AIRS Level 1B Visible/Near-Infrared Channels ATBD - NASA's Earth ...

AIRS Level 1b ATBD Part 2: Vis/Near IR Channels
Figure 1.4: Schematic of the ground location of the visible footprints (squares) relative to the circular
infrared footprints. The along-track direction is towards the top of the page. Three scan lines are shown nearnadir,
for the nominal 705 km orbital altitude. The footprints are only schematic because the surface is
oversampled by the Vis/NIR detectors: there are really 8 across-track samples per infrared footprint, resulting
in each square pixel overlapping by 1/3 with its neighbors to either side. Similarly, each scan line overlaps
with the previous by ~1.57 pixels, but for clarity the figure shows the overlap as only 1 pixel.
Figure 1.4 shows schematically the ground location of the visible footprints relative to the
spectrometer footprints near nadir for three scan lines. In the figure, the spacecraft flight
direction is towards the top of the page, and the three roughly horizontal rows of circles
represent three across-track scans of the instrument. (Spacecraft motion shifts successive
samples in the along-track direction.) Each Vis/NIR detector consists of 9 pixels aligned in
the along-track direction, which are swept across track by the scan mirror. There are
approximately 1.57 pixels of overlap between successive scan lines and eight overlapping
pixels across each infrared footprint. (For simplicity, the scan line overlap is shown as one
pixel, and only six non-overlapping pixels are shown across track for each infrared
footprint.)
Throughout this document, the term “pixel” is used to describe a roughly square region on a
detector, 250 µm on a side. Each pixel, however, is composed of 8 sub-elements, a subelement
being 250 µm in the scan direction, ŷ, but only 25 µm along the array axis, ˆx. The
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