ANSI-C program: fspf.c
NAME
fspf - Fast spatial filter for 2D data
SYNOPSIS
fspf <data_in> <data_out> <width>
[type] [r_max] [spf_type] [MLI_par]
| <data_in> | (input) image data |
| <data_out> | (output) spatially filtered image data |
| <width> | number of samples/row |
| [type] | data type (enter - for default) : 0: fcomplex 1: scomplex 2: float (default) |
| [r_max] | maximum radius range samples (enter - for default: 16) |
| [spf_type] | spatial filter type: 0: uniform average (default for fcomplex and scomplex data) 1: triangular weighted average: 1 - (r/r_max) 2: quadratic weighted average: 1 - (r/r_max)**2 3: Gaussian weighted average: exp(-2.*(r**2/r_max**2)) 4: linear least-squares (default for float data) |
| [MLI_par] | MLI or SLC parameter file with the same number of looks as the data that are being filtered |
EXAMPLES
fspf 19990915_19991020.unw 19990915_19991020.unw_spf 2456 0
100 3
Conducts a fast spatial filtering on the unwrapped phase values stored in the 2-D data set 19990915_19991020.unw (float). Pixels within a radius of 100 pixels are taken into account for the the spatial filtering. The data type of the input and output data set is float. The spatial filter type chosen is a quadratic weighted average (1 - (r/r_max)**2).
fspf 20130906_102231_20130906_102101.diff fspf2.diff 5598 0 16 0 20130906_102231u.mli.par
Conducts a fast spatial filtering on the unwrapped phase values stored in the 2-D data set 20130906_102231_20130906_102101.diff (fcomplex). Pixels within a radius of 16 range pixels are taken into account for the the spatial filtering. The sensor type is read from the MLI parameter file that in this case is GPRI data. The spatial filter type chosen is a uniform weight average.
DESCRIPTIONIn the estimation of orbital phase trends and long-wavelength atmospheric path delays spatial filtering with large filter windows is frequently applied in an ISP processing. Using interp_ad or adf such filtering is supported, but in the case of very large windows it is very slow. The main objective of the program fspf is to provide a useful alternative for such filtering which is computationally much more efficient. fspf can be used for both complex valued point interferograms (e.g. diff obtained after subtracting of the simulated topographic phase, or re-wrapped residual phases from a regression analysis) or float data (residual phases, atmospheric path delays).
It is also possible to filter interferograms, both complex and unwrapped phase from the Gamma Portable Radar Interferometer (GPRI) by specifying an MLI_par. The MLI_par parameter file must have the same geometry and number of looks as the interferogram file or other data that are filtered using fspf. The program determines the sensor type from the MLI_par. If the data are from the GPRI, the program resamples the data to a uniform rectangular grid, different from the native polar format of the GPRI data. The data are resampled to a rectangular grid, filtered, and then resampled to the output grid taking into account the variation in azimuth pixel spacing as a function of range that is characteristic of polar scanned GPRI data.
In the case where the MLI_par is specified for SAR data (not GPRI), the ground range pixel spacing is calculated from the incidence angle at the center of the swath. The data are resampled to a uniform grid in ground-range before filtering and then resampled to the original grid after filtering. This is useful for cases where the interferogram pixels are not close to square with respect to azimuth and ground-range in the multi-look image geometry.
SEE ALSO
interp_ad, adf