|
<< Click to Display Table of Contents >> Interferometry - Dual Pair Differential Interferometry |
  
|
|
<< Click to Display Table of Contents >> Interferometry - Dual Pair Differential Interferometry |
|
Purpose
This functionality is an extension of the 3-pass and the 4-pass differential interferometry approaches. The products (in slant range and geocoded geometries) are represented by displacement map (in slant range direction) and height measurements.
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 Generation is performed without using input Digital Elevation Model for the coregistration process.
–The Interferogram Flattening is performed using an input reference Digital Elevation Model or the ellipsoidal model. In case of inaccuracy in the satellite orbits or in the Digital Elevation Model geolocation, a Ground Control Point (i.e. "Geometry GCP file") is required to correct the SAR data (i.e. Reference acquisition of the interferometric pair) with respect to the reference Digital Elevation Model. If two different Reference images are used (4-pass approach), the GCP file must be created using the "Reference 1" as "Reference file"; note that the pixel used as GCP must be imaged by both "Reference 1" and "Reference 2" acquisitions. The GCP is not needed if the manual or the automatic correction procedure has been previously executed on the Reference(s) acquisitions.
SAR data must be acquired by the same sensor with the same acquisition geometry (i.e. same incidence angle).
The output products consist of:
–Displacement velocity (if the "Linear Model" flag is checked) measured in mm/year.
–Displacement (if the "Linear Model" flag is not checked) measured in millimeters.
–Precise surface elevation measurement. This is obtained by summing the residual heights (_height), which are derived from the interferometric technique, to the input Digital Elevation model. The unit of measure is meters.
–Interferometric coherence images.
–Flattened and filtered interferograms.
–Unwrapped phase images.
The displacement values are reported with:
–Positive sign if the movement corresponds to a decrease of the sensor-to-target slant range distance.
–Negative sign if the movement corresponds to an increase of the sensor-to-target slant range distance.
All intermediate processing results and parameters are stored in the "Root Name_dual_work_dir" folder, which is created in the output directory. This folder can be removed only whether no more processing iterations have to be executed for a specific input data set.
Depending on the input files, a 3-pass or a 4-pass approach is implemented:
–When the "Input Reference 2 file" is not inputted, the 3-pass approach is implemented and the "Input Reference 1 file" will be the Reference for both the "Input Secondary 1 file" and the "Input Secondary 2 file".
–When the "Input Reference 2 file" is inputted, the 4-pass approach is implemented and the "Input Reference 1 file" will be the Reference for the "Input Secondary 1 file", while the "Input Reference 2 file" will be the Reference for the "Input Secondary 2 file". It is worthwhile to note the "Resampling" method, which is set among the input parameters, is used for the coregistration of the 2nd pair onto the 1st.
When the "Linear Model" flag is checked, which means that a linear displacement can be assumed, the displacement velocity (mm/year) as well as the height estimate is computed from the two interferometric pairs.
When the "Step Model" flag is checked, the same (or very similar) displacement is expected in the two interferometric pairs. This model is typically used to generate the displacement map related to abrupt deformations (e.g. earthquakes), when two "post-displacement" acquisitions are available. The displacement figures are provided in millimeters.
When the "No Model" flag is checked, the "Input Reference 1/Input Secondary 1" pair is supposed not to be affected by displacement, which is actually measured (in millimeters) from the "Input Reference 1/Input Secondary 2" pair (3-pass) or from the "Input Reference 2/Input Secondary 2" pair (4-pass).
The "Input Reference 1/Input Secondary 1" pair is used in this case for the height estimate; thus this is supposed to be a "good quality" InSAR pair for DEM generation.
The Linear Model solves the following equation system:
Phase1 = (Hres*K1) + (V*T1*4π/λ)
Phase2 = (Hres*K2) + (V*T2*4π/λ)
The Step Model solves the following equation system:
Phase1 = Hres*K1 + (D*4π/λ)
Phase2 = (Hres*K2) + (D*4π/λ)
The No-Model solves the following equation system:
Phase1 = Hres*K1
Phase2 = (Hres*K2) + (D*4π/λ)
where Hres is the is the residual height (_height, derived from the interferometric technique); V is the displacement velocity (mm/year); D is the displacement (millimeters); K1 and K2 are height-to-phase conversion factors; T1 is the 1st pair acquisition time distance; T2 is the 2nd pair acquisition time distance.
The process is typically executed in two consecutive iterations:
1.The flag "From SLC to Phase Unwrapping" is checked, while the "Generate Slant Range Products" and "Generate Geocoded Products" are not checked. Only the coherence images, flattened/filtered interferograms and unwrapped phase images are generated (in slant range geometry). The "Geometry GCP file", if entered, is used here for the interferogram flattening process.
2.The "Orbital GCP file" is entered (this is mandatory), the flag "From SLC to Phase Unwrapping" is unchecked, while the "Generate Slant Range Products" and "Generate Geocoded Products" are checked. All products (respectively in slant range projection and geocoded) are generated. The application of a linear or not-linear ("Step Model" or "No Model") model can be performed by running two times this 2nd iteration.
The Ground Control Points in the "Orbital GCP file", are selected with the same criteria and for the same purpose of the Ground Control Points used in the Refinement and Re-flattening step. Note that the criteria for the GCPs selection must be fulfilled for both interferometric pairs.
However the possibility to execute all processing (iteration 1 + iteration 2) in one step can be considered in case the "Orbital GCP file" is available.
Input Files
Input Reference File 1
File name of the first pair Reference data (_slc). This file is mandatory.
Input Reference File 2
File name of the second pair Reference data (_slc). This file is optional.
Input Secondary File 1
File name of the first pair Secondary data (_slc). This file is mandatory.
Input Secondary File 2
File name of the second pair Secondary data (_slc). This file is mandatory.
Refinement 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 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. It serves to correct the Reference image/s with respect to the Digital Elevation Model (refer to the Technical Note for more details).
DEM/Cartographic System
Digital Elevation Model file
Digital Elevation Model file name. This should be referred to the ellipsoid. In case a list of input files is entered, the DEM must cover the whole imaged area. This file is optional.
Output Projection
In case that the Digital Elevation Model is not used, it is mandatory to define the Cartographic System.
To use the same coordinate system as another dataset, click the Import from Existing Dataset button and select the source dataset.
To apply the same Coordinate System of the current selected layer
The reset icon allows to reset the coordinate system field.
Parameters - Principal Parameters
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.
Product Coherence Threshold
Pixels with coherence values smaller than this threshold will be set to dummy (NaN) in the final - i.e. geocoded - products generation.
From SLC to Phase Unwrapping
By setting this flag, the processing is executed until the phase unwrapping (1st iteration in the technical note).
Generate Slant Range Products
By setting this flag, the slant range output products are generated (2nd iteration in the technical note).
Generate Geocoded Products
By setting this flag, the geocoded output products are generated (2nd iteration in the technical note).
Model Type
The choice is given between the following models:
•Linear, the displacement velocity (mm/year) is calculated;
•Step, the displacement magnitude (in millimeters) is calculated;
•No Model, the displacement magnitude (in millimeters) is calculated.
Refer to the Technical Note for further informations.
Refinement method
The choice is given between the following refinement methods:
•Automatic Refinement;
•Polynomial Refinement;
•Orbital Refinement.
Refer to the flattening section of the Preferences for further information about these methods.
Refinement Residual Phase Polynomial Degree
Degree of the polynomial used to estimate the phase ramp, which will be removed from the input unwrapped phase during the Re-flattening operation. In case this value is higher that the number of input Ground Control Points, it will be automatically decreased. The default values of 3 means that a phase ramp in range and azimuth direction plus a constant phase offset will be corrected. In case only the phase offset correction is needed, the polynomial degree will be set to 1.
Coregistration With DEM
By setting this flag, the output will be coregistered with the Digital Elevation Model.
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 Phase Unwrapping, Technical Notes for further information.
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:
•Adaptive window;
•Boxcar window;
•Goldstein.
Refer to the Preferences description for further information about these methods.
Coherence from Fint
By setting this flag, the coherence is computed using the filtered interferogram (_fint) instead of the unfiltered one (_dint).
X Dimension (m)
The grid size in Easting (X) of the output geocoded data must be defined; the default unit of measure is meters.
Note that - for the Geographic projection - if values higher than 0.2 are entered they will be considered as metric units and then automatically, and roughly, converted from meters to degrees; if values lower than 0.2 are entered they will be considered as degree and used as such without any conversion.
Y Dimension (m)
The grid size in Northing (Y) of the output geocoded data must be defined; the default unit of measure is meters.
Note that - for the Geographic projection - if values higher than 0.2 are entered they will be considered as metric units and then automatically, and roughly, converted from meters to degrees; if values lower than 0.2 are entered they will be considered as degree and used as such without any conversion.
Mean Window Size
The mean filtering, of the interferometric height output products - i.e. geocoded -, is carried out. The window filter size must be specified. If zero is entered, the mean filtering is not applied.
Interpolation Window Size
The dummy values, in the interferometric height and displacement output products - i.e. geocoded -, are interpolated. The interpolated value is the average of the valid values in a window of the size specified. If zero is entered, the interpolation is not applied
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 - Geocoding
It brings to the geocoding 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 phase unwrapping parameters 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 - Refinement
It brings to the flattening 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 Root Name
Name of the output root. This file is mandatory.
_cc
Slant range coherence with the associated header files (.sml, .hdr).
_disp
Slant range displacement map with the associated header files (.sml, .hdr).
_fint
Slant range flattened/filtered interferogram with the associated header files (.sml, .hdr).
_height
Slant range residual elevation with the associated header files (.sml, .hdr).
_srdem
Precise Digital Elevation Model (input DEM + InSAR residual height), in slant range geometry, with the associated header files (.sml, .hdr).
_upha
Unwrapped phase with the associated header files (.sml, .hdr).
_vel
Slant range displacement velocity map with the associated header files (.sml, .hdr).
_dem
Precise Digital Elevation Model (input DEM + InSAR residual height), with the associated header files (.sml, .hdr).
_disp_geo
Geocoded displacement map with the associated header files (.sml, .hdr).
_vel_geo
Geocoded displacement velocity map with the associated header files (.sml, .hdr).
In order to distinguish the input SAR pair where each output product comes from, a prefix containing the Reference-Secondary acquisition dates (i.e. yyyymmdd) will be added to the file extensions here above.
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)
| Looks |
The most appropriate range and azimuth multi-looking factors are calculated.
References
Consult the reference guide specific to each processing step.