Help Content > Interferometric Stacking > PS & E-PS > 4

Purpose

This is the final inversion, which uses the first linear model products coming from the previous step to estimate the atmospheric phase components.

The second model inversion is implemented to derive the date by date displacements, after removing the atmospheric phase components and eventually fit the final displacement velocity model. This step is mandatory.

Technical Note

The re-flattened interferograms are used to estimate the displacement related information (i.e. velocity, residual heights and date specific displacements).

Unlike the SBAS tool, just one model is implemented:

•Linear Model, to estimate height and displacement velocity.

The model can be synthesized as follows:

Disp = K + V*(t-t0)

where Disp is the displacement at time t; K is the constant term of order zero, which is used only for the final fitting process; V is the displacement velocity;

Once the date by date displacement measurements (known as high pass components) are carried out, the program performs the estimate of the atmospheric effects.

First, the linear model previously estimated is subtracted date by date, from the interferograms measurements (_dint files). Then the atmospheric correction is performed by the following two filtering procedures:

•Atmosphere Low Pass, this accounts for the spatial distribution of the atmospheric variations. It is implemented by using a square window: large windows are more suitable to correct large scale variations, while small windows are better to correct isolated artifacts due to localized variations. The smaller is the window size, stronger will be the filter effect.

•Atmosphere Hi Pass, this accounts for the temporal distribution of the atmospheric variations. It is implemented by using a temporal window: large windows are more suitable to correct effects with low temporal variability, while small windows are better to correct frequent atmospheric variations. The bigger is the window size, stronger will be the filter effect.

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.

It is worthwhile to mention that the re-flattening, which is performed on the displacement products, does not foresee the orbital refinement; it means than only a ramp (using minimum three GCPs) or a constant term (using minimum one GCP) can be removed..

A graphic, showing the extracted displacement information, can be created using the General Tools>Raster analyzer.

Input Files

Auxiliary file

Reference file generated as output of the "Connection Graph" step and possibly updated afterwards. This file is mandatory.

Parameters - Principal Parameters

Atmosphere Low Pass Size (days)

Enter the window size, in meters, to apply the spatial distribution related filter (refer to the Technical Note).

Atmosphere High Pass Size (m)

Enter the window size, in days, to apply the temporal distribution related filter (refer to the Technical Note).

Rebuild All

By setting this flag the second step of the SBAS Inversion 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.

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 - Cluster

It brings to the cluster 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.

Other Parameters are automatically loaded by reading the work_parameter.sml file updated in the first inversion step (Principal Parameters).

Relax Interpolation

By setting this flag the relax interpolation is carried out. This interpolation is applied only to the atmosphere layers output.

Displacement Sampling (mm/year)

This corresponds to the sampling frequency (in mm/sec) which is used to estimate the displacement velocity.

Min Displacement Velocity (mm/year)

This corresponds to the value expected (in mm/year) as the minimum displacement velocity.

Max Displacement Velocity (mm/year)

This corresponds to the value expected (in mm/year) as the maximum displacement velocity.

Residual Height Sampling (m)

This corresponds to the sampling frequency (in meters) which is used to estimate the residual height.

Min Residual Height (m)

These correspond to the minimum (negative value) residual height, with respect to the reference Digital Elevation Model.

Max Residual Height (m)

These correspond to the maximum (positive value) residual height, with respect to the reference Digital Elevation Model.

Water Mask (db)

Value in dB used as threshold to retrieve a water body mask from the average intensity image. All the points under this threshold will be removed from the output layers. Active if smaller than 0.

MuSigma Mask

Pixels with Mu/Sigma values smaller than this threshold cannot be kept as Persistent Scatterers.

Output Files

second_inversion

Directory containing the following products:

•Height, corresponding to the correction (in meters) with respect to the input Digital Elevation Model, after atmospheric correction.

•precision_height, corresponding to the estimate in meters of the residual height measurement average precision (refer to the Phase to Height conversion for more details).

•Velocity, corresponding to the mean displacement velocity (in mm/year, after atmospheric correction.

•precision_vel, corresponding to the estimate in millimeter/year of the velocity measurement average precision (refer to the Phase to Displacement conversion for more details).

•cc, corresponding to the multitemporal coherence. It shows how much the displacement trend fits with the selected model.

Meta files allowing to load the specific processing results (_meta).

•slant_atm_meta, which refers to date by date atmospheric related components in slant range geometry. This meta file can be found in the working folder.

•slant_dint_reflat_meta, which refers to the date by date flattened interferograms, measured in slant range geometry, after the atmospheric correction.

•slant_disp_meta, which refers to the date by date displacements, measured in slant range geometry, after the atmospheric correction.

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.

Interferometric Stacking - Persistent Scatterers - 4 - Inversion: Second Step

Interferometric Stacking - Persistent Scatterers - 4 - Inversion: Second Step