Gamma DIFF: Reference Manual

diff_ls_unw

NAME
diff_ls_unw - generate differential interferogram using the least squares derived functional relationship between interferograms to scale and subtract one from the other.

SYNOPSIS
diff_ls_unw <int-1> <unw-2> <DIFF_par> <diff_inr> [int_type] [ph_flag]

<int-1>	(input) complex or unwrapped interferogram 1
<unw-2>	(input) unwrapped phase 2 (topographic phase)
<DIFF_par>	(input/output) DIFF processing parameter file
<diff_int>	(output) difference of interferograms (int-1 - scaled(unw-2))
[int_type]	int-1 type: 0=unwrapped phase, 1=complex interferogram (default=0)
[ph_flag]	phase conjugation flag: 0=normal, 1=conjugate phase (default=0)

EXAMPLES
diff_ls_unw i1.unw.reramp i2.unw.reramp i1_i2.diff_par i1_i2.unw.diff 0
diff_ls_unw i1.int i2.unw.reramp i1_i2.diff_par i1_i2.int.diff 1 0

DESCRIPTION
diff_ls_unw reads two unwrapped interferometric phase images, estimating the phase of the first image by a evaluating a quadratic function of the phase in the second interferogram. The estimate is then subtracted from the phase of the first interferogram and stored in the result. The coefficients of the quadratic function are evaluated using a least squares fit in program diff_ls_fit and stored in the DIFF parameter file.

The first interferogram can be either complex valued or real-valued unwrapped phase. In the case where the input is complex valued, the differential interferogram will also be complex valued. The advantage of this is that there will be no unwrapping errors in the result, nor will any areas be excluded. No unwrapping will be required of the result if the phase signature has a magnitude less than PI. The user has the option of conjugating the output phase. This is useful if the interferogram is made in time reversed order, i.e. the reference SLC is acquired after the second SLC used to make the interferogram. In this way all the differential phase shifts have the same relationship with respect to motion towards or away the radar.

It is preferred that the baseline of the second interferogram is sufficiently large. Using the phase of an interferogram with a very short baseline as a reference for the topographic phase usually leads to poor results because of the up-scaling of non-topographic phase components. Be sure to use the same interferograms that were used to estimate the coefficients of the quadratic function and stored in the DIFF parameter file.

diff_ls_unw requires that interferograms have the original phase trend and therefore are not flattened. The program ph_slope_base may be used to add back the phase trend removed when flattening the interferogram using an ellipsoidal Earth model. diff_ls_unw may be used for 2-pass, 3-pass, and 4-pass differential interferometry.