Wildfire in southeastern Montana: a view from 4 different satellites

August 22nd, 2008 |
PS images of MODIS and GOES shortwave IR channels (Animated GIF)

AWIPS images of MODIS and GOES shortwave IR channels (Animated GIF)

Lightning was the cause of a wildfire in southeastern Montana (about 45 miles east-southeast of Miles City) during the afternoon hours on 22 August 2008, which burned a total of about 2600 acres. AWIPS images of the MODIS 3.7 µm and GOES 3.9 µm shortwave IR channels (above) showed a significantly warmer “fire hot spot” on the MODIS 18:20 UTC image (51.0º C, orange pixels) compared to the 18:25 GOES image (36.5º C, dark black pixels). The fire hot spot on GOES imagery did not approach the temperatures seen on the MODIS image until about 20:15 UTC.

This wildfire could be viewed using GOES-11 (GOES-West), GOES-12 (GOES-East), and GOES-13 (undergoing a period of operational testing as “GOES-Central”) — you can see that there was a slight amount of image “wobble”  on the GOES-11 and GOES-12 shortwave IR and visible images, while the corresponding GOES-13 image navigation was very steady (below). Changes to the GOES-13 spacecraft have resulted in improved image navigation compared to the previous GOES satellites.

Also note that the smoke plume on the visible images was much more apparent on the GOES-12 and GOES-13 images — this is due to the fact that the forward scattering angle was more favorable from the viewing perspectives of GOES-12 (positioned at 35º W longitude) and GOES-13 (positioned at 105º W longitude) during the late afternoon hours, which helped to highlight the smoke plume as it drifted southeastward.

GOES-11 + GOES-12 + GOES-13 shortwave IR and visible images (Animated GIF)

GOES-11 + GOES-12 + GOES-13 shortwave IR and visible images (Animated GIF)

A plot of the GOES-11, GOES-12, and GOES-13 3.9 µm shortwave IR brightness temperature values (below) showed a fair amount of variability between the maximum “fire hot spot” temperatures sensed by the different satellites. Although there was general agreement in the trend of increasing temperatures as the wildfire continued to burn, at times the measured IR temperatures differed by as much as 20º K (for example, at 19:45 UTC).  The different satellite viewing angle was a contributing factor to some of these differences — at times the fire was partially obscured by cloudiness that was moving through the region during that period.

GOES-11 / GOES-12 / GOES-13 3.9 µm IR brightness temperatures

GOES-11 / GOES-12 / GOES-13 3.9 µm IR brightness temperatures

Tropical Storm Fay: GOES-13 images during GOES-12 KOZ

August 22nd, 2008 |
GOES-12 and GOES-13 IR images (Animated GIF)

GOES-12 and GOES-13 IR images (Animated GIF)

On the current operational GOES-11 and GOES-12 satellites, data losses occur for several hours each day during the weeks centered around the Spring and Autumn equinox due to (1) Keep-Out Zones (KOZ), and (2) Eclipse. During KOZ, sunlight impinging upon the optical path of the instrument detectors requires the GOES Imager and Sounder to be turned off; during Eclipse, the satellite is in the Earth’s shadow, so the solar panels cannot generate power for the Imager and Sounder instrument packages. On the animation of GOES-12 and GOES-13 10.7 µm IR imagery (above) from 22 August 2008, you can see the period of no data from GOES-12 during such a KOZ — however, data continued to be available using the GOES-13 satellite, due to changes in the spacecraft design that mitigate the KOZ problem.

On AWIPS, data from the GOES-11 (GOES-West) satellite are remapped and used to replace the missing GOES-12 (GOES-East) data during such KOZ and Eclipse periods. During this particular KOZ period, a strong rain band associated with Tropical Storm Fay was moving inland across the Jacksonville, Florida region, creating wind gusts up to 60 mph with heavy rainfall, severe street flooding, and multiple power outages due to downed trees and power lines. On the AWIPS IR images from the KOZ period (below) you can see that the re-mapped GOES-11 data at 05:00 and 06:00 UTC appear somewhat “distorted” due to the large satellite viewing angle (GOES-11 is positioned at 135º W longitude over the Pacific Ocean), and the high-altitude cold cloud top features are shifted significantly eastward due to the associated satellite parallax error.

AWIPS images of GOES IR channel (Animated GIF)

AWIPS images of GOES IR channel (Animated GIF)

The GOES-13 satellite had recently been brought out of on-orbit storage for a period of operational testing. Real-time GOES-13 images are available here and here; GOES-13 sounder derived products are available under the “GOES-Central” heading.