the radar equations to perform corrections. OrthoSAR™ can optionally produce a mask of regions where imagery is compromised by layover or by shadow.

Significant interest in this integrated software system has been expressed by persons in universities and laboratories who wish to use the software to create DEMs to study motion and deformation of the ground. Some features of this software are also being marketed as part of a comprehensive radar ground station, with great success. OrthoSAR™ and RadarStereo™ are also available as parts of a popular geographic-information software system, ERDAS Imagine™.

This work was done by Grant R. Burkhart of Vexcel Corp. for Stennis Space Center. For further information, please contact Ron McCoy, (303) 444-0094, extension 229.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to

Vexcel Corporation
22477 55th Street
Suite 201
Boulder, CO 80301

Refer to SSC-00108, volume and number of this NASA Tech Briefs issue, and the page number.


NASA Tech Briefs Magazine

This article first appeared in the October, 2001 issue of NASA Tech Briefs Magazine.

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