VIIRS Basics

Here is some basic information about VIIRS (Visible Infrared Imaging Radiometer Suite). VIIRS is a scanning radiometer with 5 high-resolution Imagery bands (or I-bands), 16 Moderate resolution bands (M-bands) and a Day/Night band (DNB). The Suomi NPP platform is in the same orbital plane as the A-Train constellation but at a higher altitude. The A-Train platforms have an orbital altitude of 705 km, while the Suomi NPP platform has an orbital altitude of about 824 km. The A-Train and Suomi NPP polar-orbiting platforms are sun synchronous with an equator crossing time of 1330 (local time).

A rotating mirror reflects radiation onto a set of CCD detectors; a single scan relates to a rotation of the mirror. A single VIIRS scan is completed in 1.779 seconds - the mirror rotation rate is slightly faster than the spec but is within tolerance. The M bands and the day/night band have 16 detectors per scan (750 m spatial resolution per pixel), while the I bands have 32 detectors per scan (375 m resolution per pixel).

There are some differences between MODIS and VIIRS. All MODIS bands had single gain, while there are multiple VIIRS solar bands that have dual gain. The day/night band has multiple gains depending on moonlight conditions. Another difference between MODIS and VIIRS is the swath width. VIIRS has a swath of about 3040 km in the cross-track direction while MODIS has a swath width of 2330 km. With VIIRS, there are no coverage gaps in the Tropics as there are with MODIS.

Dr. Curtis Seaman (CIRA/Colorado State University) has prepared a very nice Beginner's Guide that provides some useful background. He and his colleagues are turning this into a NOAA Technical Report although it is still in draft form.

VIIRS Bands (I: Imagery; M: Moderate resolution)