ANSI-C program: pre_rc_RSAT.c
NAME
pre_rc_RSAT - Prefilter and
range compression of Radarsat StripMap mode raw data. Includes
correction of along-track gain variations and implements
secondary range migration.
SYNOPSISpre_rc_RSAT
<SAR_param> <PROC_param> <raw_data>
<rc_data> [prefilt_dec] [loff] [nl] [nr_samp] [kaiser]
[filt_lm] [nr_ext] [fr_ext]
| <SAR_param> | (input) SAR sensor parameter file |
| <PROC_param> | (input) MSP Processing Parameter File |
| <raw_data> | (input) uncompressed raw SAR signal data file |
| <rc_data> | (output) prefiltered range compressed data file |
| [prefilt_dec] | prefilter decimation factor (default from proc_par) |
| [loff] | number of lines offset (enter - for default=parameter file value) |
| [nl] | number of lines filter/range compress (enter - for default=parameter file value) |
| [nr_samp] | number of range samples (enter - for default from PROC_param) |
| [kaiser] | range chirp Kaiser window parameter beta (default=2.120, -25 dB side-lobes) |
| [filt_lm] | filter length multiplier (default filt_lm=8) FIR_length = FIR_lm *prefilt_dec + 1 |
| [nr_ext]; | near range swath extension in samples (default from PROC_par) |
| [fr_ext] | near range swath extension in samples (default from PROC_par) |
EXAMPLE
pre_rc_RSAT RSAT.par
pBogota.slc.par Bogota.raw Bogota.rc
DESCRIPTION
Similar to pre_rc but also includes
secondary range migration and correction of along-track receiver
gain variations. Secondary range migration corrects for range
defocusing that can occur as a result of relatively high-squint
angles. RadarSat data often has Doppler centroids corresponding
to squints of over 3 degrees. This program compensates for
along-track variations in receiver gain as recorded in the sensor
information contained in the raw data. Gain values can change
every 8 echoes along track. This program takes into account that
the echo record length varies along-track due to the inclusion of
rechirp samples in the header
This program has the option to perform decimation in azimuth (prefiltering) by applying a bandpass filter followed by subsampling. This is useful for survey mode processing to generate a "quicklook" image. Any integer decimation factor can be used because. The filter is implemented with as an FIR filter in the time-domain. The number of taps in the finite impulse response filter determines how closely the azimuth filter approximates an ideal response. Since the Doppler centroid varies in the cross-track direction, somewhat better results may be obtained by range compressing the entire data set followed by applying the azimuth bandpass filter and decimation rather than filtering prior to range compression. The program prefilt performs this function on the range compressed data set.
pre_rc_RSAT has the capability to extend the processed image swath beyond the region of full resolution. The nominal number of samples in the range compressed data is the number of echo samples processed minus the number of samples in the range chirp. Outside of the nominal full resolution swath are two bands, one in the near range and the other in the far range. Both of these bands are as wide as the range chirp width in samples. Across these bands the resolution degrades linearly starting at the full resolution and going to zero. These regions also fade in intensity proportional to the loss in resolution due to the decreasing number of echo samples for these image pixels. The user can specify the swath extension for both the near and far range in the processing parameter file or via the command line parameters nr_ext and fr_ext .
SEE ALSO
Users Guide, typedef_MSP.h, Sensor parameter file, MSP Processing Parameter File, prefilt.