Help Content > Interferometry Module > MAI Processing

Purpose

This step is crucial for a correct transformation of the unwrapped phase and the Multi Aperture Interferometry (MAI) unwrapped phase information into displacement values. It allows both to refine the orbits (i.e. correcting possible inaccuracies) and to calculate the phase offset (i.e. getting the absolute phase values), or remove possible phase ramps. The MAI unwrapped phase reflattening will be performed by phase ramps removal only.

The execution of this step is mandatory for Displacement Mapping in range and azimuth direction.

To execute this step a Ground Control Point file must be previously created.

Technical Note

Depending on the specific processing parameter setting (Preferences>Flattening>Refinement and Re-flattening/Refinement Method), the polynomials and the correction factors are calculated and written in the header file of the unwrapped phase image (_upha/MAI_upha.sml>interferometric_processing section) - as well as on a popup window when the process is not executed in batch mode - at the process completion; these correction factors/polynomials are:

-	ORShiftOrbitInX - Orbital shift in X direction (in meters) - It is generated if the "Orbital" method is applied.

-	ORShiftOrbitInY - Orbital shift in Y direction (in meters) - It is generated if the "Orbital" method is applied.

-	ORShiftOrbitInZ - Orbital shift in Z direction (in meters) - It is generated if the "Orbital" method is applied.

-	ORAzShiftOrbitInX - Dependency of the shift in X direction, from the azimuth position (in meters per pixel) - It is generated if the "Orbital" method is applied.

-	ORAzShiftOrbitInY - Dependency of the shift in Y direction, from the azimuth position (in meters per pixel) - It is generated if the "Orbital" method is applied.

-	ORAzShiftOrbitInZ - Dependency of the shift in Z direction, from the azimuth position (in meters per pixel) - It is generated if the "Orbital" method is applied.

-	ORPhaseOffset - Absolute phase offset (in radians) - It is generated if the "Orbital" method is applied.

-	ORRMSError - Root mean square error calculated as the difference between the height value of the Ground Control Points and the corresponding value in the interferometric phase (in meters) - It is generated if the "Orbital" method is applied.

-	PhaseError - A-priori achievable root mean square error, calculated as average on the input GCPs (height in meters) - It is generated if the "Default" method flag is checked.

-	RPPPhasePolyDegree - Degree of the polynomial used to estimate the phase ramp - It is generated if the "Polynomial Refinement" method is applied.

-	RPPPhasePoly - The polynomial used to estimate the phase ramp - It is generated if the "Polynomial Refinement" method is applied.

-	RPPRMSE - Root mean square error calculated as the difference between the height value of the Ground Control Points and the corresponding value in the interferometric phase (in meters) - It is generated if the "Polynomial Refinement" method is applied.

The popup window additionally provides, for each input Ground Control Point, the following values:

-	Mean difference between SRDEM - slant range input DEM - and SAR DEM (in meters).

-	Mean difference between Unwrapped Phase and calculated Phase Ramp (in radians)

-	Standard Deviation between SRDEM and SAR DEM (meters).

Very large "ORRMSError" or "RPPRMSE" - root mean square errors - (in the order of hundreds or thousands) eventually bring to wrong results. Care must be paid also when very small "ORRMSError" values (less than 1) are reported; as a rule of thumb errors from some units to some tens are a good preliminary indication that the Ground Control Points have been properly located.

Large "ORRMSError" values can be reported when processing pairs with very small baseline (i.e. less than about 10 meters).

Ground Control Points located on null/dummy value pixels (NaN) are discarded.

The correction parameters are calculated depending on the specific "Refinement Setting" and they are applied to rebuild the following input files:

-	Unwrapped Phase (_upha).

-	MAI unwrapped Phase (_MAI_upha).

-	Flattened Interferogram (_dint or _fint).

-	MAI flattened Interferogram (_mai_fint).

-	Synthetic Phase (_sint).

The points ("Refinement Ground Control Point file") used to calculate the correction parameters (Refinement Setting), shall be selected on the input flattened interferogram (_dint, _fint) in order to avoid areas where topographic fringes remained "unflattened" and "moving areas". The Ground Control Points must be well distributed throughout the entire scene.

An indication about the Ground Control Points quality can be obtained by inspecting the "_refinement.shp" (see "Output" product description below).

If the Interferogram Flattening has been performed using a reference Digital Elevation Model, it is not necessary to specify the co-ordinates of each Ground Control Point; in this case the cartographic co-ordinates (easting, northing and height on the reference DEM) of each GCP are written in the log file at the end of this processing step.

Areas with good coherence should be preferred for the Ground Control Points location. In any case the importance of each GCP is weighted by the program on the basis of its coherence value.

If errors exist in the unwrapped phase image, they must be corrected before running this step. Otherwise wrongly unwrapped areas (disconnected phase "islands") have to be discarded for the Ground Control Points location.

Input Files

MAI Coherence file

Name of the MAI coherence image (_mai_cc). This file is mandatory.

Coherence file

Name of the coherence image (_cc). This file is mandatory.

Input Reference File

File name of the multi-looked Reference Intensity data (_pwr). This file is mandatory.

Input Secondary File

File name of the multi-looked coregistered Secondary Intensity data (_pwr). This file is mandatory.

MAI Unwrapped Phase file

Name of the MAI unwrapped phase (_mai_upha). This file is mandatory.

Unwrapped Phase file

Name of the unwrapped phase (_upha). This file is mandatory.

Synthetic Phase file

Name of the synthetic phase (_sint). This file is mandatory.

Slant Range Digital Elevation Model file

Name of the Digital Elevation Model in slant range geometry (_srdem).

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 if a "Refinement Method" is selected.

Optional Files

MAI Interferogram file

Name of the MAI flattened phase (_mai_fint). This file is optional.

Interferogram file

Name of the flattened phase (_fint). This file is optional.

DEM/Cartographic System

Digital Elevation Model file

Name of the Digital Elevation Model file (geocoded reference DEM). This file is mandatory if it had been used as input for the flattened interferogram generation. If the Digital Elevation Model is omitted, an ellipsoidal height including the cartographic reference system must be set.

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

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

This parameter can not be defined by the user.

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 - Flattening

It brings to the flattening 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 optional.

_reflat_dint/fint

Re-flattened interferogram with the associated header files (.sml, .hdr).

_reflat_mai_fint

Re-flattened interferogram with the associated header files (.sml, .hdr).

_reflat_sint

Re-flattened synthetic phase with the associated header files (.sml, .hdr). This file is generated only if a "Refinement Method" was selected.

_reflat_upha

Re-flattened unwrapped phase with the associated header files (.sml, .hdr).

_reflat_mai_upha

Re-flattened unwrapped phase with the associated header files (.sml, .hdr).

_reflat_srdem

Digital Elevation Model, in slant range geometry, with the associated header files (.sml, .hdr). This file is generated only if a "Refinement Method" was selected.

_reflat.txt

Text file with the orbital correction parameters resulting from the refinement.

_refinement.shp

Shape file containing those points retained (valid GCPs) form the input "Refinement GCP file". The following information is provided if the "Orbital" method is applied:

-	Height value (in meters) from the input DEM in slant range - "ReadHeight".

-	Absolute - "AbsHgtDiff" - and relative - "HeightDiff" - difference (in meters) between the real height (input DEM in slant range) and the height value derived from the corrected orbits.

-	Standard deviation (in meters) of the input "Refinement GCP file" - "SigmaMt" - It is based on interferometric coherence and orbital configuration.

-	Standard deviation (in radians) of the input "Refinement GCP file" - "SigmaRad" - It is based on the interferometric coherence.

The following information is provided if the "Residual Phase" method is applied.

-	Unwrapped phase value (in radians) - "ReadPhase".

-	Absolute - "AbsPhDiff" - and relative - "PhaseDiff" - difference (in radians) between the real phase and its fitted value based on GCPs.

-	Standard deviation (in meters) of the input "Refinement GCP file" - "SigmaMt" - It is based on interferometric coherence and orbital configuration.

-	Standard deviation (in radians) of the input "Refinement GCP file" - "SigmaRad" - It is based on the interferometric coherence.

_refinement_geo.shp

Shape file containing the geocoded location of the valid GCPs used in the refinement process.

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.

The window will be closed.

Help

Specific help document section.

Specific Function(s)

None.

Interferometry - MAI - MAI Refinement and Re-flattening

Interferometry - MAI - MAI Refinement and Re-flattening