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

sarsim2(file, dbec, dboc, dbiw, escale, alti, head, minlook, nrpoint, oversamp)

Name	Type	Caption	Length	Value range
FILE *	str	Input DEM file name	1 -
DBEC *	List[int]	DEM raster	1 - 1
DBOC *	List[int]	Output simulated SAR image channel	1 - 1
DBIW	List[int]	Input window	0 - 4	Xoffset, Yoffset, Xsize, Ysize
ESCALE	List[float]	Elevation scale and offset (m)	0 - 2	Default: 1,0
ALTI *	List[float]	Sensor altitude (m)	1 - 1	0 -
HEAD	List[float]	Sensor azimuth (degrees)	0 - 1	0 - 360 Default: 0
MINLOOK *	List[float]	Minimum look angle (degrees)	1 - 1	0 - 90
NRPOINT	List[float]	Near range point on DEM (easting, northing)	0 - 2
OVERSAMP	List[int]	Oversampling factor	0 - 1	3 - 15 Default: 5

* Required parameter

Parameter descriptions

FILE

Specifies the name of the input file that contains the elevation channel.

DBEC

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.

DBOC

Specifies the 16-bit unsigned output image channel to receive the simulated SAR image.

DBIW

Optionally specifies the raster window (Xoffset, Yoffset, Xsize, Ysize) read from the input elevation channel.

If this parameter is not specified, the entire layer is used by default. Xoffset, Yoffset define the upper-left starting pixel coordinates of the window. Xsize is the number of pixels that define the window width. Ysize is the number of lines that define the window height.

ESCALE

Optionally specifies the scale and offset to apply to the elevation values in the input elevation channel, to convert values to meters. If this parameter is not specified, scale defaults to 1, and offset defaults to 0.

The equation for the conversion is:

elevation in meters = scale * (value + offset)

For example, to convert elevation values from feet to meters, where a value of 0 represents 1000 feet:

0.3048,1000        | meters = 0.3048 * (value + 1000)

ALTI

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

HEAD

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).

MINLOOK

Specifies the minimum range look angle, in degrees.

NRPOINT

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.

OVERSAMP

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.

This function uses the elevation data (DEM) from a specified input channel (DBEC) under a defined window area (DBIW) to generate a pseudo-geocoded simulated SAR image. The simulated image is stored in the specified output channel (DBOC). The function also generates shadow and layover areas, which are stored as two separate output bitmaps.

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.

Example

Create a pseudo-geocoded simulated ERS-1 image from the elevation data stored on channel 10 of the file 'irvine.pix'. First use PCIMOD to create a 16-bit unsigned channel on 'irvine.pix'. Then, run SARSIM2 to create the simulated radar image in channel 12. ALTI and MINLOOK are set to appropriate values for coarse resolution ERS-1 data, and HEAD is set to the approximate heading angle for an original ERS-1 image, which this is intended to simulate. In this case, SARSIM2 creates a 512 pixel x 512 line 16-bit unsigned image, stored on channel 12 of irvine.pix. Compare this with the geocoded ERS-1 image in channel 11.

from pci.pcimod import pcimod
from pci.sarsim2 import sarsim2

file	=	'irvine.pix'
pciop	=	'ADD'
pcival	=	[0,0,1,0]	# add 16-bit unsigned channel

pcimod( file, pciop, pcival )

dbec	=	[10]	# input elevation channel
dboc	=	[12]	#new 16-bit unsigned channel
dbiw	=	[]	# default; process entire image
escale	=	[]
alti	=	[784000]	# altitude above sea level (m)
head	=	[]	# heading angle (degrees) default 0.0
minlook	=	[17.7]	# minimum look angle (degrees)
nrpoint	=	[]	# default; upper-left corner
oversamp	=	[]	# oversampling factor; default 5

sarsim2 ( file, dbec, dboc, dbiw, escale, alti, head, minlook, nrpoint, oversamp )

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.