ANSI-C programs: prefilt.c
NAME
prefilt - Prefilter and
decimate range compressed SAR data
SYNOPSISprefilt <SAR_param>
<PROC_param> <rc_data> <pre_data> [prefilt_dec]
[filt_lm]
| <SAR_param> | SAR sensor parameter file |
| <PROC_param> | MSP Processing Parameter File |
| <rc_data> | input range compressed data file |
| <pre_data> | prefiltered/decimated range compressed data |
| [prefilt_dec] | prefilter decimation factor (default from PROC_param) |
| [filt_lm] | filter length multiplier (default FIR_lm=8) FIR_length = FIR_lm *prefilt_dec + 1 |
EXAMPLE
prefilt ERS1_ESA.par
p8560.slc.par 8560.rc 8560.prc
DESCRIPTION
prefilt is used to
filter and decimate range compressed data. This may be done to
obtain a survey image product suitable for quicklook images or
interferograms. Survey processing of a scene after range
compression where the range compressed data are decimated by a
factor of 5 to 10 acheives roughly square output samples on the
ground after detection and multi-looking for ERS-1. Calculation
of the azimuth filter coefficients requires knowledge of the
Doppler centroid for each slant range. The filter coefficients
are determined based on the desired decimation factor of the raw
data, and the range dependent Doppler centroid. If a decimation
factor of N is chosen, then the bandwidth of the filter is
1/N*pulse repetition frequency of the radar (PRF). Since the
prefilter/decimation occurs after range compression, large
variations in the Doppler centroid accross the swath do not cause
difficulties. This program may also be used to generate images
from different segments of the azimuth spectrum to measure
angular coherence between SAR image looks.
OPTIONS:
Do not use this program if the data have already been decimated
by one of the range compression programs pre_rc.c, pre_rc_JERS.c, and pre_rc_RSAT.c
SEE ALSO
Users Guide, typedef_MSP.h, MSP Processing Parameter File, pre_rc.c, pre_rc_JERS.c, pre_rc_RSAT.c