As covered in the “Problems with Parallax” series, at high latitudes geostationary satellites can experience displacement of features and lower resolution due to parallax. In this addendum, we are comparing the NGFS fire product produced by ABI and VIIRS, which are found on the geostationary GOES-18 and the polar-orbiting NOAA-21 respectively.
This first set of images shows examples of the NGFS product taken by GOES-18 with ABI (left) and by NOAA-21 with VIIRS (right) on June 28, 2026 in the Northwest Territories of Canada. Notice the difference in the NGFS point locations produced using ABI versus VIIRS, as well as the difference in the underlying imagery.
Shortwave Infrared images from GOES-18’s ABI Ch07 (3.90 um) showing areas of high heat in red.
Shortwave Infrared images from NOAA-21’s VIIRS i04 (3.74 um) showing areas of high heat in red.
The GOES-18 ABI DayFire RGB, which shows fires in red; land cover in shades of green and brown; and smoke in grey-cyan.
The NOAA-21 VIIRS DayFire RGB, which shows fires in red; land cover in shades of green and brown; and smoke in grey-cyan.
In the DayFire RGB image comparison below, notice how ABI parallax changes things. The fires get stretched and deformed but because they are near the surface there is little actual displacement, however the elevated smoke is displaced 20-25 miles northward.
The GOES-18 ABI DayFire RGB, which shows fires in red, land cover in shades of green and brown, and smoke in grey-cyan.
The NOAA-21 VIIRS DayFire RGB, which shows fires in red, land cover in shades of green and brown, and smoke in grey-cyan.
So if there isn’t a lot of parallax displacement between ABI and VIIRS with fires at the surface, why are the ABI NGFS points so far away from the VIIRS NGFS points? The reason is pixel size. An NGFS point is located at the center point of a pixel and since ABI pixels are so large and stretched, the center points and resulting NGFS points are displaced as well.
Location differences due to parallax displacement are easier to correct than those caused by pixel shape. Parallax displacement can be corrected if the height of the feature can be estimated, however there is no sub-pixel information to locate a point somewhere other than the pixel’s center point.
By Carl Dierking & Grace Veenstra