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Purpose

 

This panel enables to set the default processing parameters, which are used in those functions where the geocoding processes are executed.

 

Technical Note

 

Radiometric Calibration ("True Area" approach)        

In order to precisely estimate the scattering area, the input DEM is oversampled; the amount of DEM pixels falling in the original SAR geometry within the corresponding cell, determines the scattering area.

 

Radiometric Normalization ("Semi-empirical correction" approach)        

The backscatter dependency from the range position and from the topography is estimated by computing a linear regression between the cosine of the local incidence angle and the backscattering coefficient in logarithmic form. In order to compute the regression, a certain number of pixel samples are collected; the amount of samples can be defined on the basis of the following criteria:

 

▪Minimum value in dB

Only pixels with backscatter coefficient above this threshold are considered.

 

▪Maximum value in dB

Only pixels with backscatter coefficient below this threshold are considered.

 

-Azimuth Sampling Factor

It defines the sampling frequency (in pixels) in azimuth direction.

 

-Range Sampling Factor

It defines the sampling frequency (in pixels) in range direction.

 

Parameters - Geocoding

 

Radiometric Calibration

By setting this flag the calibration is executed. This flag must be checked also when the "Normalized Radiometric Calibration" is selected.

 

Radiometric Normalization

By setting this flag the backscatter coefficient is normalized for variations related to the position in range direction and the topography.

 

Scattering Area Method

The radiometric calibration process can be executed by following two different approaches:

 

➢Local incidence angle - this is the fastest approach in terms of processing time, but it is not the most accurate way to calibrate the data in presence of topography.

 

➢True area - it requires more computing resources, but it is the most accurate approach to calibrate the data in presence of topography. It makes sense to apply this method when a good (in terms of quality and spatial resolution) Digital Elevation Model is available.

 

Max Calibrated Value

The maximum admitted value for calibrated data can be set. Values higher than this threshold, which can eventually be reported on calibrated data for strong local scatterers, are automatically transformed into the specified "Max Calibrated Value". In case any output calibrated value is admitted, this threshold must be set lower than 1.

 

Area Exponent

The exponent value that are given to the scattering area parameter.

 

Normalization Factor

This value should be increased proportionally to the difference between the near and the far range Incidence Angle. The default setting (i.e. 2) is valid for ERS-like acquisition geometries.

 

Normalization Angle

If it is set to negative values, the Incidence Angle in the scene center is used. Any other positive value can be specified.

 

Local Incidence Angle

By setting this flag the map of the local incidence angle – in degree – is generated.

 

Resampling Method

By setting the relevant flag, the interpolation method is specified.

 

Nearest Neighbour        

 

Bilinear Interpolation

 

3rd Order Cubic Convolution

 

4th Order Cubic Convolution

Optimal Resolution

 

Calibration Unit Sigma Nought

It is the backscattering coefficient; the value in dB is usually adopted as conventional measure of the strength of radar signals reflected by a distributed scatterer. The Sigma Nought corresponds to the Beta Nought normalized with the scattering area (i.e. sine of the incidence angle).

In SARscape it is typically presented in linear units; the corresponding value in dB can be calculated as: 10*log10 (calibrated pixel linear value). It is a normalized dimensionless number, which compares the strength observed to that expected from an area of one square meter. It is defined with respect to the nominally horizontal plane, and in general has a significant variation with incidence angle, wavelength, and polarization, as well as with properties of the scattering surface itself.        

 

Calibration Unit Gamma Nought

It is the backscattering coefficient normalised (i.e. divided by) with the cosine of the incidence angle.

 

Calibration Unit Beta Nought

It is the radar brightness (or reflectivity) coefficient. This reflectivity per unit area - in slant range - depends on the system calibration only and it is dimensionless. This value is independent from the local incidence angle; it is obtained by applying the radar equation without considering the scattering area.

 

 

General Functions

 

Load Preferences

It allows loading specific Preferences tthirteen different settings  as possible alternative default processing values.

 

Load

It allows loading an .xml, .sml or .txt file where SARscape common Preferences where previously saved.

 

Save

It allows saving SARscape common Preferences for a future processing using the same preferences characteristics.

 

Help        

Specific help document section.

 

 

Ok        

The selected default processing parameters are loaded.

 

Cancel        

The window will be closed.

 

Specific Function(s)        

 

None.

 

References

 

None.