May 15th, 2012 | Scott Bachmeier
GOES-15 (left) and GOES-13 (right) 0.63 Âµm visible channel images (click image to play animation)
McIDAS images of GOES-15 (GOES-West) and GOES-13 (GOES-East) 0.63 Âµm visible channel data (above; click image to play animation) revealed the large smoke plume associated with the “Sunflower Fire” that was burning near Payson, Arizona on 15 May 2012. Note toward the end of the animation the appearance of pyrocumulous clouds with overshooting tops over the fire source region. Due to the different satellite viewing angles, the overshooting tops were brightly illuminated on the GOES-15 images, while casting a distinct shadow onto the top of the cloud/smoke plume on the GOES-13 images. Photos of the Sunflower fire from the ground can be seen on the Weather Underground site. Other fires were also burning at that time in Arizona, including the “Gladiator Fire“Â located to the northwest of the Sunflower fire.
The GOES-13 satellite was placed into Rapid Scan Operations (RSO) mode later in the day, providing images as frequently as every 5-10 minutes (compared to the routine 15-minute image interval with GOES-15).
May 15th, 2012 | Scott Lindstrom
GOES-13 enhanced Fog Product (10.7 µm - 3.9 µm)
On the morning of May 14th, a clear morning, the GOES-13 Legacy “Fog Product” that exploits the brightness temperature differences observed by the GOES Imager at 3.9 µm and 10.7 µm, which differences arise because of wavelength-dependent emissivity differences in water clouds, showed fog first on the eastern shores of Lakes Huron and Michigan (at 1015 UTC), and then on the western shores of Lakes Huron and Michigan (at 1401 UTC, and afterwards). These returns occurred despite clear skies.
A similar effect occurred on the morning of May 15th. The image at 1015 UTC showed fog along the eastern side of the Lakes, and the image at 1255 UTC showed fog along the western side of the Lakes. (Note that more widespread mid-level clouds reduced the signal on this day). A POES Fog Product image from 1020 UTC on May 15th (link) did not show the fog signal along the shoreline.
GOES-13 10.7 µm and 3.9 µm channel images (click image to toggle between images)
The image toggle above shows highly magnified imagery over Lake Michigan at 1255 UTC on May 15 2012. There is an apparent 1-pixel shift between the 3.9 µm and the 10.7 µm imagery. If the start element of the image is shifted by 1 infrared pixel, then the toggle between the two images contains no shift. The legacy ‘Fog Product’ is therefore diagnosing fog because the 3.9 µm pixel is over water (cold) and the 10.7 µm pixel is over land (warm). When the 1-pixel shift is rectified, both pixels are either over water, or both over land.
Scientists at NESDIS are working to find the source of this difference.
Update, 17 November 2014
A software fix has been identified and tested. Link.