Gamma ISP: Reference Manual

SR_to_GRD

NAME
SR_to_GRD - Slant range (SR) to ground range (GRD) image transformation.

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

<SLC_par>	(input) SLC parameter file of input slant range image
<off/int_par>	(input) ISP offset/interferogram parameter file of input image (or - for input image in SLC/MLI geometry)
<GRD_par>	(input/output) SLC parameter file of output ground range image
<in_file>	(input) slant range image (float)
<out_file>	(output) ground 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)
[grd_rsp]	output image ground range sample spacing (m) (default = (input image azimuth spacing) * azlks)
[grd_azsp]	output image azimuth sample spacing (m) (default = (input image azimuth spacing) * azlks)

EXAMPLES

SR_to_GRD 8560.mli.par - 8560.grd.par 8560.mli 8560.mli_grd 1 1 1 20.0 20.0

Converts the multi-look intensity image 8560.mli from slant-range to ground-range with a 20m pixel spacing in ground range and azimuth (using spline interpolation).

SR_to_GRD 8560.slc.par - 8560.grd.par 8560.mli 8560.mli_grd 3 3 2 50.0

Converts the multi-look intensity image 8560.mli from slant-range to ground-range with a 50m pixel spacing in ground range and azimuth. Prior to the geometric transformation a 3 x 3 multi-looking is performed to reduce the spatial resolution of the input image to a resolution similar to that of the output ground-range image. Logarithmic spline interpolation is used.

SR_to_GRD 8560.slc.par 8560_8059.off 8560_8059.grd.par 8560_8059.cc 8560_8059.cc_grd 1 1 1 20.0

Converts the real valued coherence image 8560_8059.cc from slant-range to ground-range with a 20m pixel spacing in range and azimuth. The input geometry is defined by 8560.slc.par and 8560_8059.off.

DESCRIPTION
This program transforms real valued images from slant-range to ground-range geometry. The input and output image data are of type float. Typical examples to be converted are backscatter intensity images (as generated by multi-looking and detection of an SLC or in the interferometric processing) and coherence images. The input image geometry is specified by the SLC parameter file (*.slc.par) and the ISP/offset parameter file (*.off). For a multi-look intensity image generated with the program multi_look, only the SLC parameter file of the MLI image (*.mli.par) is required. In this case - is indicated on the command line instead of the ISP/offset parameter file name. The output geometry is specified in the GRD parameter file (*.grd.par). The format of the SLC parameter file of the ground range (GRD) image which has the same format as the SLC parameter files of SLC and MLI slant range images.

In the case that the indicated SLC parameter file of the ground range image (*.grd.par) is not existing a new output SLC parameter file (*.grd.par) is created. The selected output image near range ground range value corresponds to the near range slant range position of the input image. Either the indicated output ground range and azimuth pixel spacings are used, or if nothing is indicated the output pixel spacings are calculated as the input image azimuth pixel 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 GRD parameter file (*.grd.par) is provided no new GRD parameter file (*.grd.par) is created. Near range ground range, image starting time, ground range and azimuth pixel spacing, number of ground range samples and number of azimuth lines indicated in the provided GRD parameter file 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 ground range geometry defined in the GRD 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 ground range. Then edit the GRD parameter file to select a subsection and then transform only the data for the selcted sub-section.

In the case the SLC parameter file of the output 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. For an ERS 5-look image for example the projected resolution is around 20m x 20m. When resampled to a ground-range image with 20m or 25m pixel spacing multi-looking factors 1 in azimuth and range are appropriate. When resampling the same image to a ground-range image with 100m multi-looking factors 5 in azimuth and range is preferred. This multi-looking is done prior to the geometric tranformation.

If the output image spacing is not specified, then the output image azimuth and ground-range pixel spacing are determined by multiplying the input image azimuth spacing by the number of azimuth looks. The ground range is determined by making a best spherical fit to the earth curvature across track, perpendicular to the heading. The distance from the satellite ground track to the start of the image swath in ground range is stored in the range to start of GRD parameter file *.grd.par file. For nearest-neighbor resampling, two dimensional quadratic spline interpolation, and two-dimensional quadratic spline interpolation the interpretation of the image in terms of logarithmic scale dB values may be selected as an option to prevent generation of negative values in the output image. 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 raster or BMP format image using raspwr.

SEE ALSO
GRD_to_SR, multi_look, dispwr, raspwr.