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<< Click to Display Table of Contents >> Interferometric Stacking - SBAS - Interferometric Process |
  
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<< Click to Display Table of Contents >> Interferometric Stacking - SBAS - Interferometric Process |
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Purpose
This functionality enables to execute, in an automatic way, the following processing sequence:
–Interferogram Generation and Flattening.
–Adaptive Filter and Coherence Generation.
This step is mandatory.
Technical Note
The different steps implemented here are executed using the default processing approach (consult the reference guide specific to each processing step for more details); in particular:
•The Interferogram Flattening is performed using an input reference Digital Elevation Model or the ellipsoidal model if the DEM is not inputted; the "Geometry GCP file", if entered, is used to correct the Reference image (i.e. Super Reference acquisition of the interferometric stack) onto the Digital Elevation Model. The better the reference Digital Elevation Model accuracy/resolution the better the result in terms of topography removal. It is important to note that, in case the Super Reference image has already been corrected with the manual or the automatic procedure the GCP is not needed.
•When the Connection Graph has been executed with the "Delaunay 3D" option, the unwrapped products corresponding to the connections shown in the "Time-Position Delaunay 3D plot" are marked by the _3D_upha extension.
The data multi-looking factors are relevant to the Super Reference image. In case the input SAR series contains data with different pixel sampling (e.g. ALOS PALSAR FBS and FBD acquisitions), the program automatically changes the multi-looking factors of each interferometric pair depending on its Reference acquisition mode.
After the interferogram flattening and filtering processes can optionally be added the following optional process:
•Automatic Remove Fringe Frequency polynomial. This functionality should be used with caution, the risk is to remove and loose part of the real displacement low pass components from the interferograms and from the results.
•Automatic Remove Low Pass Fringe Frequency components. This functionality should be used with caution, the risk is to remove and loose part of the real displacement low pass components from the interferograms and from the results.
•Remove a geophysical event (like an earthquake) that implies the following SBAS behavior:
✍Remove of the synthesized displacement (provided with the North, Vertical and East ground surface deformation components in meters) reprojected along the Line of Sight and converted in phase, from the interferograms crossing the event date
✍Interrupt the Atmosphere High Pass Temporal filter (second inversion) across the event date
✍Add back the synthesized displacement to the final time series
To avoid loading failures it is recommended not to move any file from its original repository folder.
After the entire interferometric process has been completed, the whole SBAS processing folder and input file list can be moved in any disk location without compromise the further processing steps.
Tandem Bistatic are accepted and correctly managed by the program.
The Delaunay 3D functionality are under maintenance.
Input Files
Auxiliary file
Reference file generated as output of the "Connection Graph" step and possibly updated afterwards. This file is mandatory.
Optional Files
Geometry GCP file
Either a previously created Ground Control Point file (.xml) is loaded (Load GCP File) or the interface to create a new Ground Control Point file is automatically loaded (Create GCP File, refer to the ""Tools>Generate Ground Control Point" for details). This file is optional.
Avoid Moving Area File
In case the areas affected by displacement are known it is suggested to create a shapefile (.shp) that contains the movement area, this shapefile must be geocoded (with the same carto-system of the reference DEM). All ScanSAR or TOPSAR bursts that intersect this shapefile will be avoided during the spectral diversity estimation phase (which would otherwise be corrupted in case of strong movements such as an earthquake). In addition, the subsequent automatic refinement steps will also take this shape into account to avoid that pixel on areas of movement are used in the refinement mask. This file is optional.
Optional Water Vapour File List
File list with water vapour data GACOS products (_filename_list.txt; *_bil; *_geo). When the list is initialized and compiled, the software will remove the water vapour component from the interferograms (*_clean_fint). A GACOS raster must be inserted for each input image (same date and time of acquisition). The couplings are made automatically by the software. This file is optional.
Classification Mask File
Geocoded geometry classified map, used to mask specific areas during SBAS processing. The masked areas will have a value of zero on the entire coherence stack and will not be considered by the unwrapping and will not be part of the final coverage map. The “Classification Mask ID List” IDs are considered as zones to be masked.
DEM/Cartographic System
Digital Elevation Model file
Name of the Digital Elevation Model file. This should be referred to the ellipsoid. This file is optional. In case it is omitted, the ellipsoidal height and the relevant cartographic reference system, must be entered.
Output Projection
In case that the Digital Elevation Model is not used, the following parameters are compulsory to define the Cartographic System:
State
Definition of the country or general projection systems.
Projection
Definition of the projection system of the selected State. In case that a general projection system is selected in State, the Projection is automatically set.
Ellipsoid
Definition of the ellipsoid. This is chosen according to the selected State and Projection.
Hemisphere
Definition of the hemisphere. This is chosen according to the selected State and Projection.
Zone
Definition of the zone. This is chosen according to the selected State and Projection.
Datum Shift Parameters
Definition of the datum shift parameters. These are chosen according to the selected State and Projection.
Reference Height
In case that the Digital Elevation Model is not used, a constant ellipsoidal height must be provided. Default Reference Height is 0.
Cartographic Parameters
The reference parameters for some projection systems (e.g. Stereographic, Polar Stereographic, Gnomonic, Mercator, Miller, Albers, etc.) can be set.
Parameters - Principal Parameters
Rebuild All
By setting this flag the whole process is started from scratch. It is advisable to leave this flag unchecked in case of process interruption, so that the products already generated have not to be computed and stored again.
Range Looks
Number of looks in range referred to the Super Reference.
Azimuth Looks
Number of looks in azimuth referred to the Super Reference.
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.
Number of Parallel Unwrapping
Defines the number of unwraps that will be performed in parallel (one interferogram for each thread). This parameter must not exceed the total number of CPU threads. The user should consider the available system memory before increasing the number of parallel processes, as the memory consumption is directly related to the number of unwraps performed in parallel.
Apply Layover and Shadow Mask
Mask the results in layover and shadow areas.
Atmosphere External Sensors
By inserting this optional list, the software removes the atmosphere artefacts from the filtered interferogram stack using external sensors such as GACOS and MERIS (only for ENVISAT data).
Atmosphere Height Correlation Flag
By setting this flag the tool estimates the residual interferometric phase component correlated to topography height (related to stratified atmosphere component in the flattened interferograms), using a the “Height Correlation Window Size [m]”. Note that the estimation of this component could remove real phase components (mostly when the correlation windows size is small) from the flattened interferograms. For this reason, this functionality should be used carefully.
Coregistration With DEM
By setting this flag, the input Digital Elevation Model is used in the coregistration process.
Unwrapping Method Type
The choice is given between the following unwrapping methods:
•Region Growing, the Region Growing unwrapping method is used;
•Minimum Cost Flow, the Minimum Cost Flow (square grid) unwrapping method is used;
•Delaunay MCF, the Minimum Cost Flow (triangular grid) unwrapping method is used.
Unwrapping Decomposition Level
The number of under sampling levels to be applied to the complex interferogram before performing the phase unwrapping can be specified (refer to the Technical Note).
Unwrapping Coherence Threshold
Pixels with coherence values smaller than this threshold are not unwrapped.
Filtering Method
The choice is given between the following filtering methods according to the default values of the filtering section of the Preferences parameters:
•Boxcar window;
•Goldstein;
•Adaptative;
•Adaptive Non Local InSAR.
Parameters - Cluster
It brings to the cluster section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.
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 - Interferogram
It brings to the interferometry section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.
Parameters - Flattening
It brings to the flattening section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.
Parameters - Filtering
It brings to the adaptive filter section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.
Parameters - Phase Unwrapping
It brings to the interferometry section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.
Parameters - Coregistration
It brings to the coregistration section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.
Parameters - Atmosphere
It brings to the atmosphere and general section of the preferences parameters. Any modified value will be used and stored for further processing sessions.
Parameters - Geophysical Model
In case of a geophysical event (like an earthquake) is present in the stack temporal coverage, the program can store it internally and use it (see Technical notes) to improve the time series estimation from this step onward.
Output Files
interferogram_stacking folder
Directory containing the following products:
•Due to the large number of output products meta (_meta). and series (.series).files are generated. They enable to load at once all relevant output products:
•The “interf_tiff” sub-folder with the tiff files of intermediate interferometric SBAS results.
Generated meta and series files:
•IS_cc_meta, IS_cc.series, which refers to all coherence images.
•IS_fint_meta, IS_fint.series, which refers to all flattened and filtered interferograms.
•IS_clean_fint_meta, IS_clean_fint.series, which refers to all flattened, filtered and cleaned (outputted by the optional processes) interferograms.
•IS_upha_meta, IS_upha.series, which refers to all unwrapped phases. Note that this same extension is used for the 2nd level unwrapped products, which are generated during the SBAS Inversion step.
•IS_pwr_meta, IS_pwr.series, which refers to all slant range power images.
•IS_ls_mask: layover and shadow mask in slant range geometry (used as permanent mask).
•IS_geo_ls_mask: layover and shadow mask in geocoded geometry.
•IS_srlia: local incidence angle map in slant range geometry.
•IS_geo_lia: local incidence angle map in geocoded geometry.
•IS_cls_mask: classification map in slant range (used as permanent mask on specific IDs).
•IS_elevation_mask: elevation mask in slant range (used as intermittent mask between the start and end month specified by the user).
work_interferogram_stacking folder
Directory used to store intermediate processing results.
In order to distinguish the input SAR pair where each output product comes from (as well as to identify it in the connection network), a prefix containing the Reference-Secondary acquisition dates (i.e. yyyymmdd) and the Reference-Secondary relationships will be added.
Specific details about 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.
References
Pepe, A., and Lanari, R. (2006): "On the extension of the minimum cost flow algorithm for phase unwrapping of multitemporal differential SAR interferograms". Geoscience and Remote Sensing, IEEE Transactions on,September 2006, 44(9), pp. 2374-2383.