Gamma MSP: Reference Manual

doppler

ANSI-C programs: doppler.c, doppler_real.c

NAME
doppler,doppler_real - Calculate Doppler centroid as a function of slant range using the echo cross correlation from SAR raw data (IQ ADC format: doppler, offset-video ADC: doppler_real).

SYNOPSIS
doppler <SAR_par> <PROC_par> <signal_data> <doppler> [loff] [nsub] [ambig_flag] [namb] [order] [pltflg]

<SAR_par>	(input) SAR sensor parameter file
<PROC_par>	(input) MSP processing parameter File
<signal_data>	(input) uncompressed SAR raw data (IQ data)
<doppler>	(output) Doppler centroid as function of slant range
[loff]	number of lines offset (enter - for default: PROC_par loff value)
[nsub]	number of azimuth subapertures (enter - for default: 12)
[ambig_flag]	Doppler ambiguity resolution flag 0 = use unambiguous Doppler Ambiguity Resolver (DAR) estimate (default) 1 = estimate Doppler ambiguity number from the Doppler slope 2 = command line entry for the Doppler ambiguity number
[namb]	user defined number of Doppler ambiguities to add to the Doppler function (enter - for default: 0)
[order]	order of polynomial used to fit the range Doppler function 0-->3: (enter - for default: 1)
[pltflg]	Doppler centroid plotting flag: 0: none (default) 1: output plot in PNG format

doppler_real <SAR_param> <PROC_param> <signal_data> <doppler> [loff] [nprf] [nsub]

<SAR_par>	(input) SAR sensor parameter file
<PROC_par>	(input) MSP processing parameter file
<signal_data>	(input) Uncompressed SAR raw data (IQ data)
<doppler>	(output) Doppler centroid as function of slant range
[loff]	number of lines offset (enter - for default=parameter file value)
[nsub]	Number of azimuth sub-apertures (default=12)
[ambig_flag]	Doppler ambiguity resolution flag 0 = use unambiguous Doppler Ambiguity Resolver (DAR) estimate (default) 1 = estimate Doppler ambiguity number from the Doppler slope 2 = command line entry for the Doppler ambiguity number
[namb]	User defined number of Doppler ambiguities to add to the Doppler function

EXAMPLES

doppler raw/ERS2_ESA.par raw/p19990915.slc.par raw/19990915.fix raw/19990915.dop 0 12 0 0 1 1

DESCRIPTION
doppler, doppler_real - The Doppler centroid is calculated from the SAR raw data (IQ data or video offset data) as a function of slant range using the line to line correlation method developed by Soren Madsen. The Doppler ambiguity can either be set to a given value, estimated from the slope of the doppler centroid with respect to range, or determined from the unambiguous doppler estimated by dop_ambig. A fit of the doppler function in range can then be used to estimate the pitch and azimuth angles of the SAR antenna. A polynomial function is derived from the estimated pitch and azimuth angles to obtain a doppler function that processes the data to lie on a plane intersecting the earth surface. The pitch and azimuth angles are stored in the SAR Sensor parameter file used by the MSP. The polynomial coefficients of the doppler in range is stored in the processing parameter file. The order of the polynomial used for the fit in doppler can be specified on the command line and must in the range from 0 (constant) to 3

It is recommended that the unambiguous doppler estimate from dop_ambig be used to resolve the doppler ambiguity. The data segment used for the estimation can be specified by the user by setting the offset in lines relative to the beginning of the file. The auto-focus program af may also be used to resolve the Doppler ambiguity. Each Doppler ambiguity is equivalent to a shift of the Doppler centroid by the pulse repetition frequency (Hz).

Plotting of the Doppler centroid as a function of range is controlled by the pltflg command line parameter. When the pltflg is 1, the plot of doppler centroid as a function of range is stored as an image in PNG format. A sample centroid plot with the linear fit is shown below.

doppler_real currently does not support direct plotting to a file or screen. However the doppler values and the linear fit to the data can be plotted using gnuplot:
echo " plot '19990915.dop' u 2:3 with lines lc 3, '19990915.dop' u 2:4 with lines lc 1" |gnuplot

This generates a screen plot that shows the doppler centroid in Hertz as a function of slant range (km) and the linear fit of the doppler centroid.