ANSI-C program: intf_pt.c
NAME
intf_pt - generate
interferogram from SLC point data stack (single record or all
records)
SYNOPSIS
intf_pt <plist> <pmask> <itab>
<rec_num> <pSLC> <pint> <type>
[pSLC_par]
| <plist> | (input) point list (int) |
| <pmask> | (input) point data stack of mask values (uchar, set to - to accept all points) |
| <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) |
| <rec_num> | record number to process (default -: all records) |
| <pSLC> | (input) point data stack of interpolated SLC values (fcomplex or scomplex) |
| <pint> | (output) point data stack of interferograms (fcomplex) |
| <type> | pSLC data type (0:fcomplex 1:scomplex) |
| [pSLC_par] | (input) stack of SLC/MLI parameters used for phase
correction of ENVISAT/ERS interferograms (binary) NOTE: if SLCs have different carrier frequencies, pSLC_par data are required as input |
EXAMPLE
intf_pt plist pmask itab
3 pSLC pint 1
Generates interferogram in point data format for record number 3 of testsite.itab. The mask testsite.pmask is considered concerning the validity of the points.
intf_pt plist - itab - pSLC pint 1
Generates interferograms in point data format for all records of itab. No mask is provided, all points of the point list are considered.
INSTALLATION
Source code intf_pt.c in ./IPTA/src, executable version intf_pt
in ./IPTA/bin
DESCRIPTION
intf_pt generates
interferograms (in point data format) from SLC data in an SLC
point data stack. This can be done for a single record or for all
records. The coordinates of the points considered are defined in
the point list. The optional mask file indicates for each point
if it is valid (1, i.e. considered) or not volid (0,
excluded).
The itab is a text file which associates the interferogram stack records with pairs of SLC stack records. For each interferogram stack record the itab contains a line with the SLC stack record number of the reference SLC, the SLC stack record number of the second SLC in the interferometric pair, the line number in the itab file used only for reference, and a flag (1 or 0) to switch a record on or off (i.e. to consider or exclude a record when processing all records).
The input SLC data are provided in a point data stack containing the registered SLC data can either fcomplex or scomplex type. The normalized complex-valued interferogram is calculated for each valid point of the point list. Valid points are points with non-zero SLC values and a non-zero mask value (if provided). The calculated interferogram values are "single-look", consequently the magnitude is 1.0 (and does not correspond to a degree of coherence). The argument of the complex number is the wrapped interferometric phase. The type of the point data stack of complex-valued interferograms is fcomplex.
In the "single-look" case the normalized complex valued
interferogram is defined by:
complex interferogram = (s1s2*)/sqrt((s1s1*)(s2s2*)).
s1 and s2 are the single look complex values of SLC-1 and SLC-2,
* stands for conjugate complex, i.e, (a+jb)* = (a-jb).
If a new output stack name is indicated the stack is created. Indicating a record number larger than the highest record number of the indicated stack results in an increase of the stack size. No common-band filtering of the range or azimuth spectra is applied in the interferogram calculation. For point targets such filtering is not required.
To display the complex valued interferograms contained in the point data stack the programs pt2data or pt2d can be used to convert the point data to raster data format which can then be displayed using conventional display programs. Alternately, the program ras_data_pt can be used to generate the raster images directly.
In the case where some of the SLC data have differing center frequencies, for example with a mixed ERS, ASAR, stack, the the SLC parameter stack pSLC_par must be supplied on the command line. An additional phase compensation term is calculated and applied to ERS-ASAR cross-platform point interferogram data. The compensation phase pc is given by
pc = (k2 -k1) * r1
Where where k1, k2 are the wave numbers -4*PI fc/C of SLC-1 and SLC-2 respectively, and r1 is the slant range in SLC-1.
OPTIONS
none.
SEE ALSO
ras_data_pt, pt2data, pt2d, ipta.h.