DER_SNR?

[Petr Skoda]

Dear Kelle,

What spectrograph is it - echelle ?

The DER_SNR is a algorithm which is not only recommended in SDM (about 
2008) but also in various spectrographs simulators... (e.g. MOES)
One of my student used it many years ago and it seemed to be able to work 
well in many cases os single order spectra ...

But it may be quite complicated in case of echelle spectra due to the 
blaze function (the SNR is varying along or individual orders).
The SNR will be also faked by pipeline reduction (e.g. dividing by 
extracted flat field to unblaze the echelle order)

The DER_SNR is 
working only in certain cases (described in the paper
https://adsabs.harvard.edu/full/2008ASPC..394..505S
the STECF newsletter paper does not exists probably - links at many 
places are bad.)

But despite this, it is so far the only one method that is reasonably 
general. But concerning the VO - it is the officially suported 
recommendation to use it in SDM

(in SDM1.2 it is chapter 5.3.1
https://www.ivoa.net/documents/SpectrumDM/20231215/REC-SpectrumDM-1.2-20231215.pdf


So IMHO it is correct to use this FITS KW as it directly maps to SDM in 
the recommended way.

Best regards,

Petr Skoda


On Wed, 16 Apr 2025, Kelle Cruz via dm wrote:

> Date: Wed, 16 Apr 2025 20:36:31
> From: Kelle Cruz via dm <dm at ivoa.net>
> Reply-To: Kelle Cruz <kellecruz at gmail.com>
> To: dm at ivoa.net
> Subject: DER_SNR?
> 
> Hi folks,
>
> I'm working on a new data reduction pipeline and trying to get the output
> spectra to comply with SpectrumDM1.2.  I'm currently having a struggle
> convincing the team to use the "DER_SNR" FITS keyword to store the
> calculated SNR of a spectrum.  Some people are worried that using this
> keyword will imply that a specific algorithm was used to calculate the SNR.
> Specifically, this one: http://www.stecf.org/software/ASTROsoft/DER_SNR/.
> Anyone care to comment on this?
>
> Thanks,
> Kelle
>
> --
> Kelle Cruz, PhD (she/her, they/them)
> Assoc. Professor, Physics and Astronomy, Hunter College
> CEO, ScienceBetter Consulting, LLC
> CFO, Startorialist, Inc. <http://shop.startorialist.com>
> Editor-in-Chief, AstroBetter Blog and Wiki <http://astrobetter.com>
> Research Associate, American Museum of Natural History
> Visiting Scholar, Flatiron Institute
>

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*  Petr Skoda                         Tel   : (323) 649201, l. 361      *
*  Stelarni oddeleni                          (323) 620361              *
*  Astronomicky ustav AVCR, v.v.i     Fax   : (323) 620250              *
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*  Ceska republika                                                      *
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