AIRS

Frequently Asked Questions


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Q.  How can I know the exact satellite overpass time for each pixel?   

A.  The AIRS Level 3 Daily Product is produced through binning and
gridding the concatonation of AIRS Level 2 products for a day. Thus,
if there is more than a single datum in the 1 deg x 1 deg bin, as
happens when polar orbital swaths overlap (happens beginning at |lat|
> 35 deg), the time associated with that bin is a range (which becomes
greater with increasing latitude).

The 1:30 PM local time for ascending is the nominal Equator crossing
time going from South to North. The only correct way to determine the
exact time an observation included in the bin was made is to look at
the Level 2 Data Product. Contained therein is the start time of a
granule, and it is a simple calculation to calculate the exact time a
particular footprint (MW, IR, vis/NIR) was observed from its position
in the granule (scanline and footprint within scanline). The duration
of a granule is exactly 6 minutes (45 AMSU scans - 8 seconds/scan; 135
AIRS scans - 2.6667 seconds/scan; 30 AMSU footprints/scan; 90 AIRS
footprints/scan).

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