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[Miscellaneous #UFF-250801]: GOES east & west geotiff files



Hi Derek,

re:
> One more question regarding the 3-hourly updates.  How close to real time
> are they?  For instance, if an image is updated at noon, is that image from
> just before noon, or is it actually from earlier in the morning?  My
> supervisor wanted me to verify that first off.

The nominal time assigned to the composite is within the hour for the GOES
full disk scans (which are made every three hours) of that hour.  The other
portions of the composite (which come from other geostationary platforms
like METEOSAT and from polar orbiters) are as close to the nominal time as
possible.  The challenge in creating a composite from so many satellites
is that the satellites do not scan at the same time, for instance, GOES-East
(currently GOES-13) scans at H+15 and H+45 for North American coverage and
GOES-West (currently GOES-15) scans at H+00 and H+30 for its North American
coverage.  Given this, there is automatically at least a 15 minute time
difference in the GOES portions of the composites, and this gets "worse"
for other satellites especially the polar orbiters.  The other trick thing
is that the nominal time associated with a scan is what is thought to be
a representative time.  The reason for this is that it takes a measurable
amount of time to do an entire scan (CONUS, North American, Full Disk,
Rapid Scan, etc.), so the time associated with each pixel in a scan is different
from every other pixel in the same scan (i.e., scans are not snapshots
of the coverage like photos are).  This time difference from pixel to pixel
(albeit very small for neighboring pixels) is the biggest reason that satellite
images are fundamentally different from model output where the time associated
with each grid point is fixed.

Given your description of what you want the global composites for (public
outreach only), I am a bit curious why the time associated with a composite
is of such interest.  Can you help me understand the issues?

BTW, I will be putting the CentOS virtual machine I have out on FTP when
I get into work (I'm at home at the moment).

Cheers,

Tom
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Ticket Details
===================
Ticket ID: UFF-250801
Department: Support McIDAS
Priority: Normal
Status: Closed


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