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Re: array subtraction [message #63344 is a reply to message #63342]

Wed, 05 November 2008 07:58

R.Bauer
Messages: 1424
Registered: November 1998

Senior Member

julia.walterspiel@gmail.com schrieb:
> hey guys
> SOS call from the newbie:
>
> I've got two data arrays, one of length 134 (=a), the other of length
> 75 (=b) with monthly cloud cover data from modis terra and aqua.
> Data from Terra starts feb 2000, data from Aqua starts july 2002.
>
> I want to calculate and plot the difference in cloud cover for each
> month from Terra and Aqua. so far so good.
>
> the two data arrays are "connected" by two (separate) time arrays c
> (for Terra, feb 2000 - now) and d (for Aqua july 2002 - now).
> that means, my data array "b" starts only somewhere at index so-and-so
> of "a" (not sure where exactly).
> Now, how can I tell IDL to subtract the two arrays at the right point,
> meaning subtract the terra-value on july 2002 from the aqua value on
> the same date?
>
> I'm sure everyone of you can do that with both eyes closed and it
> can't be difficult but I couldn't find any help online.
> thanks!
> juls

Hi Julia

no not with both eyes closed. It is not easy to give a correct answer.
Well you can substract appels from bananas but this will make no sense.

if the data does not change very fast on a better time resolution you
may want to interpolate the data of one table to the other ones time
base. And you can cut off the region where you don't have a close
mapping in time.

If the data does have a big variation in a better time resolution you
should not interpolate. Then you can create for example a mean value for
each month.

cheers
Reimar

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[Message index]

		Re: array subtraction By: Spon on Wed, 05 November 2008 08:39
		Re: array subtraction By: Wout De Nolf on Wed, 05 November 2008 08:29
		Re: array subtraction By: Brian Larsen on Wed, 05 November 2008 08:29
		Re: array subtraction By: julia.walterspiel on Wed, 05 November 2008 08:15
		Re: array subtraction By: R.Bauer on Wed, 05 November 2008 07:58
		Re: array subtraction By: julia.walterspiel on Mon, 10 November 2008 07:59

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