<< Click to Display Table of Contents >> Navigation:  Help Content > ScanSAR Interferometry Module > Reference Guide > ScanSAR Interferometry Module - 5B - Phase to Displacement Conversion and Geocoding

Purpose

 

The absolute calibrated and unwrapped phase values are converted to displacement and directly geocoded into a map projection. This step is performed in a similar way as in the geocoding procedure (Basic module), by considering the Range-Doppler approach and the related geodetic and cartographic transforms. The fundamental difference with the geocoding step is that the Range-Doppler equations are applied simultaneously to the two antennae, making it possible to obtain not only the displacement of each pixel, but also its location (Easting, Northing) in a given cartographic and geodetic reference system.

 

As result of this step also the coherence image is geocoded.

 

Technical Note

 

Each 2π cycle ( interferometric fringe) of differential phase corresponds to half wavelength of displacement along the Slant Range direction (SAR viewing direction). It is possible to specify any vector (i.e direction and inclination) where the measured slant range displacement - component of the deformation in the satellite viewing direction - will be projected. Hence this vector represents the re-projection of the slant range deformation component onto a direction on the ground which is known a-priori and specified by the user (i.e. "vertical" in case of subsidence; "slope" in case of landslides; "custom" in any other case).

 

The output map shows displacement magnitude in meters:

 

Displacement Custom Direction

Direction and inclination of the displacement vector can be specified. As an example an "azimuth angle" of 45° means that the displacement is oriented North 45° East and the movement is expected Northeastward; while an "azimuth angle" of 225° means that the displacement is always oriented North 45° East, but the movement is expected Southwestward. Positive inclination angles indicate upward movement; negative inclination angles indicate downward movement.

 

Precision

This output product, which is derived from parameters such as coherence and wavelength, provides an estimate (i.e. standard deviation value) of the measurement precision. The higher this value the lower the measurement precision. The formula used for the precision calculation is:

 

where γ is the interferometric coherence.

 

It is important to outline that the Refinement and Re-flattening step must have been performed previously.

 

Input Files

 

Coherence file

File name of the coherence (_cc). This file is optional.

 

Unwrapped Phase file

File name of the reflattened unwrapped phase (_upha). This file is mandatory.

 

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

 

Product Coherence Threshold

Pixels with coherence values smaller than this threshold will be set to dummy (NaN) in the final products.

 

Vertical Displacement

By setting this flag the map showing the displacement values projected on the vertical direction is generated among the output products.

 

Slope Displacement

By setting this flag the map showing the displacement values projected along the maximum slope is generated among the output products.

 

Displacement Custom Direction

By setting this flag any vector can be specified, in terms of azimuth (Azimuth Angle, measured in degrees from the North - clockwise direction) and inclination (Inclination Angle, measured in degrees from the horizontal plane). The map showing the displacement values projected on the specified direction is generated among the output products.

 

X Dimension (m)

The grid size of the output data in Easting (X)  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 of the output data in Northing (Y)  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.

 

Interpolation Window Size

By setting this flag the dummy values in the output file are interpolated. The interpolated value is the average of the valid values in a window of the size selected.

 

Dummy Removal

By setting this flag the output geocoded files will be automatically resized in order to remove the dummy area exceeding the frame border.

 

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 - Displacement Projection

 

Generate ALOS-ILOS

by setting this flag ALOS and ILOS images from an Interferometric Processing are generated.

 

Vertical Displacement

By setting this flag the map showing the displacement values projected on the vertical direction is generated among the output products.

 

Slope Displacement

By setting this flag the map showing the displacement values projected along the maximum slope is generated among the output products.

 

Displacement Custom Direction

By setting this flag any vector can be specified, in terms of azimuth (Azimuth Angle, measured in degrees from the North - clockwise direction) and inclination (Inclination Angle, measured in degrees from the horizontal plane). The map showing the displacement values projected on the specified direction is generated among the output products.

 

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. It is mandatory.

 

_dem

Input Digital Elevation Model resampled onto the specified cartographic system and grid size, with the associated header files (.sml, .hdr). Its areal extent is the same as the output SAR products.

 

_cc_geo

Geocoded coherence with the associated header files (.sml, .hdr).

 

_ADF

Maximum slope direction values, with the associated header files (.sml, .hdr).

 

_IDF

Maximum slope inclination values, with the associated header files (.sml, .hdr).

 

_SD

Displacement values along the maximum slope direction, with the associated header files (.sml, .hdr).

 

_UD

Displacement values in the direction specified as azimuth and inclination degrees (i.e. custom direction), with the associated header files (.sml, .hdr).

 

_VD

Vertical displacement values, with the associated header files (.sml, .hdr).

 

_disp

Slant Range (satellite view direction) displacement values, with the associated header files (.sml, .hdr).

 

_precision

Estimate of the data quality with the associated header files (.sml, .hdr). This file is generated only if the coherence file is entered as input.

 

_ALOS

Azimuth Line of Sight with the associated header files (.sml, .hdr). Positive angles are measured clockwise from the North; negative angles are measured counterclockwise from the North.

 

_ILOS

Incidence angle of the Line of Sight with the associated header files (.sml, .hdr). The angle is measured between the Line Of Sight and the vertical on the ellipsoid (flat earth).

 

Please Note: the annotations of the geocoded files are displayed in ENVI View according to Preferences Common.

 

 

Note: some outputs are created only if the respective flag is checked. 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.

 

References

 

None.