ANSI-C programs: dis_ipta.c
NAME
dis_ipta - display regression of phase with respect to time
interval and baseline for selected points
SYNOPSIS
dis_ipta <plist> <pmask> <pSLC_par>
<ppos> <itab> <pbase> <bflag>
<pdiff> <pdiff_type> <ras> [dh_max] [def_min]
[def_max] [model] [bmax] [dtmax] [mag] [win_sz]
| <plist> | (input) point list (int) |
| <pmask> | (input) point data stack of mask values (uchar, set to - to accept all points) |
| <pSLC_par> | (input) stack of SLC/MLI parameters (binary) |
| <ppos> | (input) point data stack of interpolated point target positions (fcomplex, enter - to use plist coordinates) |
| <itab> | (input) table associating interferogram stack records
with pairs of SLC stack records (ascii) (line entries are: pSLC_rec1 pSLC_rec2 itab_rec_num switch_flag) |
| <pbase> | (input) stack of baseline parameters (binary) |
| <bflag> | baseline flag (0:initial baseline 1:precision baseline) |
| <pdiff> | (input) point data stack of differential interferograms (fcomplex or float) |
| <pdiff_type> | type of pdiff (0: float(unwrapped) default=1: fcomplex) |
| <ras> | (input) raster reference image with PT locations marked (SUN *.ras, or BMP *.bmp) |
| [dh_max] | maximum height correction for initial fit (m, enter - for default: 60.) |
| [def_min] | minimum deformation rate difference for initial fit (m/year, enter - for default: 0.005) |
| [def_max] | maximum deformation rate difference for initial fit (m/year, enter - for default: 0.005) |
| [model] | phase regression model: 1: a0 + a1*bperp[i] 2: a0 + a1*bperp[i] + a2*delta_t[i]) (default) 3: a1*bperp[i] 4: a1*bperp[i] + a2*delta_t[i] 5: a0 + a2*delta_t[i] 6: a2*delta_t[i] |
| [bmax] | maximum perp. baseline (m) considered, (-1 = all records, default=-1) |
| [dtmax] | maximum time interval (days) considered, (-1 = all records, default=-1) |
| [mag] | zoom magnification factor (default=3) |
| [win_sz] | zoom window size before magnification (default=128) |
EXAMPLE
dis_ipta testsite.plist testsite.pmask testsite.ppar -
testsite.itab testsite.pbase 0 testsite.pdiff 1 testsite.pt.ras
20. -.01 0.005 2
Displays the SUN/BMP rasterfile testsite.pt.ras which shows the point locations, and conducts for the interactively selected pairs of points (one is the reference point) an investigation of the baseline and time dependence of the differential interferometric phase (relative to the phase of the reference point), estimates height corrections, linear deformation rates, and a quality measure for the regression, and displays the phase values together with the regression function.
DESCRIPTION
dis_ipta is a tool for a point-wise investigation of the baseline
and time dependence of the differential interferometric phase
(relative to the phase of the reference point).
Interactively, pairs of points are selected in the displayed SUN/BMP rasterfile testsite.pt.ras which shows the point locations. For the selected pairs of points (one is the reference point) an 2-D linear regression function (linear dependences on the perpendicular baseline and time differences) is determined for the differential interferometric phase (relative to the phase of the reference point). Height corrections, linear deformation rates, and the standard deviation of the phase from the fit as a quality measure for the regression, are calculated. Plots showing the phase values together with the regression function are displayed.
In the regression analysis either a one dimensional (linear dependence on perpendicular baseline component) or two dimensional (linear dependences on perpendicular baseline component and linear deformation rate) linear regression function is used. In this regression analysis it is accounted for that wrapped phases are provided in the case of a complex valued interferogram.
The slopes of the regression functions determined are directly
related to the relative height correction, also called delta
height value, and the linear deformation rate.
The standard deviation from the regression function serves as a
quality measure for the regression function and the derived
parameters. The standard deviation of the phase from the
regression funnction is expressed in radian. As input to dis_ipta
interferometric data in point data format is
required.
The point coordinates are defined in a point list. Optionally, a point data stack of interpolated point target positions can be provided. If not provided, the point coordinates of the point list are used. Furthermore, a mask can be provided to indicate for each point if it shall be considered (mask value 1) or not (mask value 0). The interferometric pairs are defined in the itab, a table associating interferogram stack records with pairs of SLC stack records (ascii). Acquisition times and other SLC parameters are provided in the stack of SLC/MLI parameters (binary) and baseline parameters in the stack of baseline parameters (binary). The differential interferogram is provided in a point data stack. Complex valued or unwrapped differential interferograms can be provided (but the same type for all records). Typically, simulated interferometric phase images were subtracted in the calculation of the stack of differential interferograms. Early on in an IPTA investigation initial simulated phases may contain only the topographic and orbital phase terms calculated from an initial DEM and initial baseline estimates from orbit data. Later on improved height values, precision baselines, atmospheric corrections, linear deformation trends etc. may be considered.
On the command line a number of parameters can be indicated to configure and optimize the regression analysis. These parameters are discussed in the following.
For the interferometric baselines it can be indicated if the initial estimate or the precision estimate shall be used.
In the case of the wrapped phase values the regression analysis is done in two steps. The best regression function among a predefined set of functions is determined. In a second step the least squares analysis is conducted. The predefined regression functions for the first step are derived based on the indicated maximum height correction and maximum deformation rate difference values indicated. Indicating larger values means that more predefined regression functions are tested which will make the process slower. Indicating a too small value may result in failure to resolve the regression for a point with a high height correction or deformation rate value. It has to be kept in mind that the height correction and deformation rates are relative to the reference point. Consequently, the regression analysis is generally more robust for points near the reference point.
The records considered in the regression analysis can be constrained to short perpendicular baselines and short time intervals.
Either one- or two-dimensional linear regression models can be used. A reason for using the one-dimensional regression model might be to make the regression more robust in the case of only few data records or early on in the analysis when the large height corrections are expected.
The slope of the phase to baseline dependence is used to calculate a height correction value. This height correction value is the height correction of the current point under the assumption that the height of the reference point is correct. The height corrections are indicated in meter (m) and are written to the screen. It is important to note that this improvement is done relative to the selected reference point. The accuracy of the height of a specific point depends on the accuracy of the height of the reference point plus the error in the height correction (and not only the second term).
The slope of the phase to time dependence is used to calculate a linear deformation rate. This linear deformation rate is the deformation rate of the current point relative to the reference point. The deformation rates are indicated in meter per year (m/year) and are written to the screen. It is important to note that the linear deformation rate is relative to the reference point and in addition to any deformation model which may already be considered in the calculation of the differential interferogram.
The residual phase, i.e. the difference between the phase
values and the regression model includes terms related to
atmospheric delay, non-linear deformation, baseline errors, and
signal noise.
For each point the standard deviation of the (unwrapped) phases
from the regressin function is calculated and used as measure for
the quality of the regression.
To select point pairs in the display visible after starting dis_ipta, the cursor is moved near the desired points which can then be selected using the right mouse bottons. Doubble clicking is used to select a (new) reference point, single clicking to select a (new) point. Upon the selection the regression analysis is done for the selected pair and the result is displayed.
To automatically conduct the same type of regression analysis for all points of an image is supported by the programs def_mod_pt and multi_def_pt.
SEE ALSO
def_mod_pt, multi_def_pt, dis_ipta, prox_pt,
ipta.h.
© Copyrights for Documentation, Users Guide and Reference Manual by Gamma Remote Sensing, 2006.
UW, CW, TS, last change 21-Nov-2006