SARSIM2

Description

SARSIM2 creates a pseudo-geocoded simulated SAR image with shadow and overlay masks, registered to an elevation raster in a conformal projection.

Parameters

Name	Type	Length	Value range
InputDEM: DEM raster *	Raster port	1 - 1
Output: Output simulated detected SAR image	Raster port	0 - 1
OutputBitLayover: Layover bitmap layer	Bitmap port	0 - 1
OutputBitShadow: Shadow bitmap layer	Bitmap port	0 - 1
Elevation scale	Float	0 - 1	Default: 1,0
Elevation offset	Float	0 - 1	Default: 1,0
Sensor Altitude *	Float	1 - 1	0 -
Sensor Azimuth	Float	0 - 1	0 - 360 Default: 0
Minimum Look Angle *	Float	1 - 1	0 - 90
Near Range Point on DEM	Float	0 - 2
Oversampling Factor	Integer	0 - 1	3 - 15 Default: 5

* Required parameter

Parameter descriptions

InputDEM: DEM raster

Specifies the image channel from the input file that contains the elevation data from which the simulated image data is created.

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

Output: Output simulated detected SAR image

Optionally specifies the 16-bit unsigned output file to receive the simulated SAR image.

OutputBitLayover: Layover bitmap layer

Specifies the output file to receive the overlay bitmap mask.

OutputBitShadow: Shadow bitmap layer

Specifies the output file to receive the shadow bitmap mask.

Elevation scale

Optionally specifies the scale to apply to the elevation values in the input DEM, to convert values to meters. Each pixel value is multiplied by this number to perform the conversion. By default, no scaling is applied and the DEM is assumed to have heights in meters.

Elevation offset

Optionally specifies the offset to apply to the elevation values before these values are, potentially, multiplied by the elevation scale factor. By default, no offset is applied and the DEM is assumed to have heights in meters.

Sensor Altitude

Specifies the platform altitude, in meters, above sea level for the simulated SAR image.

Sensor Azimuth

Specifies the heading angle (or azimuth), in degrees, clockwise from due North for the simulated SAR image.

The angle is between 0.0 and 360.0 degrees; the default is 0 degrees (North).

Minimum Look Angle

Specifies the minimum range look angle, in degrees.

Near Range Point on DEM

Specifies the georeference coordinates for the first pixel (near range point) of the simulated SAR image.

This parameter does not necessarily have to specify a point on the input elevation image. By default, this value points to the upper-left corner of the elevation image.

For descending images, this value should be the coordinate of the upper-right coordinate of the DEM. For ascending images, this value should be the coordinate of the lower-left coordinate of the DEM.

Oversampling Factor

Optionally specifies the oversampling factor. Greater oversampling factors lead to a better visual effect, but may slow down the execution of SARSIM2. The default is 5.

Details

SARSIM2 creates a pseudo-geocoded simulated SAR radar image and two channel showing layover and shadow areas, registered to an elevation image in a conformal projection.

The resulting simulation incorporates all of the inherent spatial ambiguities and radiometric artifacts associated with layover, thereby allowing for direct simulated-to-real comparisons.

The user must specify basic satellite parameters, such as the sensor azimuth angle in degrees clockwise from due North, the altitude above sea level in meters, the SAR minimum look angle, and an arbitrary point for the near range point (first pixel) for the simulated image, specified in georeference coordinates.

The oversampling factor is dependent on the relative sampling intervals of the DEM and the simulated image, the viewing geometry, and the steepest slopes in the region of interest. The default oversampling factor value is 5. Greater oversampling factors lead to a better visual effect, but may slow down the execution of the function.

Algorithm

The algorithm used by SARSIM2 is derived from the GENSIM function, which is part of SABOTS (SAR Analysis Based On Terrain Simulation) developed by Dr. Bert Guindon of CCRS (Canada Centre for Remote Sensing) in Ottawa, Canada.

Pseudo-geocoding is achieved using the same resampling methodology applied to the geocoding of real imagery. The resulting simulation incorporates all of the inherent spatial ambiguities and radiometric artifacts associated with layover, thereby allowing for direct simulated-to-real image comparisons.

The algorithm used by SARSIM2 can be found in the paper, "Analytic Formulation of Spaceborne SAR Image Geocoding and "Value-Added" Product Generation Procedure Using Digital Elevatoin Data", by B. Guidon and M. Adair. See the References section for details.

For more details about the algorithm used by SARSIM2, refer to the "Algorithm" section in SARSIM1.

References

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.