differences between ISIS and INTI results

Design, construction, tuning of spectroscopes
Information and discussion about softwares (telescope remote, autoguiding, acquisition, spectral processing ...)
Post Reply
Robin Leadbeater
Posts: 1926
Joined: Mon Sep 26, 2011 4:41 pm
Contact:

differences between ISIS and INTI results

Post by Robin Leadbeater »

Olivier Garde has posted a comparison between spectra processed using ISIS and INTI which shows some interesting differences
http://www.spectro-aras.com/forum/viewt ... =70#p16741
2SPOT wrote:
And comparison between ISIS and spec inti process, better resolution and better snr in the blue part of the spectrum because of the way to calibrate the spectrum on each raw image with the [OI] atmospherique line at 5577,35Å with a new method to apply the flat.
Hi Olivier

That is an interesting comparison. Why is the continuum different in the red? There should of course be no difference on the same data. Do you know why? The big question is Which is "right" ?

I am also surprised at the noise at the blue end even at 4000A (due to the flat?). I tested this last year with using my ALPY and ISIS with and without a flat and found less than 1% additional noise from 3800-7800A using a master flat made from a stack of 30 well exposed flats.

Cheers
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Olivier GARDE
Posts: 1243
Joined: Thu Sep 29, 2011 6:35 am
Location: Rhône Alpes FRANCE
Contact:

Re: differences between ISIS and INTI results

Post by Olivier GARDE »

.......
Last edited by Olivier GARDE on Thu Mar 17, 2022 5:41 pm, edited 1 time in total.
LHIRES III #5, LISA, e-Shel, C14, RC400 Astrosib, AP1600
http://o.garde.free.fr/astro/Spectro1/Bienvenue.html
Olivier GARDE
Posts: 1243
Joined: Thu Sep 29, 2011 6:35 am
Location: Rhône Alpes FRANCE
Contact:

Re: differences between ISIS and INTI results

Post by Olivier GARDE »

Hi Robin,

Spec inti, which was designed by Christian Buil and Valérie Desnoux, this software is very different from others in the world of amateur spectroscopy because it is based on a development specific to the practical experience of Christian and Valérie for many years and in Python with many useful functions that you can put in the process as you want.
First design for the Star"Ex, but work fine with others spectrographs like Alpy 600, LISA, LHIRES III and others.

Without going into details, it has lots of very interesting functions such as the registration of raw images with an atmospheric line (for example the [OI] 5577.35 Å line or the method for applying the flat on the spectrum.

Spec inti have 5 differents methods for wavelength calibration.

All the documentation is here (in French only for the moment) :
http://www.astrosurf.com/solex/specinti.html

Multi OS : Mac OS, PC, Linux.

And you can process all spectra from one night in just few minutes, here's the result for 16 targets with Alpy 600 from our setup in Chile.

Image
LHIRES III #5, LISA, e-Shel, C14, RC400 Astrosib, AP1600
http://o.garde.free.fr/astro/Spectro1/Bienvenue.html
Robin Leadbeater
Posts: 1926
Joined: Mon Sep 26, 2011 4:41 pm
Contact:

Re: differences between ISIS and INTI results

Post by Robin Leadbeater »

Hi Olivier,

Yes I know INTI works differently to ISIS but I do not find the problems you are seeing with your ALPY and ISIS (noise even at 4000A and loss of resolution because of stability.) Aligning on a single sky line will work for offsets due to flexure but will not work correctly if the dispersion changes (due expansion with temperature for example).

The difference in the continuum shape concerns me. (I assume it is because of Christian's latest ideas on flats, instrument response and atmospheric extinction) I think we need to understand why the 2 programs give different results.

The problem with ISIS is it is sometimes a "black box" I hope INTI is not like this. To trust software we need it to be well documented so we know exactly how it works and can understand any limitations.

Cheers
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Jacques Michelet
Posts: 16
Joined: Mon Apr 01, 2019 8:13 pm

Re: differences between ISIS and INTI results

Post by Jacques Michelet »

Hi Robin,

As far as I can see, Inti also suffers the "black box" syndrom. Even the Linux version is published as a pre-compiled binary, and not as a Python source code. For sure, binaries are far easier to deploy, since struggling with Python environments may be a real pain for most of us.
But I also fully agree that in order to trust a software, we need to understand what is "under the hood". If we cannot access the source code, we shoud at least get a detailed reference documention. Especially in a scientific domain such as spectroscopy.
And unfortunaltely, the BASS project, Demetra and Isis also belong to the "black boxes" family. All these are great pieces of code, and are developped by really skilled people. But they just miss one point.

Jacques Michelet
Post Reply