Subtracting one dataset from another?

[Gasman]

Hi folks

I`m trying out a fibre optic spectrometer for taking spectra. The software gives results in .csv format like so -

This is a screenshot from the scope with cap fitted ie just noise call it plotA-

This is a screenshot from the scope with cap removed pointing at Jupiter call it plotB

Now somewhere in plotB is the data of Jupiter and I gather software such as Excel or Openoffice can subtract the data in plotA from plotB but I`m not sure how to go about it if someone could point me to a tutorial or suchlike please?. I assume its just like subtracting a Dark from a Light in ccd imaging!.

cheers

Steve

[perfrej]

Well, you have the data in text format, a format which Excel (or the OpenOffice equivalent). Import it, add a column with the calculated data and plot it. Should be straight forward

/per

[Macavity]

Hmmm... The data does look a bit similar to the background though. [teasing]

A fair bit of random noise on both? BUT I do sense there are real differences.

Perhaps a bin-by-bin subtraction won't reveal too much. I also imagine you do 

want to preserve the SHARP resolution of the data? Maybe take a leaf from

LHC / Higgs Physics book and *smooth* the background before "subtraction"?

http://www.atlas.ch/news/images/stories/1-plot.jpg (Show stuff as superimposed plots etc.)

It's all more about data presentation... Guiding the eye to the intended result?

[Gasman]

Thanks Per and Chris, at this point I`m not 100% the scope (or rather the fibre) was bang on Jupiter, I need to tweak the flip mirror a bit more, its more the practical side of the data subtraction I was trying to suss out not having a great deal of experience with spreadsheets.

I`ve got both files loaded in the spreadsheet with a couple of not needed columns deleted like so

So the capped scope is columns A to E and the uncapped one in columns I to L with columns A and J the same (the pixel count).

The `Average spectrum` columns seem to be the important ones, so I need to subtract everything in column E from everything in column L and place it in its respective row in say column N but what expression would I need to write in the `function` space at the top to do that please?

Phew need a lie down

Steve

[Bizibilder]

Simply enter    =L6-E6       into cell N6 and press enter.  Then fill down to put the formula in every cell of column N.  You must have the = sign at the beginning of the formula and you must press enter after typing it into the cell.

[Gasman]

Ah! cheers for that, I was missing the ruddy = sign!. I just couldn't get the cells to do anything, easy when you know how ;-)

Steve

[perfrej]

Hey, you need an Excel crash-course. Get one on the net, spend an hour getting to know the stuff and then go at the real problem!

/per

[NickK]

I note that one is 500ms and the other is 800ms (something looked odd - call it spider sense!).. should the noise also be 800ms integration time?

[Gasman]

Thanks for the comments guys,yes there is a difference in the two files which didn't occur to me before, more work to do methinks ;-)

Steve

PS at least I know how to subtract data files now !!