Gamma ISP: Reference Manual

GRD_to_SR

NAME
GRD_to_SR - Ground range (GRD) to slant range (SR) image transformation.

SYNOPSIS
GRD_to_SR <GRD_par> <SLC_par> <off/int_par> <in_file> <out_file> [rlks] [azlks] [interp_mode] [grd_rsp] [grd_azsp]

<GRD_par>	(input) SLC parameter file of input ground range image
<SLC_par>	(input/output) SLC parameter file of output slant range image
<off/int_par>	(input/output) ISP offset/interferogram parameter file of output image (or - for output image in SLC/MLI geometry)
<in_file>	(input) ground range image (float)
<out_file>	(output) slant range image (float)
[rlks]	multi-looking in range (prior to resampling, default=1)
[azlks]	multi-looking in azimuth (prior to resampling, default=1)
[interp_mode]	interpolation mode (default=0:nearest neighbor, 1:spline, 2:spline log)
[sr_rsp]	output image slant range sample spacing (m) (default = c/(2*adc_sampling_rate)
[grd_azsp]	output image azimuth sample spacing (m) (default = (input image azimuth spacing) * azlks)

EXAMPLES

GRD_to_SR 8560.grd.par 8560.mli.par - 8560.mli_grd 8560.mli 1 1 1 8.0 20.0 Converts the multi-look intensity image 8560.mli_grd from ground-range to slant-range with a 8m pixel spacing in slant range and 20 m in azimuth (using spline interpolation).

GRD_to_SR 8560.grd.par 8560.slc.par 8560_8059.off 8560.grd 8560.mli 1 1 2 Assuming 8560.slc.par 8560_8059.off are existing GRD_to_SR converts the multi-look intensity image 8560.grd from ground-range to the slant range geometry defined by parameter files 8560.slc.par and 8560_8059.off. Logarithmic spline interpolation is used.

DESCRIPTION
This program resamples real valued images from ground-range to slant-range. The input and output image data are of type float. Typical examples to be converted are PRI products or images (backscatter, coherence, etc.) previously transformed to ground-range geometry using GRD_to_SR. The input image geometry is specified by the SLC parameter file of the ground range image (*.grd.par). For a multi-look intensity image generated with the program multi_look only the SLC/MLI parameter file is required. In this case - is indicated on the command line instead of the ISP/offset parameter file name.

The output image geometry is specified by the SLC parameter file (*.slc.par) and the ISP/offset parameter file (*.off). If a new parameter file is created for the output image no ISP/offset parameter file (*.off) is required. In this case - is indicated on the command line instead of the ISP/offset parameter file name.

In the case that the indicated SLC parameter file (*.slc.par or *.mli.par) of the output slant range image is not existing a new MLI parameter file (*.mli.par) is created. The selected output image near range slant range value corresponds to the near range ground range position of the input image. Either the indicated output slant range and azimuth pixel spacings are used, or if nothing is indicated the output pixel spacings are calculated as sr_rsp = c/(2*adc_sampling_rate) with c the speed of light and the output image azimuth pixel spacing equal to the input image azimuth spacing multiplied with the indicated azimuth multi-looking factor. The output image starting time corresponds to the input image starting time. Offsets indicated in the *.off file are accounted for. The ouput image geometric parameters are determined such that the ouput image covers the entire input image.

In the case an already existing SLC parameter file for an output MLI image (*.mli.par) or that existing SLC parameter file and an existing ISP/offset parameter file are provided no new parameter files for the output slant range geometry are created. Near range slant range, image starting time, slant range and azimuth pixel spacing, number of slant range samples and number of azimuth lines indicated in the provided parameter files are used (without consideration of sample spacing values indicated on the command line). This concept allows to transform only the sub-section of the input image which corresponds to the output slant range geometry defined in the MLI parameter file. To define such a sub-section the output parameter file needs to be edited. You may, for example first transform the entire image to slant range. Then edit the MLI parameter file to select a subsection and then transform only the data for the selcted sub-section. This concept is particularly useful when transforming back data from ground to slant range which was previously transformed from slant ro ground range with the program GRD_to_SR.

In the case the SLC parameter file of the input ground range image contains slant range polynomial coefficients (as provided for ENVISAT ASAR ground range images) this polynomial is used for the transformation, otherwise the slant range to ground range conversion is calculated asuming a local spherical earth model.

The number of looks selected in range and azimuth should roughly correspond to the desired image spacing to achieve the best radiometric and geometric fidelity. The ground range is determined by making a best spherical fit to the earth curvature across track, perpendicular to the heading. In the case no slant range polynomials are provided the distance from the satellite ground track to the start of the image swath in ground range is stored as the near range in the parameter file. OIn the case a polynomial is provided this near range is usually equal to 0.0, unless a sub-section of the ground range image was selected.

For the resampling nearest neighbor, two dimensional quadratic spline interpolation and two dimensional quadratic spline interpolation of the input image in logarithmic scale (dB values) can be selected. The real valued input and output image data may be displayed using dispwr, Notice that the image width changed during the transformation. Alternately, the intensity image can be scaled and stored as a SUN rasterfile image using raspwr.

SEE ALSO
multi_look, dispwr, raspwr.