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Purpose

 

This panel enables to set the default processing parameters, which are used in those functions where the coregistration process is executed.

 

Technical Note

 

The coregistration consists of spatially register two or more images with sub-pixel accuracy. In case of SAR Intensity products this process is initialised using the satellite orbital parameters and then optimized by means of a cross-correlation based function. In case of Single Look Complex data the coregistration shift estimate is further refined (1/100th of pixel accuracy) by automatically selecting a series of image "chips" throughout the image, where "mini-interferograms" are calculated.

 

The cross-correlation process is based on the following consecutive steps:

 

Orbit Accuracy

This setting enables to check the accuracy of the coregistration polynomial, which is only based on the orbital parameters. If this check evidences orbital errors, then the first shift estimate is performed by means of the cross-correlation on a large "central window" and the orbit based initialisation is automatically disabled.

 

Window Size        

In case of small data sets (i.e. few hundred pixels in range and azimuth direction), the default window size must be reduced accordingly.

 

Reject Threshold        

The shift polynomial, which is based on the interferometric coherence, is compared with the cross correlation shift polynomial (refer to the "Cross-correlation Grid" mentioned below). If the standard deviation or the root mean square error results higher that this threshold, the coherence based shift is discarded and the cross correlation shift (refer to the "Fine Shift Parameters" mentioned below) is adopted.

 

 

Parameters - Coregistration

 

Number Coefficient Range

The number of coefficients (from 1 to 6) used for the coregistration polynomial, in range direction, is set. It makes sense to have this value set to 4 especially in case of squinted geometry or using large baseline. It is suggested to use values lower or equal to 3 in case of small data subsets (1000 pixels or less in range direction).

Δrange = K1 + K2X + K3Y + K4X2 + K5Y2 + K6XY

 

Number Coefficient Azimuth

The number of coefficients (from 1 to 6) used for the coregistration polynomial, in azimuth direction, is set. It makes sense to have this value set to 4 especially in case of squinted geometry or using large baseline. It is suggested to use values lower or equal to 3 in case of small data subsets (1000 pixels or less in azimuth direction).

Δazimuth = K1 + K2X + K3Y + K4X2 + K5Y2 + K6XY

 

Number Residual Coefficient Range

The number of coefficients (from 1 to 5) used for the residual coregistration polynomial (i.e. after the shift estimated from the Digital Elevation Model), in range direction, is set.

Δrange = K1 + K2X + K3Y + K4X2 + K5Y2

 

Number Residual Coefficient Azimuth

The number of coefficients (from 1 to 5) used for the residual coregistration polynomial (i.e. after the shift estimated from the Digital Elevation Model), in azimuth direction, is set.

Δazimuth = K1 + K2X + K3Y + K4X2 + K5Y2

 

Border Distance Range

Pixel co-ordinate, in range direction, corresponding to the upper left corner of the grid of windows used for the fine coregistration (cross-correlation and coherence based) process.

 

Border Distance  Azimuth

Pixel co-ordinate, in azimuth direction, corresponding to the upper left corner of the grid of windows used for the fine coregistration (cross-correlation and coherence based) process.

 

Skip Coregistration

By setting this flag the input data are not coregistered. This option is considered only for Tandem-X data.

 

 

Initialization from Orbits

By setting this flag the orbital parameters (and the Digital Elevation Model if this is provided as input) are used for a preliminary shift estimate. This flag must be checked when the coregistration process is performed using the input DEM.

 

Initialization from Amplitude        

By setting this flag the shift estimate, which has been initialized from the orbits (if the relevant flag has been checked), is improved by using a cross-correlation approach on the Reference/Secondary(s) Intensity images.

 

Initialization from Coherence        

By setting this flag the shift estimate, which has been computed from the orbits and/or the amplitude data (if one or both the relevant flags have been checked), is improved by means of the interferometric coherence. Note that this option is possible only when Single Look Complex data are inputted.

 

Orbit Interpolation

It represents the multiplying factor, which is used to calculate the orbit position at sub pixel level in azimuth direction. The higher the value the longer the processing time and the accuracy. Values higher then 10 are typically not required.

 

Cross-correlation Central Window

 

Initial Range Window Size        

Range dimension, in pixels, of the large "central window".

 

Initial Azimuth Window Size        

Azimuth dimension, in pixels, of the large "central window".

 

 

Cross-correlation Grid

 

Range Window Number

Number of windows, in range direction, which are used for the cross-correlation process.

 

Azimuth Window Number

Number of windows, in azimuth direction, which are used for the cross-correlation process.

 

Range Window Size        

Range dimension, in pixels, of the "small windows".

 

Azimuth Window Size        

Azimuth dimension, in pixels, of the "small windows".

 

Cross Correlation Threshold        

If the correlation value is below this threshold, then the window is not used for the shift estimate.

 

Fine Shift Parameters

 

Oversampling Fine

In case the fine shift estimate, which is based on the coherence (mini-interferograms), fails - or in case of Intensity data - a cross-correlation based function is applied on over sampled data. The higher this value the longer the processing time and the accuracy. Values higher then 16 are typically not required.

 

Range Window Number Fine

Number of windows, in range direction, where the fine shift is estimated.

 

Azimuth Window Number Fine

Number of windows, in azimuth direction, where the fine shift is estimated.

 

Range Window Size Fine

Range dimension, in pixels, of the windows where the fine shift is estimated.

 

Azimuth Window Size Fine

Azimuth dimension, in pixels, of the windows where the fine shift is estimated.

 

SNR (Signal to Noise Ratio) Threshold        

If the interferometric Signal to Noise value is below this threshold, the window is not used for the coherence based (mini-interferograms) fine shift estimate. The relationship between the Signal to Noise Ratio (SNR) value and the coherence (γ) value is:

 

SNR = γ2/1-γ2

Oversampling Coherence

In order to retrieve the highest coherence values, an optimal shift is calculated by "moving" the Secondary data with steps equal to the inverse of this value. The higher the value the longer the processing time and the accuracy. Values higher then 4 are typically not required.

 

Reject Threshold        

If the difference between the cross correlation and the coherence based polynomia is higher than this threshold, the coregistration shift is computed on the basis of the cross correlation only (refer to the "Cross Correlation Oversampling" mentioned above).

 

Coregistration With DEM

The input will be coregistered with the provided Digital Elevation Model.

 

 

General Functions

 

Load Preferences

It allows loading specific Preferences tthirteen different settings  as possible alternative default processing values.

 

Load

It allows loading an .xml, .sml or .txt file where SARscape common Preferences where previously saved.

 

Save

It allows saving SARscape common Preferences for a future processing using the same preferences characteristics.

 

Help        

Specific help document section.

 

 

Ok        

The selected default processing parameters are loaded.

 

Cancel        

The window will be closed.

Specific Function(s)        

 

None.

 

References

 

None.