Gamma DIFF: Reference Manual

diff_ls_fit

NAME
diff_ls_fit - quadratic least squares functional fit of the relationship between unwrapped interferograms for differential interferometry.

SYNOPSIS
diff_ls_fit <unw-1> <unw-2> <DIFF_par> [nr] [naz] [overlay] [plot_data]

<unw-1>	(input) unwrapped phase 1
<unw-2>	(input) unwrapped phase 2 (topographic phase)
<DIFF_par>	(input/output) DIFF processing parameter file
[nr]	(input) number of range samples for LS fit (default=32)
[naz]	(input) number of azimuth samples for LS fit (default=32)
[overlay]	SUN raster/BMP format overlay file, regions flagged with 0 are excluded ( - for no overlay file)
[plot_data]	(output) data for plotting results LS fit results

EXAMPLE
diff_ls_fit i1.unw.reramp i2.unw.reramp i1_i2.diff_par 32 32 i1.unw.ovr.ras i1_i2.diff_ls_fit

INSTALLATION
Source code diff_ls_fit.c in ./DIFF/src, executable version diff_ls_fit in ./DIFF/bin

DESCRIPTION
diff_ls_fit reads two unwrapped interferometric phase images and determines the phase scaling factors for differential interferometry based on a least squares error (LS) approach. It is preferred that the baseline of the second interferogram is significantly larger than the first interferogram generated from the pair with the known motion. the reason for this is that the phase of the second interferogram is scaled down, thereby reducing atmospheric phase distortions. The opposite situation given a short baseline for the second interferogram causes the phase distortion an noise to be scaled up, leading to poor results.

diff_ls_fit requires that both unwrapped phase images are in original geometry, i.e. not flat-Earth-phase-trend removed. This is necessary to correctly determine the phase scaling factors. To reramp an elliopsoidal Earth-phase-trend removed unwrapped phase image the ISP program ph_slope_base is used. The scaling factors determined by diff_ls_fit are written to the DIFF parameter file. The actual subtraction of the scaled unwrapped phase image 2 is then conducted using diff_ls_unw.

The user can specify an overlay file in Sun raster format to prevent data values to be selected from specific regions. An image of the scene (i.e. the unwrapped phase) in slant range coordinates can be edited using the program xv to create the overlay. Select black (value = 0) as the region fill color in xv and then select rectangles that cover the regions to exclude selection of unwrapped phase data. The edited image must be saved and entered as an optional argument to extract_gcp.

diff_ls_fit may be used for 2-pass, 3-pass, and 4-pass differential interferometry. The data written to an ASCII file allows to generate a plot of the LS fit. Plotting the data can be done with the xmgrace program (xmgrace -nxy plot_data) if the parameter (nr < 16).

SEE ALSO
diff_ls_unw, typedef_ISP.h, typedef_DIFF.h.