SARGEO

Description

SARGEO registers a SAR image to a simulated image created by SARSIM1 using a set of GCPs tying the actual SAR image to the simulated SAR image.

Parameters

Name	Type	Length	Value range
Input: Input raster channel *	Raster port	1 - 1
InputElevation: Input elevation channel *	Raster port	1 - 1
Output: Output corrected SAR image channel *	Raster port	1 - 1
InputGCP: Input GCP segment *	GCP port	1 - 1
InputText: SAR modeling text segment *	Text port	1 - 1
Resampling Method	String	0 - 1	NEAR \| BILIN \| CUBIC \| SHARP Default: NEAR
Working Memory Size	Integer	0 - 1	1 - 2048 Default: 16

* Required parameter

Parameter descriptions

Input: Input raster channel

Specifies the input image channel that contains the actual SAR image to rectify. The input channel must contain integer values between 0 and 32767. Integer values greater than 32767 are translated to 32767, and real values are truncated to integer values.

InputElevation: Input elevation channel

Specifies the input channel that contains the elevation data used to rectify the input SAR image.

Elevation data can be of any type (including 32-bit real).

The elevation data must be georeferenced in one of the conformal projections listed in the Details section.

Output: Output corrected SAR image channel

Specifies the output image channel to receive the corrected SAR image.

InputGCP: Input GCP segment

Specifies the input GCP segment that contains tie points on the actual image (input file) to the simulated image (created by SARSIM1).

InputText: SAR modeling text segment

Specifies the text segment created by SARSIM1 that contains various radar parameters such as look angles, sensor height, and heading. SARGEO uses this information to generate a sensor model used in the correction process.

The SAR modeling text segment must be contained in the same file that contains the elevation data (either FILO or FILEDEM).

The contents of this segment may be examined, dumped to disk, or read using TEXREP, TEXWRIT and TEXREAD.

Resampling Method

Specifies the resampling mode to use for the output.

Supported values are:

NEAR: Nearest Neighbor resampling. This is the fastest option, and the default value.
BILIN: Bilinear interpolation
CUBIC: Cubic convolution

Note: A fourth resampling option, SHARP, is also available. This method is based on a bilinear interpolation combined with a directional sharpening filter. The SHARP resampling method generates a more visually appealing "sharper" image, but is less accurate radiometrically (see Guindon in the References section).

Working Memory Size

Specifies the amount, in megabytes, of internal memory allocated to SARGEO. The default is 16 MB; a typical amount of memory to allocate is approximately half of the RAM available on the system.

Details

SARGEO creates a geocoded SAR image, given an uncorrected SAR image, a simulated SAR image (created by SARSIM1), a set of ground control points (GCPs) that tie the uncorrected image to the simulated image, and an elevation image previously registered to a conformal projection.

Four basic steps are required to geocode a satellite SAR image to a UTM or other grid:

Georeference the elevation image to a conformal projection.
Run SARSIM1 to create a simulated SAR image in an azimuth-range projection, given the elevation image.
Collect GCPs that tie the uncorrected SAR image to the simulated SAR image.
Run SARGEO to geocode the uncorrected SAR image, given previously collected GCPs and the elevation image.

The elevation data must be georeferenced in one of the following conformal projections:

LCC
MER
MSC
OM
PS
SG
SOM
SPCS (or SPAF, or SPIF)
TM
UPS
UTM
METRE (assumed to represent a conformal projection)

Georeferencing data is stored in the georeferencing segment (segment 1) of the input file (FILI).

Algorithm

The algorithm used by SARSIM1 is derived from the GENSIM function, which is part of SABOTS (SAR Analysis Based On Terrain Simulation) from Dr. Bert Guindon.

The algorithm used by SARGEO can be found in the following paper:

B. Guindon, M. Adair, 1992. "Analytic Formulation of Spaceborne SAR Image Geocoding and 'Value-Added' Product Generation Procedure Using Digital Elevation Data", Canadian Journal of Remote Sensing, Vol. 18, pp. 2-11.

SARGEO derives a first-order polynomial transformation from the ground control points which tie the uncorrected image to the simulated image. Then, interpolation is used to determine each output pixel value.

References