SARBETA

Description

Generates a calibrated radar brightness image from a RADARSAT or ENVISAT ASAR image.

Parameters

Name	Type	Caption	Length	Value range
FILE*	String	Input file name	1 - 192
DBIC*	Integer	Input raster channel(s)	1 - 2
DBIW	Integer	Raster input window	0 - 4	Xoffset, Yoffset, Xsize, Ysize
A0SEG*	Integer	Input SAR offset segment	1 - 1
ASCALSEG*	Integer	Input SAR gain segment	1 - 1
FILO	String	Output file name	0 - 192
DBOC*	Integer	Output raster channel	1 - 1
AMPORDB	String	Amplitude, power, or decibels	0 - 3	AMP \| DB \| POW Default: DB
MONITOR	String	Monitor mode	0 - 3	ON, OFF Default: ON

* Required parameter

Parameter descriptions

FILE

Specifies the name of the file that contains the imagery and segments to use as input. The specified file must contain the SAR Orbital Ephemeris segment.

DBIC

Specifies the image channel(s) to use as the input imagery:

For non-SLC imagery, process one channel
For SLC imagery, process the I and Q channels

For ASAR Alternating Polarization images, only one polarization can be processed at a time.

For Single Look Complex (SLC) images, two channels must be specified.

If two channels are specified, the first channel is taken as the "I" (in-phase or real) channel and the second as the "Q" (quadrature or imaginary) channel of an SLC image. For ASAR Alternating Polarization SLC images, the two specified channels must have the same polarization.

DBIW

Specifies the raster window (Xoffset, Yoffset, Xsize, Ysize) that is read from the input image. If this parameter is not specified, the entire image is processed 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.

If this parameter is specified to a window size smaller than that of FILE, the orbit and array segments contained in FILE will not be output to FILO.

A0SEG

Specifies the segment that contains the input SAR offset array, including the offset value to use to convert image pixel values.

This segment is created when the satellite image is read from CD using CDASAR. It is typically labeled "SAR Offset" or "A0Scale".

ASCALSEG

Specifies the segment that contains the input SAR gain array, consisting of a gain scaling table use to convert image pixel values.

This segment is created when the satellite image is read from CD using CDSAR or CDASAR. It is typically labeled "SAR Gain" or "AScaling".

For ASAR Alternating Polarization images, the input image will contain two SAR Gain channels, with the second layer identified as "SAR Gain, second polarization". Select the array channel that matches the polarization of the specified image layer(s) for processing.

FILO

Specifies the name of the image file to receive the generated brightness image.

If this parameter is not specified, the input file (FILE) is used to store the output image.

The specified output file must already exist, and should be the same size as the input file. The input window defaults to the entire image.

DBOC

Specifies the output image channel to receive the generated brightness image.

The output channel must be 32-bit real.

If the output channel is the same as the specified input channel (DBIC) of the same image file, the output image is processed correctly and overwrites the input image. This is not advised unless the input image channel is 32-bit real.

AMPORDB

Specifies whether to output amplitude, power or decibel (dB) values.

Available options are:

DB: output decibel (dB) values.

Decibels will produce a range of real numbers that may include negative and positive values. If quantitative measurements of radar brightness over point and distributed targets is the objective, AMPORDB should be set to "DB". Because decibel values are on a logarithmic scale, some mathematical operations applied to the dB output channel may not be valid. For example, the averaging of pixels will not yield a correct mathematical result. Any such operations should be performed on either amplitude or power values and the result then converted to dB.
AMP: output amplitude values

Amplitude values (where amplitude equals the square root of the radar brightness or power) have a positive range of real values. If the imagery is to be further processed with filtering or classification, AMPORDB should be set to "AMP".
POW: output power values

Power values (where power equals the radar brightness) would have a positive range of real values.

Data may be converted from decibels to amplitude or power values (or from amplitude or power values to decibels) using the modeling functions or the MODEL function. For more information, see the Algorithm section.

MONITOR

The program progress can be monitored by printing the percentage of processing completed. A system parameter, MONITOR, controls this activity.

Available options are:

ON: Turns the monitor ON (default)
OFF: Turns the monitor OFF (recommended if running in batch or background mode)

Details

SARBETA generates a calibrated radar brightness image from the input scaled radar image (RADARSAR or ENVISAT ASAR) using the SAR offset and scaling.

The input image (FILE) contains the scaled radar image (DBIC), and the offset and gain information stored in array segments (SAR Offset, SAR Gain) to use as input.

An image window to process (DBIW) may be specified. If DBIW is not specified, the entire image is processed.

For ASAR Alternating Polarization images only one polarization can be processed at a time.

Example

In this example, an ASAR Alternating Polarization image is processed.

EASI>file	=	'asarapp.pix'	! input file
EASI>dbic	=	1	! input radar image channel
EASI>dbiw	=		! process entire image
EASI>a0seg	=	3	! SAR Offset segment
EASI>ascalseg	=	4	! SAR Gain segment
EASI>filo	=		! use FILE for output
EASI>dboc	=	2	! output brightness channel
EASI>ampordb	=	'AMP'	! output amplitude image

EASI>run SARBETA

Algorithm

For a single input channel, the radar brightness is calculated as follows:

If the output is in decibels (when AMPORDB="DB" or AMPORDB=):
```
Bij = 10.0 * log10( (DN*DN + A0)/Aj )
```
If the output is in amplitude values (when AMPORDB="AMP"):
```
Bij = sqrt( (DN*DN + A0)/Aj )
```
If the output is in power values (when AMPORDB="POW");
```
Bij = ( (DN*DN) +A0)/Aj )
```
where:
- Bij: the output brightness for scanline i, pixel j. (When AMPORDB="AMP", Bij is the square root of the radar brightness.)
- log10(): the logarithm base 10 function
- sqrt(): the square root function
- DN: the input image value for scanline i, pixel j
- A0: the gain offset from the first member of A0SEG
- Aj: the expanded gain scaling table value for column j

If there are two input channels, the first is taken as the I (in-phase or real) channel and the second as the Q (quadrature or imaginary) channel for a complex number.

The radar brightness is calculated as follows:

If the output is in decibels (when AMPORDB="DB" or AMPORDB=):
```
Bij = 10.0 * log10( (DNI*DNI + DNQ*DNQ)/(Aj*Aj) )
```
If the output is in amplitude values (when AMPORDB="AMP"):
```
Bij = sqrt( (DNI*DNI + DNQ*DNQ)/(Aj*Aj) )
```
If the output is in power values (when AMPORDB="POW"):
```
Bij = ( (DNI*DNI +DNQ*DNQ)/(Aj*Aj) )
```
where:
- Bij: the output brightness for scanline i, pixel j. (When AMPORDB="AMP", Bij is the square root of the radar brightness.)
- log10(): the logarithm base 10 function
- sqrt(): the square root function
- DNI: the input image I value for scanline i, pixel j
- DNQ: the input image Q value for scanline i, pixel j
- Aj: the expanded gain scaling table value for column j
For information on the calculations shown above, refer to the papers cited in the References section.

Decibels can be converted to amplitude values using the following model:

 model
     %1 = (exp10( %2 / 10.0 ))^0.5
 endmodel

where:

%1: the output amplitude values written to channel 1
exp10(): the base 10 exponential function
%2: the input decibel values read from channel 2
()^0.5: the square root of the value

Amplitude values can be converted to decibels using the following model:

 model
     %2 = 10.0 * log10( (%1)^2 )
 endmodel

where:

%2: the output decibel values written to channel 2
log10(): the logarithm base 10 function
(%1)^2: the square of the input amplitude read from channel 1

Amplitude values can be converted to power values using the following model:

 model
     %2 = %1^2
 endmodel

where:

%2: the output power value written to channel 2
%1^0.5: the square of the input amplitude read from channel 1

Power values can be converted to amplitude values using the following model:

 model
     %2 = %1^0.5
 endmodel

where:

%2: the output amplitude value written to channel 2
%1^0.5: the square root of the input power read from channel 1

Acknowledgements

PCI Geomatics received financial support for the enhancement of this software through the Earth Observation Applications Development Program (EOADP) of the Canadian Space Agency/L'Agence Spatiale Canadienne, under contract No. 9F028-2-4917/14.

References

N.W.Shepherd and Associates, (February 26, 1996). 4.2 Calibration Equation for Detected Products. In Technical Note No. 4.2 CDPF Output Data Calibration (p. 9).

N.W.Shepherd and Associates, (February 26, 1996). 4.3 Calibration Equation for SLC Products. In Technical Note No. 4.2 CDPF Output Data Calibration (p. 9).

Environments	PYTHON :: EASI :: MODELER
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SARBETA

Generate radar brightness

Description

Parameters

Parameter descriptions

Details

Example

Algorithm

Acknowledgements

References