University of Wisconsin-Madison Space Science and Engineering Center

CIMSS Satellite Blog

Drifting ice field in Green Bay

March 11th, 2009

GOES-13 visible images

Strong northwesterly winds (gusting as high as 70 mph at Grand Marais in the Upper Peninsula of Michigan, and 57 mph at Washington Island in northeastern Wisconsin) caused a large portion of the land-fast ice in the far northern portion of Green Bay to break away and begin drifting eastward toward Lake Michigan on 11 March 2009. Once the clouds cleared over that region, GOES-13 visible images (above) showed the large ice feature as it moved slowly eastward.

According to the CIMSS Mesoscale Winds product (below), the speed of the ice field drift was in the 15-25 knot range. These wind vectors were generated by tracking targets on 3 consecutive GOES-12 visible images.

GOES-12 visible image + CIMSS mesoscale winds

A false-color Red/Green/Blue (RGB) composite made using AWIPS images of the MODIS visible and the 2.1 µm “Snow/ice” channels (below) confirmed that this was indeed an ice feature — snow and ice are strong absorbers at the 2.1 µm wavelength, making snow cover (and especially ice features) exhibit a darker red appearance on the false-color imagery. In contrast, the supercooled water droplet clouds appear as cyan to brighter white colored features. The ability to create these types of RGB images should be a new feature available on future releases of AWIPS-2.

MODIS false color image (using Visible and Snow/ice channels)

250-meter resolution “true color” and “false color” images from the SSEC MODIS Today site (below) showed better detail of the ice field structure. Also note the long, narrow southwest-to-northeast oriented tornado damage path (from the 07 June 2007 tornado event), located about 30 miles (48 km) inland to the west of Green Bay.

MODIS 250-m true color and false color images

MODIS 250-m resolution "true color" and "false color" images

Posted in GOES-12, GOES-13, Marine weather, MODIS, Red/Green/Blue (RGB) images, Satellite winds, Winter weather | Comments Off

Mountain wave signatures on water vapor imagery

March 9th, 2009

Composite of GOES-11 (GOES-West) + GOES-12 (GOES-East) water vapor imagery

Strong winds over much of the southwestern US (surface winds gusted to 75 mph at Sierra Rotors Site 7 in California) were responsible for producing large areas of mountain waves across a good deal of that particular region on 09 March 2009. These mountain waves were seen on AWIPS composite images of the 8-km resolution GOES-11 (GOES-West) 6.7 µm and the 4-km resolution GOES-12 (GOES-East) 6.5 µm water vapor channels (above) — and there were a number of pilot reports of light to moderate turbulence within the 26,000-50,000 feet layer over the southwestern US.

MODIS + GOES-11 water vapor imagery

A comparison of the 1-km resolution MODIS 6.7 µm with the 8-km resolution GOES-11 water vapor imagery at around 18:30 UTC (above) showed a marked improvement in the ability to detect the location and areal coverage of the mountain waves.

MODIS + GOES-11/GOES-12 water vapor imagery

A similar comparison of the the 1-km resolution MODIS 6.7 µm with a composite of the 8-km resolution GOES-11 6.7 µm (GOES-West) plus the 4-km resolution GOES-12 6.5 µm (GOES-East) water vapor images (above) demonstrated the improvement in mountain wave detection capability with the newer 4-km water vapor channel on the newer GOES-12 (and also the GOES-13) satellites — but as expected, neither are as capable as the 1-km MODIS water vapor channel in terms of displaying mountain wave signatures.

GOES-13 water vapor images

GOES-13 shares the same 4-km resolution 6.5 µm water vapor channel as GOES-12, but in this case GOES-13 had the advantage of a more direct satellite view angle (GOES-13 is positioned over the Equator at 105º W longitude). As a result, the GOES-13 water vapor imagery (above) did a very good job of depicting the areal coverage (as well as the temporal evolution) of the mountain wave signatures. Note how some wave signatures were stationary (anchored to the terrain that caused them to form), while other wave signatures appeared to propagate downwind over time.

Posted in Aviation, GOES-11, GOES-12, GOES-13, MODIS | Comments Off

The Moon on GOES-13 imagery

March 9th, 2009

GOES-13 visible and 10.7 µm IR images at 17:45 UTC (left) and 18:15 UTC (right)

Several times a year the Earth’s Moon is captured on geostationary satellite imagery — but the geometry has to be exactly right in order for the Moon to be seen. A comparison of GOES-13 images (above) shows the Moon at two different times on 09 March 2009 – first at 17:45 UTC (left image panels) with an apparent location to the northwest of Alaska, and again 30 minutes later at 18:15 UTC (right image panels) with an apparent location to the northeast of Greenland.

Since much of the Moon was illuminated by the Sun, the surface exhibited a hot IR brightness temperature (around 331º K / 58º C / 157º F) as indicated by the bright yellow color enhancement on the IR images. The yellow/black striping on the IR images is due to the fact that the very hot lunar surface temperatures highlight the detector-to-detector responsivity differences. Also note that the shape of the moon was not round in the images, but somewhat “oblong” — this is due to the fact that while the Moon is moving fairly quickly across the satellite field of view, the relatively slow horizontal scanning direction of the GOES imager instrument makes the shape of the Moon appear a bit distorted.

The GOES-13 visible image of the Moon (below, courtesy of Tim Schmit, NOAA/NESDIS/STAR/ASPB) was acquired during the initial GOES-13 post-launch testing during the Summer of 2006. One of the test procedures addressed lunar calibration: the goal was to observe the Moon as soon as possible after launch of GOES-13, in order to establish a baseline for future study of GOES instrument degradation.