Calculates polarisation parameters
TRUE
value for Parameter
VARIANCE.
By default, three output NDFs are created holding percentage polarisation, polarisation angle and total intensity. However, NDFs holding other quantities, such as the Stokes parameters, can also be produced by overriding the default null values associated with the corresponding parameters. The creation of any output NDF can be suppressed by supplying a null value for the corresponding parameter.
There is an option to correct the calculated values of percentage polarisation and polarised intensity to take account of the statistical bias introduced by the asymmetric distribution of percentage polarisation (see Parameter DEBIAS). This correction subtracts the variance of the percentage polarisation from the squared percentage polarisation, and uses the square root of this as the corrected percentage polarisation. The corresponding polarised intensity is then found by multiplying the corrected percentage polarisation by the total intensity. Returned variance values take no account of this correction.
TRUE
if a correction for statistical bias is to be
made to percentage polarisation and polarised intensity. This correction cannot be used if
any of the input NDFs do not contain variance values, or if you supply a FALSE
value for
Parameter VARIANCE. [FALSE]
[!]
[!]
[!]
[!]
[!]
TRUE
if output variances are to be calculated. This
parameter is only accessed if all input NDFs contain variances, otherwise no variances are
generated. [TRUE]
A bad value will appear in the output data and variance arrays when any of the four input data values is bad, or if the total intensity in the pixel is not positive. The output variance values are also undefined when any of the four input variances is bad or negative, or any computed variance is not positive, or the percentage polarisation is not positive.
If the four input NDFs have different pixel-index bounds, then they will be trimmed to match before being added. An error will result if they have no pixels in common.
The output NDFs are deleted if there is an error during the formation of the polarisation parameters.
The output NDFs obtain their QUALITY, AXIS information, and TITLE from the IN1 NDF. The following labels and units are also assigned:
I | "Total Intensity" | UNITS of IN1 |
IA | "Total Intensity" | UNITS of IN1 |
IB | "Total Intensity" | UNITS of IN1 |
IP | "Polarised Intensity" | UNITS of IN1 |
P | "Percentage Polarisation" | "%" |
Q | "Stokes Q" | — |
U | "Stokes U" | — |
THETA | "Polarisation Angle" | "Degrees" |
This routine correctly processes the AXIS, DATA, QUALITY, VARIANCE, LABEL, TITLE, UNITS, WCS, and HISTORY components of the input NDF and propagates all extensions.
Processing of bad pixels and automatic quality masking are supported.
All non-complex numeric data types can be handled. Arithmetic is performed using single-precision floating point.