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December 2nd, 2007
SARscape: Extending Synthetic Aperture Radar Application

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Synthetic Aperture Radar (SAR) data is providing valuable information about land use and the environment. With the arrival of new spacreborne and airborne platforms these applications are predicted to expand and grow. New processing software and techniques for SAR data are providing valuable information about weather related events, volcanic activity, seismic and subsidence activity as the list of applications grows. 

SARscape® is a focused software product designed to process SAR (Synthetic Aperture Radar) data obtained from all civil spaceborne (such as ERS-1/2, ENVISAT ASAR, RADARSAT-1, ALOS PALSAR, and TerraSAR-X-1 among others) and some airborne (OrbiSAR and E-SAR) SAR systems. This software is interfaced to ENVI®, a well-known image processing software from ITT Visual Information Solutions, and to the ArcView 3.x (ESRI® Inc.) environment. The combination provides an enhanced imagery processing environment that includes SAR support, while extending ENVI functionality. This fusion of data types places SAR within a wider GIS and image processing framework, providing a wide range of image support for decision making.

Simply looking at the amount of today operational and forthcoming (Radarsat-2, COSMO-SkyMed 2-4, RISAT-1) civil spaceborne SAR systems, it is evident that the use of SAR images is no more limited to a small research community, as in the past. Moreover, the synergetic use of these weather independent systems opens new frontiers in the domain of land and sea applications, especially with respect to those sectors, where the monitoring aspect is crucial.

sarmap – in collaboration with Privateers and AreSys – has developed SARscape – a modular set of functions dedicated to the generation of products based on airborne and spaceborne SAR data – running on Personal Computers and interfaced to ENVI (ITT Visual Information Solutions) and ArcView (ESRI Inc.) environments (see Fig. 1). A key aspect of SARscape, which includes state-of the-art algorithms, is the capability to process and combine SAR data from all past, existing, and forthcoming spaceborne systems, hence enabling to generate dedicated SAR based products containing the most complete information. Furthermore, thanks to the state-of the-art algorithms included in ENVI, the synergy between SAR products and optical ones is fully supported, making this software environment, from a remote sensing point of view, complete and powerful.

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The sarmap company has developed a set of dedicated products for TerraSAR-X-1, which are contracted by Infoterra GmbH, and has been appointed to design the processor suite for the value adding TerraSAR-X-1 processor, which was recently launched successfully and is now generating satellite imagery. CREASO GmbH owns the worldwide distribution rights for SARscape for ENVI and ArcView and therefore ensures, with the help of its cooperation partner ITT Visual Information Solutions, the availability of this advanced SAR processing software all over the world. 

What Can SARscape Do?

Synthetic Aperture Radar (SAR) systems can acquire data in different ways, such as Single or dual channel mode (for instance HH or HH / HV or VV / VH); Interferometric (single- or repeat-pass) mode; Polarimetric mode (HH,HV,VH,VV); by combining interferometric and polarimetric acquisition modes.   Obviously, different acquisition modes are subject to different processing techniques. They are:

  • Processing of SAR Intensity: The product generation is limited to the intensity processing.
  • Interferometric SAR (InSAR/DInSAR) Processing: The product generation includes intensity, and interferometric phase processing.
  • Polarimetric SAR (PolSAR) Processing: The product generation includes intensity, and polarimetric phase processing.
  • Polarimetric-Interferometric SAR (PolInSAR) Processing: The product generation includes intensity, polarimetric, and interferometric phase processing.

In order to support these processing techniques SARscape provides following customized modules which will be explained in short:

  • Basic

It includes a set of processing steps (Focusing, Multi-looking, Co-Registration, Filtering, Geocoding, Calibration, Normalization, Mosaicing, Segmentation, Classification) for the generation of SAR products based on intensity. This module is complemented by two multi-purpose tools.  

  • Focusing

It supports the focusing of RADARSAT-1, ENVISAT ASAR, and ALOS PALSAR data.

  • Gamma & Gaussian Filter

It includes a whole family of SAR specific filters. They are particularly efficient to reduce speckle, while preserving the radar reflectivity, the textural properties and the spatial resolution, especially in strongly textured SAR images. 

  • Interferometry

It supports the processing of interferometric SAR (2-pass interferometry, InSAR) and differential interferometric SAR (n-pass interferometry, DInSAR) data for the generation of Digital Elevation Models, coherence images, and land displacement / deformation maps. For this core module there are complemented modules existing, too. 

  • ScanSAR Interferometry

It offers the capabilities to process InSAR and DInSAR data over large areas (400 by 400 km).

  • SAR Polarimetry / Polarimetric Interferometry

The PolSAR/PolInSAR module supports the processing of polarimetric and polarimetric interferometric SAR data. 

  • Persistent Scatterers

The technique, extending SAR Interferometry to the analysis of large multi-temporal observations, enables to improve the measurement accuracy from few centimetres (classical Interferometry approach) to few millimetres (Persistent Scatterers approach).Note that the core modules SARscape Basic, SARscape Interferometry and the Persistent Scatterers module are standalone in the environment of ENVI or ArcView.

The other complemented modules require either the Basic or the Interferometry module. Users have full control over each of these modules, available from the SARscape drop-down menu from within ENVI. They can choose to build interactively a processing file that will then automatically process the imagery and provide e. g. focused, multi-looked, co-registered, speckle filtered, or geo-referenced final products.

A significant amount of explanation on the each function is provided within the online help that come with this software. Some users may find them quite helpful to understand the background theory. Users will find the SARscape manual “SAR-Guidebook”, which is available for free at the CREASO webpage, well written and complete, covering all aspects of SAR theory and land applications.
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Who Can Use SARscape?
This software will enable everyone with a little knowledge about the basics of SAR data to easily process any kind of SAR data and to gain reliable information. Users will need some understanding as to the end products they wish to produce, since SARscape is adaptable and can optimize processing modes for particular products.

Fields of Application
Classification can be determined using either a pixel or area based, approach, supervised or unsupervised classification. Agriculture, forestry, rice mapping, and flooding applications are prime candidates for using this software. Land cover maps, for example, can be generated using SARscape. In addition, change detection can be recorded and multi-temporal analysis can be determined (see Fig. 2).

DEM products can also be generated using SARscape. This is accomplished using the conversion of interferometric phase information. Results of differential interferometry can be deformation maps, differential interferograms and coherence images (see Fig. 3).
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Of particular interest is the possibility to use the Persistent Scatterers module because it enables to measure very small ground displacements and to trace the deformation rate related to natural or man-induced phenomena (e. g. volcanic or seismic activity, landslides, subsidence, building collapses, etc.), with excellent accuracy and spatial detail. Since optical imagery can be integrated with SAR derived products, a fusion of information combining the two data types can provide value-added information.

Mareike Kortmann is employed at CREASO GmbH, Germany.
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