VIIRS Pass Frequency

GINA collects satellite data around the clock from the satellites that pass over Alaska every day. This graphic shows the number of VIIRS infrared passes received each day by GINA’s Direct Broadcast antennas. The North Slope of Alaska into the Arctic Ocean is the most frequently covered area, with around 16-18 passes per day. Radiating outwards, the frequency of coverage decreases, until hitting zero around the Lower 48-Canadian Border, Hudson Bay, and the Koreas.

A mosaic graph on the frequency of VIIRS infrared (IR) coverage for a given area. Example taken from 20:02 UTC, 3 June 2022

And this graphic is only one out of many. While the one above is specific to the VIIRS Infrared frequency for June 3, 2022, there are over a dozen other bands and countless other days that could be featured.
The pass frequency graph for VIIRS visible data shown below illustrates that the frequencies are very similar in the far northern latitudes because there is much more sunlight this time of year, however there are lower frequencies farther south where there’s less daylight. Come winter, we’d expect this situation to be reversed, showing a significant decrease in frequencies in the northern latitudes (compared to the IR) and higher frequencies in the southern ranges.

A mosaic graph on the frequency of VIIRS visible (VIS) coverage for a given area. Example taken from 20:02 UTC, 3 June 2022

The bar graphs show the frequency of satellite pass data acquisition times by hour for the entire range of GINA’s antennas. These are plotted by satellite type, showing there’s a gap in VIIRS data between 03-08 UTC, AVHRR data between 11-14 UTC, and MODIS between 17-18 UTC. The graphs don’t provide any information about coverage, just the times when antennas start receiving data.

VIIRS Pass Frequency by Hour

AVHRR Pass Frequency by Hour

MODIS Pass Frequency by Hour

The VIIRS satellites received are NOAA-20 and S-NPP. AVHRR satellites received are Metop-B, Metop-C, NOAA-19, and NOAA-18. MODIS satellites received are Aqua and Terra.

AVHRR data helps to fill the gap in VIIRS data during that 03-08 UTC gap, but they are an older generation of satellites, and don’t have the same resolution that the more modern VIIRS system does. There is a new Metop-SG satellite planned for 2023 that will hopefully provide data from an updated sensor while filling the hourly VIIRS coverage gap.