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A Note on the Basic module for SAR Intensity data processing

 

There is no standard processing chain. In primis, the processing depends upon how SAR data have been acquired (acquisition modes and available SAR systems). The type of product that is envisaged determines, additionally, how intermediate SAR products (for instance terrain geocoded backscattering coefficient data) will be further processed.  

 

With respect to the first point – assuming the availability of a multi-temporal SAR raw data set –  three processing procedures can be applied:

 

1.Single-sensor, Single-mode, Multi-temporal Approach

 

This is the classical one. Multi-temporal SAR data are acquired in the same mode (for instance ENVISAT ASAR Image Mode 4). Since the geometry remains the same, following steps should be considered:

–Focusing

–Multi-looking

–Coregistration

–Multi-temporal speckle filtering (for instance De Grandi)

–Terrain geocoding, radiometric calibration and normalization

 

 

This is the most appropriate one in case of single-sensor data availability. SAR data are acquired in different geometries and thereby data acquisitions are not linked to standard repeat-pass cycle geometry (ERS-1/2 like). Since the acquisition geometry is different, following steps should be at the best considered:

–Focusing

–Generation of 1-look Intensity

–Terrain geocoding, radiometric calibration and normalization

–Multi-temporal speckle filtering (for instance Anisotropic Non-Linear Diffusion)

 

 

This is the most advanced one, since based on the principle of satellite’s constellation. SAR data are acquired in different geometries by different sensors. Therefore, data acquisitions can be optimized in terms of temporal, spatial (and spectral) resolution. In this scenario, the processing chain corresponds to the previous one. Note that particularly in this case, it is imperative that the data are accurately absolutely radiometrically calibrated.

 

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

 

Import Data

SAR data, Optical data, Digital Elevation Model, Shape data are imported either as standard or generic binary formats. The execution of this functionality is mandatory, as external data are converted into the SARscape data format .

 

Multilooking

A multi-look detected (Intensity) image is generated from Single Look Complex data by averaging the Intensity in azimuth and/or range direction.

 

Coregistration

When a multiple image data sets is acquired with the same viewing geometry, it can be coregistered in order pixels in different images to correspond with sub-pixel accuracy.

 

Filtering

The most appropriate filter can be chosen (typically depending on the application and data type) among a number of single image and multi-temporal SAR specific and generic filters.

 

Feature Extraction

Different features, which can be further used for classification purposes, are extracted from single date or multi-temporal data. They are based on first order and time-series statistics. SAR coherence (interferometric correlation) is an additional feature.

 

Geocoding, Radiometric Calibration and Normalisation

Ellipsoidal or terrain geocoding, using nominal parameters or ground control points, allows the transformation from SAR co-ordinates into a given cartographic reference system using a Range-Doppler approach. The radiometric calibration and normalisation can also be performed.

 

 

Note that:

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

–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 Basic module, available on the sarmap website, for more details on the usage and applications of the tools included in this module.

References

 

Meijering E. and M. Unser: "A Note on Cubic Convolution Interpolation", IEEE Transactions on Image Processing, Vol. 12, No. 4, April 2004.

 

Aspert F., M. Bach Cuadra, J.P. Thiran, A. Cantone, and F. Holecz: "Time-varying segmentation for mapping of land cover changes". Proceeding of ESA Symposium, Montreux, 2007.

 

Frost V.S., J. Stiles, K. Shanmugan and J. Holtzman: "A model for radar images and its application to adaptive digital filtering of multiplicative". Transactions on Pattern Analysis and Machine Intelligence, Vol. 4, No. 2, 1982.

 

Lee J.S.: "Speckle suppression and analysis for SAR images". Optical Engineering, Vol. 25, No. 5, 1986.

 

Nagao M. and Matsuyama: "Edge Preserving Smoothing". Computer Graphics and Image Processing, Vol. 9, 1979.

 

De Grandi G.F., M. Leysen, J.S. Lee and D. Schuler, Radar reflectivity estimation using multiplicative SAR scenes of the same target: technique and applications, Proceedings IGARSS, 1997.

 

Stebler O., P. Pasquali, D. Small, F. Holecz, and D. Nuesch, Analysis of ERS-SAR tandem time-series using coherence and backscattering coefficient, , Proceedings of Fringe '96 workshop, ESA SP-406, 1997.

 

Frei U., C. Graf ,E. Meier: "Cartographic Reference Systems, SAR Geocoding". Data and System, Wichmann Verlag, 1993.

 

Holecz F., E. Meier, J. Piesbergen, and D. Nüesch: "Topographic effects on radar cross section, SAR Calibration Workshop". Proceedings of CEOS Calibration Sub-Group, ESTEC, Noordwijk, 1993.

 

Meier E., Frei U., and D. Nuesch: "Precise Terrain Corrected Geocoded Images, SAR Geocoding". Data and System, Wichmann Verlag, 1993.

 

Ulaby F.T. and C. Dobson: "HandBook of Radar Scattering Statistics for Terrain". Artech House, 1989.

 

Written by Symbios under the auspices of the European Space Agency: "CEOS Earth Observation Handbook", 2008.