| wavelength calibration [message #69965] |
Fri, 19 February 2010 21:38  |
sid
Messages: 50
Registered: January 1995
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Member |
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Hi,
Please give some tips and suggesions on wavelength calibration for
spectral data
regards
sid
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| Re: wavelength calibration [message #78211 is a reply to message #69965] |
Thu, 03 November 2011 13:05  |
rogass
Messages: 200
Registered: April 2008
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Senior Member |
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On 1 Nov., 15:08, Gray <grayliketheco...@gmail.com> wrote:
> Hello IDL gurus,
>
> I have a night-sky emission spectrum (from my data), and a list of
> irregularly-gridded night-sky lines (from the literature). I'm trying
> to perform a wavelength calibration of my data; I have a quite poor
> zeroth-order solution already.
>
> My best idea so far was to perform a cross-correlation of the two data
> sets to find the wavelength shift and then do some least-squares
> fitting to find a better solution. However, I'm not sure how to
> perform the cross-correlation.
>
> My data is in the form:
> (a) n-element array of spectrum data points
> (b) n-element array of zeroth-order wavelengths
> (c) m-element array of night-sky emission line wavelengths (irregular)
> (d) m-element array of night-sky emission line strengths
>
> So my questions are:
> 1) How do I compute the cross-correlation between these two sets of
> data?
> 2) Is this the best way to go about it?
>
> Thank you as always...
> --Gray
Hi,
2) it depends on :)
Just look for smile correction, e.g.:
with known endmember:
Guanter, L., Segl, K., Sang, B., Alonso, L., Kaufmann, H., Moreno, J.
(2009): Scene-based
spectral calibration assessment of high spectral resolution imaging
spectrometers. - Optics
Express, 17, 14, 11594-11606, DOI: 10.1364/OE.17.011594
with atmospheric absorptions:
Richter, Rudolf und Schläpfer, Daniel und Müller, Andreas (2011)
Operational atmospheric correction for imaging spectrometers
accounting for the smile effect.
IEEE Transactions on Geoscience and Remote Sensing, 49 (5), Seiten
1772-1780.
IEEE. DOI: 10.1109/TGRS.2010.2089799.
It's pretty simple to implement. Just use SHARP features.
Cheers
CR
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| Re: wavelength calibration [message #78242 is a reply to message #69965] |
Tue, 01 November 2011 12:41 |
Brian Wolven
Messages: 94
Registered: May 2011
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Member |
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The approach I've used is to perform a windowed cross-correlation of the observed spectrum with a synthetic spectrum, e.g., one generated from a line list. The exact window shape and size would depend on what your spectra look like; mine are essentially gaussians centered on the positions of the known strong emission lines. I then perform a low-order polynomial fit to the wavelength/spectral bin coordinate pairs obtained from the set of cross-correlations. In order for this approach to work well you need to have a pretty good handle on your instrument's line shape/PSF, as you'll probably want to convolve that shape with your synthetic line positions before doing the cross-correlation.
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| Re: wavelength calibration [message #78243 is a reply to message #69965] |
Tue, 01 November 2011 12:24 |
Jeremy Bailin
Messages: 618
Registered: April 2008
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Senior Member |
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On 11/1/11 10:08 AM, Gray wrote:
> Hello IDL gurus,
>
> I have a night-sky emission spectrum (from my data), and a list of
> irregularly-gridded night-sky lines (from the literature). I'm trying
> to perform a wavelength calibration of my data; I have a quite poor
> zeroth-order solution already.
>
> My best idea so far was to perform a cross-correlation of the two data
> sets to find the wavelength shift and then do some least-squares
> fitting to find a better solution. However, I'm not sure how to
> perform the cross-correlation.
>
> My data is in the form:
> (a) n-element array of spectrum data points
> (b) n-element array of zeroth-order wavelengths
> (c) m-element array of night-sky emission line wavelengths (irregular)
> (d) m-element array of night-sky emission line strengths
>
> So my questions are:
> 1) How do I compute the cross-correlation between these two sets of
> data?
> 2) Is this the best way to go about it?
>
> Thank you as always...
> --Gray
If you want to go the cross-correlation route, you should probably
create a fake spectrum from your wavelength table that has single-pixel
peaks of the amplitudes (d) at the locations (c), resample them both to
a higher identical spectral resolution, and then cross-correlate those.
As for a better solution, you could try specifying a mapping function
lambda_true(lambda_0) that's perhaps a simple polynomial and use that to
map the wavelengths (b) before doing the resampling step, and then
maximize the cross-correlation-max-amplitude with respect to the
parameters of the polynomial.
-Jeremy.
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