CIMSS Satellite Blog

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)

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

There are a number of satellite signatures that denote areas of potential turbulence, and AWIPS images of the GOES-12 10.7 µm IR channel on 27 July 2008 (above) displayed two of the more common indicators: rapidly developing convection, and transverse banding. A decaying mesoscale convective system was moving southeastward across Minnesota and Iowa, with pulses of new convection developing rapidly over northern Iowa — one pilot reported a severe updraft that caused a rapid increase in altitude of 2000 feet as the aircraft was flying over the Minnesota/Iowa border region.

Along the periphery of the northeastern quadrant of the decaying MCS, a well-defined area of “transverse banding” formed (the narrow cloud band features were generally perpendicular to the mean wind direction aloft) –  there were a few reports of turbulence that appeared to be associated with this transverse banding feature: over Lake Michigan around 17:30 UTC,  over northeastern Wisconsin around 19:20 UTC, and over western Lower Michigan around 20:09 UTC.

The transverse banding features that were seen on the 4-km resolution GOES IR imagery were even more obvious on an AWIPS image of the 1-km resolution MODIS 11.0 µm IR channel (above), and also on a comparison of 250-m resolution MODIS true color images from the SSEC MODIS Today site (below).

Since we’re on the topic of potential aviation hazards, also note the hazy features that were evident on the MODIS true color images (just to the east of the transverse banding) — these hazy features were due to the presence of thick smoke from wildfires that had been burning over parts of northern Saskatchewan, Canada for several days (see the US Air Quality “Smog Blog” for details).  GOES-12 visible imagery indicated that this smoke began moving southeastward across Manitoba and into the north-central US on 25 July (QuickTime animation). The smoke was likely confined to layers aloft, but aircraft flying through those smoke layers would encounter significantly reduced visibilities at those altitudes. An AWIPS image of the 1-km resolution MODIS 3.7 µm IR channel (below) showed a large number of fire “hot spot” signatures across far northern Saskatchewan at 04:05 UTC (10:05 PM the previous evening, local time).

Many large wildfires continued to burn in parts of California on 08 July 2008. A comparison of MODIS false color and true color images from the SSEC MODIS Today site (above) demonstrated the use of the false color imagery for determining the areal coverage of burn scars in the Los Padres National Forest south of Monterey, California; the burn scars show up as reddish-brown features, with active fire hot spots having a brighter light pink appearance on the false color imagery. In the true color imagery, it is difficult to discriminate between thick smoke from the fires and stratus clouds right along the coast, but the smoke exhibits a light blue tint on the false color imagery.