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Purpose

This panel enables to set the default processing parameters, which are used in those functions related only to interferometric (and polarimetric interferometric) processing.

Technical Note

Multilooking

This parameter is normally set with the same values as the Preferences>General; however when the baseline conditions - or topographic conditions - are such that the interferometric phase changes very fast and it eventually get lost due to an aliasing problem, a pixel over sample in range direction is required specifically for the interferometric processing. This can be achieved by entering negative multilooking values in Range direction. Actually one of the typical cases is represented by ERS-ASAR interferometric tandem pairs, which are characterized by a very small ambiguity height (hence very dense/frequent interferometric fringes); in this case the Interferometric multilooking factors shall be set to -2 and 3 (respectively in Range and Azimuth).

Here below are mentioned those steps where the "Interferometry>Multilooking" Preferences (instead of those reported in the General Preferences section) are considered for the processing:

-Coherence Generation (Basic module).

-Interferometry Module.

-Interferometric Stacking>SBAS

Decomposition Levels

The process is normally executed with the original pixel sampling (i.e. -1) or with the minimum decomposition level (i.e. 1). The use of the decomposition is intended to multilook and undersample the data in an iterative way: the interferogram is unwrapped at the lower resolution and then reconstructed back at the original resolution. The use of the decomposition can help to reduce unwrapping errors (e.g. in case of distributed low coherence areas) and it reduces the processing time and it limits the use of computer resources.

The user can specify the number of iterations (decompositions) to be executed; each iteration corresponds to an undersampling factor of 3. We suggest to avoid setting this value higher than 2.

In case of very large displacements or very steep topography (fast phase/dense fringe distribution) the use of the decomposition can cause aliasing effects. In this case the decomposition process should be avoided by setting its value to -1 or 0.

Tile Size and Overlap

These parameters, which are used only when the Minimum Cost Flow Unwrapping (with square grid only) is executed, are intended to avoid (or reduce) possible discontinuities in the unwrapped phase. These discontinuities are most probable to occur when the displacement fringe patterns are bigger (in azimuth and/or range direction) than the "Tile Size" entered here; in such case the increase of either the "Tile Size" or the "Overlap" can solve the problem. It must be noted that the processing time exponentially increases by increasing these processing parameters.

It is important to outline that:

❖If the phase image to unwrap is smaller than 4000000 pixel2 (e.g. 2000 X 2000 pixels) the program will not split it in tiles and the whole scene will be processed as a single block.

❖Tile areas larger than 4000000 pixel2 should not be used in order to avoid program failures.

Minimum Cost Coherence

This parameter is used only when the Minimum Cost Flow Unwrapping (with or without Delaunay grid) is executed. This unwrapping algorithm uses a "cost-based" system, which depends on the coherence values, to decide where it is better to locate possible phase jumps (related for instance to phase errors or aliasing problems).

This threshold it is intended to define the minimum coherence value, which is considered for the cost estimate; below this threshold a fixed cost is adopted.

Parameters - Interferometry

Interferogram Range looks

Number of looks in range direction.

Interferogram Azimuth looks

Number of looks in range direction.

Interferogram Spectral Shift Filter

The spectra of Reference and Secondary acquisitions are not completely overlapping unless the pair is acquired with zero baseline; the filter is intended to remove the part of the Reference and Secondary spectra, which are not overlapping. In case the DEM is inputted in the Interferogram Generation step, the spectral filter is adapted to the topographic local variations.

This option should always be activated. By unsetting this flag the interferogram is generated without spectral shift filter.

Interferogram Doppler Filter

This option enables to remove the portion of the azimuth spectra, which are not common between Reference and Secondary image. This is especially useful when the data pair is characterized by a large doppler centroid difference.

Interferogram Block Size

In order to speed up the processing of large files, the data are divided in blocks whose dimension is specified here in pixels. It is advised to increase this value up to 4000 in case the processing is executed on machines with large RAM (1 Gbytes or higher).

Interferogram Block Overlap

The number of overlapping pixels between adjacent blocks is specified.

Product Generation Coherence Thr

Pixels with coherence values smaller than this threshold will be set to dummy (NaN) in the generation of the following products:

- Digital Elevation Model (ScanSAR and StripMap).

- Displacement Map (ScanSAR and StripMap).

- Dual Pair Differential Interferometry (final products).

Unwrapping Coherence Phase Th

Pixels with coherence values smaller than this threshold are not unwrapped.

Unwrapping Method Type

The choice is given between the following unwrapping methods:

oRegion Growing, the Region Growing unwrapping method is used.

oMinimum Cost Flow, the Minimum Cost Flow (square grid) unwrapping method is used.

oDelaunay MCF, the Minimum Cost Flow (triangular grid) unwrapping method is used.

Unwrapping Decomposition Levels

The number of multilooking and undersampling iterations can be specified. Refer to Phase Unwrapping, Technical Notes for further information

Unwrapping MCF Tile Size in Range

Dimension of the tiles in range direction, which are processed as separate blocks when the Minimum Cost Flow Unwrapping is executed.

Unwrapping MCF Tile Size in Azimuth

Dimension of the tiles in azimuth direction, which are processed as separate blocks when the Minimum Cost Flow Unwrapping is executed.

Unwrapping MCF Range Overlap

Number of pixels, which are overlapping with the adjacent tile in range direction.

Unwrapping MCF Azimuth Overlap

Number of pixels, which are overlapping with the adjacent tile in azimuth direction.

Unwrapping MCF Minimum Cost Coherence

Coherence threshold below which a fixed cost is adopted. Reducing this threshold, the phase errors are more easily propagated to reliable phase zones. When this value is set to -1 (default setting), the "Unwrapping Coherence Threshold" specified in the relevant unwrapping processing panel (i.e. ScanSAR or StripMap) is adopted also as "Minimum Cost Coherence".

Unwrapping 3D Max Residual Height Variation

It corresponds to the maximum residual height difference (in meters) between two spatially linked pixel (2D Delaunay network). This parameter can be increased when the topographic residuals have a strong spatial variation.

Unwrapping 3D Max Disp Velocity Variation

It corresponds to the maximum displacement velocity difference (in mm/year) between two spatially linked pixel (2D Delaunay network). This parameter is considered only in the SBAS unwrapping process. This parameter can be increased when the displacement has a strong spatial variation.

Unwrapping 3D Min Valid Pairs Percentage

It corresponds to the minimum percentage of valid pairs to perform the 3D unwrapping process (3D Delaunay network). Increasing this percentage the extent of the unwrapped area will shrank.

Unwrapping 3D Height - Number of Samples

It corresponds to the number of samples, which is used to estimate the residual height variation. The higher the value the more precise the result, but the processing time increase exponentially.

Unwrapping 3D Displacement - Number of Samples

It corresponds to the number of samples, which is used to estimate the displacement velocity variation. The higher the value the more precise the result, but the processing time increase exponentially.

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.

The selected default processing parameters are loaded.

Cancel

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Specific Function(s)

None.

References

None.

Preferences specific - Interferometry

Preferences specific - Interferometry