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Re: mapping/interpolation from one irregular grid to another (different) irregular grid. [message #79007]

Thu, 26 January 2012 01:30

Maarten[1]
Messages: 176
Registered: November 2005

Senior Member

On Jan 24, 10:04 pm, Paul van Delst <paul.vande...@noaa.gov> wrote:
> I have a colleague who wants to map/interpolate data from one satellite sensor's footprint to another. The data is
> defined in terms of pixel vs scan line which means the lat/lon grid (which is how the sensor FOVs are matched) for each
> is quite irregular. He has performed loops over individual elements to do the interpolation, but as you would expect,
> this is very slow in IDL. We need to speed it up (a lot).

Which instruments are we talking about? I mapped MODIS on Aqua to OMI
on Aura within the A-train. Although both grids are irregular, at
least you know that they will pass over the same coordinate within a
fixed time-difference. Both use TAI93 for time-stamping, once you know
that, you can reduce the amount to data to a time-slice of about 10
seconds.

The key thing is to reduce the number of pixels as quickly as
possible. For MODIS -> OMI I used the time difference, then searching
in the 5x5 km pixels, and finally using that to search the 1x1 km
pixels. That took the time down to about 45 minutes per orbit (from
the brute force three weeks). That was good enough for me.

I used the pixels centers for MODIS, and constructed pixel boundaries
for OMI. The IDLanROI class is useful, I created a subclass to deal
with the dateline.

> My first thought would be to put both on a common regular grid, do the matchup/interpolation, and then somehow use
> histogram with the reverse_indices trick to get the matched data back to the irregular grid (as detailed in JD's
> histogram tutorial on idlcoyote.com).
>
> Does any of this make sense? I wanted to poll the IDL users out there that may have done this before recommending my
> colleague embark on a a potential fruitless endeavour.

Going to a regular grid first will introduce all kinds of
interpolation artifacts. So, no it doesn't make sense to me. But it
strongly depends on what you need to do, what instruments we're
talking about (relative pixel sizes in particular). Is there any
relation between the instruments?

Maarten

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[Message index]

		Re: mapping/interpolation from one irregular grid to another (different) irregular grid. By: Maarten[1] on Thu, 26 January 2012 01:30
		Re: mapping/interpolation from one irregular grid to another (different) irregular grid. By: Dick Jackson on Tue, 24 January 2012 23:38
		Re: mapping/interpolation from one irregular grid to another (different) irregular grid. By: Klemen on Tue, 24 January 2012 15:54
		Re: mapping/interpolation from one irregular grid to another (different) irregular grid. By: David Fanning on Tue, 24 January 2012 14:21
		Re: mapping/interpolation from one irregular grid to another (different) irregular grid. By: Paul Van Delst[1] on Thu, 26 January 2012 08:53

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