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imagepol.depolratio - Function

	Package	general
	Module	images
	Tool	imagepol

Linear depolarization ratio

Synopsis
depolratio(infile, debias, clip, sigma, outfile)

Arguments

infile	in	Other image
		Allowed:	String or Image tool
debias	in	Debias the linearly polarized intensity ?
		Allowed:	T or F
		Default:	F
clip	in	Clip level for auto-sigma determination
		Allowed:	Float
		Default:	10
sigma	in	Standard deviation of thermal noise
		Allowed:	Float
		Default:	Auto determined
outfile	in	Output image file name
		Allowed:	String
		Default:	Unset

Returns
Image tool or fail

Description

This function (short-hand name dr) returns the linear depolarization ratio computed from two frequencies; this is the ratio of the fractional linear polarization at the two frequencies. Generally this is done when you have generated two images, each at a different frequency (continuum work). Thus if the fractional linear polarization images are m_$\nu$1 and m_$\nu$2 then the depolarization ratio is m_$\nu$1/m_$\nu$2.

This function operates with two images; the first (at frequency $\nu$1) is that with which you constructed your Imagepol tool. The second (at frequency $\nu$2) is supplied via the argument infile, which can be an Image tool, or a String holding the name of the image file.

In generating the depolarization ratio, you may optionally debias the linearly polarized intensity. This requires the standard deviation of the thermal noise. You can either supply it if you know it, or it will be worked out for you with outliers from the mean clipped at the specified level.

You can get the depolarization ratio error image with function sigmadepolratio.

Example

- im1 := image('stokes.4800')
- im2 := image('stokes.8300')
- p := imagepol(im1)
- dpr := p.depolratio(im2);           # m_4800 / m_8300
- edpr := p.sigmadepolratio(im2);