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Purpose

 

The SAR signal processor can use the full synthetic aperture and the complete signal data history in order to produce the highest possible resolution, albeit very speckled, Single Look Complex (SLC) SAR image product. Multiple looks Intensity images may be generated by averaging over range and/or azimuth resolution cells. For an improvement in radiometric resolution using multiple looks there is an associated degradation in spatial resolution.

 

Technical Note

 

Two multilooking methods are available, one performed at time domain (default) and another at frequency domain. Time domain multilooking consist of the application averaging windows to reduce the speckle while frequency domain implementation spits the spectrum in sublooks and the averages them.

 

The advantage of frequency domain multilooking is that it may achieve a better ENL (equivalent number of looks) at the same spatial resolution but at the same time being computationally more demanding.

 

The number of looks is a function of pixel spacing in azimuth, pixel spacing in slant range, and incidence angle. The goal is to obtain in the multi-looked image approximately squared pixels considering the ground range resolution (and not the pixel spacing in slant range) and the pixel spacing in azimuth. In order to avoid over- or under-sampling effects in the geocoded image, it is recommended to generate a multi-looked image corresponding to approximately the same spatial  resolution foreseen for the geocoded image product. The ground resolution in range is defined as:

 

       ground range resolution = pixel spacing slant range

                                               sin(incidence angle)

 

Example

ERS-1/2 Single Look Complex data are processed with the following parameters:

 

 

 

This information is available in the _slc.sml file in the following fields:

 

[Processing section]PixelSpacingAz

[Processing section]PixelSpacingRg

[ChannelInfo section]LookAngle

 

This information is available in the _slc.sml file in the following fields:

 

[Processing section]PixelSpacingAz

[Processing section]PixelSpacingRg

[ChannelInfo section]LookAngle

 

The multi-looking factors in range and azimuth will be:

 

➔ground resolution = 7.90 / sin(23°) = 20.21 m, corresponding to 1 look in range.

➔A similar resolution in azimuth is obtained by applying a multi-looking factor of 5 (pixel spacing azimuth multi-looked  = 3.99 . 5 =19.95 m).

 

Input Files

 

Input Files:

Input file name:

•Single Look Complex (_slc). Note: it is converted in intensity (_pwr) image.

•Slant range (_pwr) intensity

•Ground range (_gr) data

 

Parameters - Principal Parameters

 

Multilooking Method

Time or frequency domain where the multilook should be performed.

 

Range looks        

Number of looks in range.

 

Azimuth looks        

Number of looks in azimuth.

 

Grid Size for Suggested Looks

The grid size, in meters, used to tune range and azimuth looks. If the other parameters are manually set, the grid size will not imply a change in their values.

 

Parameters - Global

 

It brings to the general section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.

 

Parameters - Other Parameters

 

It brings to the general section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.

 

Output Files

 

Output file list

Output file name(s) of the multi-looked Intensity data. This file list is mandatory.

 

_pwr        

Multi-looked slant range Intensity image and associated header files (.sml, .hdr).

 

_pwr.xml        

Xml file containing the geographic co-ordinates of the scene corners.

 

_pwr.shp        

Shape file and associated header files (.sml, .hdr) containing the image perimeter in geographic co-ordinates.

 

_pwr.kml       

ASCII file containing the image perimeter in geographic co-ordinates. Double clicking on this file will automatically position the boundaries of the scene into the Google Earth environment.

 

_par.sml        

Xml file containing temporary processing parameters.

 

 

Details specific to the Units of Measure and Nomenclature of the output products can be found in the Data Format section.

 

General Functions

 

Exec

The processing step is executed.

 

Store Batch        

The processing step is stored in the batch list. The Batch Browser button allows to load the batch processing list.

 

Close        

The window will be closed.

 

Help

Specific help document section.

 

 

Specific Function(s)

 

None.

 

 

See Also

 

Task, SARscapeBatch object, SARscapeBatch script example

 

References

 

None.