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<< Click to Display Table of Contents >> Interferometry - Interferometric Tools - Digital Elevation Model / Ellipsoidal Flattening |
  
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<< Click to Display Table of Contents >> Interferometry - Interferometric Tools - Digital Elevation Model / Ellipsoidal Flattening |
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Purpose
The constant phase (due to the acquisition geometry) and the phase expected for a flat Earth or for a known topography (in case a Digital Elevation Model is inputted) are separated from the residual - differential - phase.
This functionality can be used also to generate the synthetic phase only from orbital data, system and processing parameters and the Digital Elevation Model (alternatively the ellipsoidal height).
Technical Note
The interferogram is split in two components:
| - | Low frequency phase, which is related to the reference Digital Elevation Model topography (or ellipsoidal height) and to the constant phase (phase variation intrinsic to the InSAR system geometry). This is the synthetic phase (_sint). |
| - | High frequency phase, which is related to the temporal phase variations between Reference and Secondary (e.g. land changes or atmospheric variations) and to the difference with respect to the reference Digital Elevation Model topography (or ellipsoidal height). This is the differential/residual phase or flattened interferogram (_dint). |
If a reference Digital Elevation Model is entered as input the flattening process is executed by removing the available topography. The better the reference Digital Elevation Model accuracy/resolution the better the result in terms of topography removal.
If a reference Digital Elevation Model is not entered as input, then a Reference Height must be provided. In this case the flattening process is executed assuming a ellipsoidal model with constant height.
The DEM flattening is executed by transforming the input Digital Elevation Model into the Reference slant range image geometry. In case of precise orbits and accurately geocoded reference Digital Elevation Model, this process is run in a fully automatic way. However, in case of inaccuracy in the satellite orbits or in the Digital Elevation Model geolocation, a Ground Control Point is required to correct the SAR data (i.e. Reference acquisition of the interferometric pair) with respect to the reference Digital Elevation Model. In this case the shift calculated in the coregistration process is combined with the Ground Control Point shift in order to correct the Secondary data according to the Reference data.1
It is important to note that:
❖In case the "Reference input file" has already been corrected with the manual or the automatic procedure the GCP is not needed.
❖In case the "Reference input file" is correct (i.e. the nominally geocoded image fits with the DEM), while the orbital parameters of the "Secondary input file" are not accurate (i.e. the nominally geocoded image does not fit with the DEM), the GCP is not needed but the flag "Automatic Secondary Orbit Correction", in the Preferences>Flattening, must be checked.
In case the orbits are not accurate, the differential interferogram (_dint) can contain some residual phase (i.e. residual orbital fringes). These fringes can be removed by setting the "REMOVE RESIDUAL PHASE" flag in the Preferences>Flattening, before running the flattening process.
When this functionality is used to make only the synthetic phase, the Reference and Secondary input files must be those coming from the interferogram generation process.
Input Files
Interferogram File
File name of the previously generated interferogram (_int). This file is mandatory if the "Compute Synthetic Phase Only" flag is unchecked.
Input Reference File
File name of the Reference Intensity data (_pwr). This file is mandatory.
Input Secondary File
File name of the Secondary coregistered Intensity data (_pwr). 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.
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
Compute Synthetic Phase Only
By setting this flag only the synthetic phase is generated.
Coregistration with DEM
By setting this flag the data will be coregistered with the optional input Digital Elevation Model.
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 - Coregistration
It brings to the coregistration 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 - 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.
_dint
Flattened interferogram with the associated header files (.sml, .hdr).
orig_
Original phase, before the Residual Phase Frequency Removal, with the associated header files (.sml, .hdr). This file is generated only when the Preferences>Flattening>Remove Residual Phase Frequency flag is checked.
_sint
Synthetic phase with the associated header files (.sml, .hdr).
_srdem
Digital Elevation Model, in slant range geometry, with the associated header files (.sml, .hdr).
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.
Task, SARscapeBatch object, SARscapeBatch script example
References A. Monti Guarnieri, C. Cafforio, P. Guccione, D. Nüesch, D. Small, E. Meier, P. Pasquali, M. Zink, Y. L. Desnos: "Multi-mode ENVISAT ASAR Interferometry: Techniques and Preliminary Results". Proceedings of EUSAR Conference 2002.