| Re: AVHRR Image Mapping Problem [message #51975 is a reply to message #51852] |
Sun, 17 December 2006 20:05   |
James Kuyper
Messages: 425
Registered: March 2000
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Senior Member |
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Richard G. French wrote:
...
> If one trusted the data headers from Hubble Space Telescope images as a
> guide to where the spacecraft was actually pointed, one would be up to 10
> pixels off - that's because what's listed in the header is where they
> expected to be pointing, not a reconstructed view of where they were
> actually pointing. The same is true of Cassini images of Saturn. I don't
> know about Earth-pointing satellites, but unless one has done some pretty
> accurate post-image checking, it is not obvious to me that the header
> information for such an image would have anything other than the predicted
> location of the image,
I only know about one instrument (MODIS) on two Earth-pointing
satellites (Terra and Aqua), but I'm personally responsible for the
geolocation on the MODIS data from those satellites. The file
attributes summarizing the location of a granule are just as accurate
as the geolocation which is provided in the MOD03 files for every 1km
pixel: the RMS error is nominally 50 meters, though we're actually
doing a bit better than that, with our smallest pixel size being 250
meters. Except during a maneuver, the actual orientation of the
satellite is used, not the planned orientation.
The software I'm responsible for was modified from software for earlier
instruments, and has been borrowed as the basis for sofware for the
VIIRS instrument on NPP, so I suspect this is not uncommon for
earth-pointing satellite imagery.
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