• VIIRS is a scanning radiometer
– As the satellite orbits the Earth, VIIRS scans a swath that is ~3040 km wide (the
cross-track direction).
• Wide enough to prevent data gaps near the Equator (c.f. MODIS)
– A rotating mirror reflects radiation onto a set of CCD detectors. One rotation
of the mirror is one scan.
• M-bands and the DNB have 16 detectors to detect this radiation (16 rows of pixels per
scan)
• I-bands have 32 detectors (32 rows of pixels per scan), with twice the resolution of the
M-bands and the DNB
• Each scan produces a strip of data ~3040 x ~12 km in size
– 48 scans comprise one “granule” of data. One granule represents ~85 seconds
of data collected (~570 km in the along-track direction)
– As a result, each granule covers an area ~3040 x ~570 km in size
• Data is distributed as individual granules*
– There has been some discussion about combining data from several granules
into a single file, but these files would likely be prohibitively large for most
users*
* NOAA CLASS does distribute multiple granules combined into a single file and these files
are huge. Other known data sources (see slide 31) keep each granule in separate files.