Parallax with GOES-R and VIIRS Fire Detection

April 21st, 2022 |
GOES-17 Fire Temperature RGB (upper left) and FDCA Fire Temperature (lower left) and GOES_16 FIre Temperature RGB (upper right) and FDCA Fire Tempeerature (lower right), 1541 – 1946 UTC 20 April 2022 (Click to enlarge)

The Tunnel Fire north of Flagstaff offers an excellent example of why knowledge of Parallax with satellite features is important. In the animations above, note how the location of the warmest pixels are shifted: GOES-17 has the warmest pixels very close to US Highway 89 leading northeast away from Flagstaff; GOES-16 has the warmest pixels just to the west of that road! Which is correct?

Even with surface-based features such as fires, parallax (see other blog posts dealing with parallax here, here, here and here) is an issue with GOES imagery. (Click here to see parallax with lakes) The perceived location is shifted away from the sub-satellite point. So for this example, the true fire location might be somewhere between the satellite-indicated locations. Note also that the FDCA values from GOES-17 differ from those GOES-16; for this fire, GOES-17 values were warmer.

NOAA-20 overflew this fire at 20:50, 20:30 and 20:10 on 19, 20 and 21 April, and imagery from the NASA Worldview site is shown below (Click here for a direct link to the 20 April scene) VIIRS imagery typically has smaller parallax shifts than GOES (and in fact, as detailed here, considerable effort has gone into better georeferencing of VIIRS imagery, as discussed in this blog post and shown in this toggle), and the fire location is therefore more accurate. The 20 April view from NOAA-20 occurred shortly after the end of the animation above, and shows a fire straddling the highway.

NASA Worldview NOAA-20 True Color Imagery and Fire Hot Spots (from I04 3.74 ┬Ám data) on 19, 20 and 21 April 2022 (Click to enlarge)