MODIS true color and false color images

A previous blog post discussed the sediment features seen in southern Lake Michigan in early October of 2011. However, looking a bit farther to the east over Lake Erie several days later, a 09 October 2011 comparison of 250-meter resolution MODIS true color and false color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above) showed a notable contrast between the two lakes: large green colored features covered much of western Lake Erie, compared to the cyan colored sediment that was seen in southern Lake Michigan (as well as southern Lake Huron).

According to the NASA Earth Observatory site, this is one of the worst algae blooms in Lake Erie in decades, brought about in part due to large amounts of runoff into the lake following a period of above-normal precipitation. The thickest portions of the algae bloom appear brighter green in the false color images, similar to the way that dense vegetation does.

A comparison of the consecutive Terra (16:52 UTC) and Aqua (18:33 UTC) MODIS true color images (below, viewed using Google Earth) seemed to suggest a slight northward movement of the algae features during the 91 minutes between the two images.

Terra (16:52 UTC) and Aqua (18:33 UTC) MODIS true color images

An animation of GOES-15 0.63 µm visible channel images (below) confirmed the gradual northward movement to the algae bloom features over western Lake Erie during the day. Surface winds were generally light out of the south across the region, so most of this motion was likely driven by lake currents.

GOES-15 0.63 µm visible channel images

MODIS true color images: 02 October (left) and 03 October (right)

As was highlighted in news stories posted by the National Weather Service forecast offices at Chicago and Milwaukee, a large amount of sediment was seen in southern Lake Michigan following a strong wind event which produced very large waves. A comparison of 250-meter resolution MODIS true color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above) showed one particularly large sediment feature protruding northward from the southeastern part of Lake Michigan on 02 October and 03 October 2011.

A comparison of AWIPS images of 1-km resolution MODIS 0.65 µm visible channel data with the corresponding 1-km resolution MODIS Sea Surface Temperature (SST) product on 03 October (below) showed that while the prominent sediment feature was embedded within a larger scale area of warmer waters (SST values in the lower 60s F, darker red color enhancement) in the far southern part of the lake, there was not necessarily a 1:1 correspondence between the sediment pattern and the sea surface temperature pattern.

MODIS 0.65 µm visible channel image + MODIS Sea Surface Temperature product

GOES-13 0.63 µm visible channel imagery (below; click image to play animation) indicated that the prominent sediment feature was moving slowly northward early in the day on 03 October — however, once the northwesterly winds reported by the mid-lake buoy began to increase and gust to 16 knots later in the day, the northward motion of the sediment feature appeared to slow somewhat.

GOES-13 0.63 µm visible channel images (click image to play animation)

===== 06 October Update =====

A sequence of daily 250-meter resolution MODIS true color RGB images from 02, 03, 04, 05, and 06 October (below) show the changes in shape and location of the large sediment feature in the southeastern part of Lake Michigan.

MODIS true color images from 02, 03, 04, 05, and 06 October

In addition, daily 15-minute interval GOES-15 0.63 µm visible channel images from that same period (below; click image to play 5-day animation) further show how the sediment patterns were transported and morphed by the Lake Michigan water currents.

GOES-15 0.63 µm visible channel images (click image to play 5-day animation)

MODIS true color images: 16 August and 28 August 2011

Heavy rainfall associated with Hurricane Irene included 20.40 inches at Virginia beach, Virginia and 20.00 inches at Jacksonville, North Carolina (HPC summary). Winds gusted as high as 115 mph at Cedar Island, North Carolina. The effects of the heavy rain and strong winds can be seen in a before/after comparison of 250-meter resolution MODIS true color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above). On the “before” image (16 August 2011), there was a large smoke plume seen from a fire that was burning in the Great Dismal Swamp area in far southeastern Virginia; on the “after” image (28 August 2011), water turbidity was significantly enhanced due to suspended sediment across the Outer Banks region of North Carolina — and a narrow filament of sediment was being actually being entrained into the flow of the Gulf Stream.

AWIPS images of the corresponding MODIS 0.65 µm visible channel data and the MODIS Sea Surface Temperature (SST) product (below) showed that the enhanced turbidity features seen on the MODIS true color image generally exhibited slightly cooler SST values (in the middle to upper 70s F, blue color enhancement) compares to the waters located closer to the Gulf Stream (SST values in the lower 80s F, darker red color enhancement).

MODIS 0.65 µm visible channel image + MODIS Sea Surface Temperature image

Farther to the north, another before/after MODIS true color image comparison revealed additional areas of sediment being carried off the coast of the Northeast US (below). Also note that there was a great deal of sediment in the Hudson River (perhaps better seen in this 20 August / 29 August comparison).

MODIS true color images: 26 August and 29 August 2011

MODIS 0.65 µm visible channel image + MODIS 2.1 µm near-IR "snow/ice channel" image

AWIPS images of MODIS 0.65 µm visible channel data and MODIS 2.1 µm near-IR “snow/ice channel” data (above) demonstrated the utility of the snow/ice channel imagery for highlighting the areal extent of flooding along parts of the lower Mississippi River on 17 May 2011. Water is a strong absorber at the 2.1 µm wavelength, so it appears very dark on the MODIS snow/ice channel image.

CIMSS participation in GOES-R Proving Ground activities includes making MODIS imagery available for National Weather Service forecasters to add to their AWIPS workstations. The VISIT training lesson “MODIS Products in AWIPS” is also available to help users understand the products and their applications to weather analysis and forecasting.

A closer view using 250-meter resolution MODIS true color (using channels 1/4/3) and false color (using channels 7/2/1) MODIS Red/Green/Blue (RGB) images from the SSEC MODIS Today site (below) revealed the darker brown “muddy” appearance of much of the flooded areas adjacent to the Mississippi River, due to high sediment loading of the water. Water exhibited a very dark blue appearance on the MODIS false color image.

250-m resolution MODIS true color and false color Red/Green/Blue (RGB) images

MODIS 0.65 µm visible channel image + MODIS 2.1 µm near-IR "snow/ice channel" image

A comparison of AWIPS images of the 1-km resolution MODIS 0.65 µm visible channel (first shown with a map overlay and location of METAR sites) and the corresponding 1-km resolution MODIS 2.1 µm near-IR “snow/ice channel” (above) shows the areal coverage of flood waters across the region of the confluence of the Mississippi River and the Ohio River on 04 May 2011. Since water happens to be a strong absorber at the 2.1 µm wavelength, it shows up as a very dark feature on the MODIS “snow/ice channel” image — making it more useful for locating areas of flooding than just a simple visible channel image.

A similar near-IR channel will be on the ABI instrument of the future GOES-R satellite. CIMSS participation in GOES-R Proving Ground activities includes making a variety of MODIS images and products available for National Weather Service offices to add to their local AWIPS workstations.

MODIS True-color imagery from the SSEC MODIS Today website can be used to compare data from this year and last year, shown below. In the linked-to-images, the Mississippi River north of Memphis (located at the bottom edge of each image) meanders through the center part of the images. There are several former meanders of the river in Arkansas and Tennessee that are filled with water this year, but not last.

MODIS true color images (04 May 2010 and 04 May 2011)

MODIS false color image comparison between 11 April and 24 April 2011

A comparison of MODIS false color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above) shows the increase in areal coverage of flooding along the Red River of the North, from north of Grand Forks, North Dakota into southern Manitoba. Also evident is the melting of most of the snow cover across northeastern North Dakota, and the melting of portions of Devils Lake (snow and ice appear as cyan features on the false color images, while water has a darker blue appearance).

MODIS false color RGB image (displayed using Google Earth)

A MODIS false color Red/Green/Blue (RGB) image from the SSEC MODIS Today site (above; courtesy of Kathy Strabala, CIMSS) showed the areal extent of the unprecedented overland flooding that was occurring along parts of the Red River in North Dakota on 11 April 2011. Spring snow-melt along with recent heavy rainfall were contributing to the flooding. Interstate 29 north of Fargo was closed on the previous day due to rising floodwater covering the roadway.

AWIPS images of 1-km resolution MODIS 0.65 µm visible channel and 2.1 µm near-IR “snow/ice” channel data (below) was also useful for helping to highlight the location of the flooded areas. Both water and frozen lakes appear as very dark features on the 2.1 µm “snow/ice” channel image — but the frozen lakes are brighter white on the visible image.

MODIS 0.65 µm visible image + MODIS 2.1 µm near-IR "snow/ice" image

A comparison of 250-meter resolution MODIS true color and false color RGB images (below) offered a more detailed view of the flooding in the Fargo and Grand Forks areas. The flooded areas exhibited a “muddy” light brown appearance on the true color image. Farther to the west, the still-frozen Devils Lake (whose water level had reached a new record high level) and portions of northeastern North Dakota that still had snow cover (as much as 6 inches remaining on the ground) could also be seen (snow cover and frozen lakes appeared as lighter blue to cyan features on the false color image).

250-meter resolution MODIS true color and false color RGB images

MODIS false color images (13 September and 29 September 2010)

A comparison of 250-meter resolution MODIS false color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above) show dramatic changes in some of the larger rivers (primarily the Mississippi River and the Wisconsin River) before (13 September 2010) and after (29 September 2010) parts of the Upper Midwest region received very heavy rainfall. Two locations in Wisconsin are highlighted where there were evacuations ordered due to flooding: Arcadia (on 23 September) and Portage (on 27 September).

These false color Red/Green/Blue images are created using MODIS bands 7/2/1 — water shows as the very dark features, allowing the changes in river boundaries  (as well as areas that have experienced significant water inundation) to be easily seen.

MODIS visible, 11.0 µm IR, and Land Surface Temperature images

A late-season winter storm dumped as much as 29.0 inches of snow across parts of the Upper Peninsula of Michigan during the 19-21 April 2009 period — in fact, the 20.5 inches that fell at Marquette was their 3rd largest late season 2-day snowfall on record. AWIPS images of the MODIS visible channel, 11.0 µm IR window channel, and the Land Surface Temperature (LST) product (above) showed that a few areas of snow cover still remained on 28 April 2009. MODIS IR brightness temperatures were as cold as +2º to +5º C (darker blue colors) over the patches of snow cover, which still appeared as varying shades of white on the visible image. While there were some MODIS Land Surface Temperature values as cold as the middle 40s F (darker green colors) over the patches of snow cover, the coldest areas showed up as black “NO DATA” pixels in the LST product, due to the product algorithm mistakenly identifying the sharp temperature gradients as cloud features.

Unfortunately, there were no National Weather Service Cooperative Observer locations in the region that reported any snow depth on the morning of 28 April, so the true depth of the remaining snow cover was not known — however, according to an email reply from meteorologist  John Dee (who lives on the Keweenaw Peninsula):

The snow that remains is from the season and is quite variable in depth, with shaded areas in the higher terrain still having a foot or a bit more, but unshaded areas being bare and those that catch some sun and some shade having anywhere in between zero and a foot. I’d say probably 2-6″ still remaining if you took the bare with the other areas with varying depth and averaged things out.

AWIPS examples of a 250-meter resolution MODIS true color image and a 1-kilometer resolution MODIS Sea Surface Temperature (SST) product (below) showed two items of interest: (1) there was a good signal of the runoff of snow-melt water as it flowed northward from the Ontonagon River basin into Lake Superior (note the reddish hue of the water immediately offshore, due to the iron-rich sediment), and (2) the water temperatures in Lake Superior were still quite cold, with MODIS SST values generally in the 35º to 38º F range (darker blue colors).

MODIS true color image + MODIS Sea Surface Temperature

GOES-12 IR imagery (Animated GIF)

After passing over Key West on 18 August, Tropical Storm Fay made landfall along the Gulf Coast of the Florida peninsula on 19 August 2008. GOES-12 IR imagery from the CIMSS Tropical Cyclones site (above) showed that Fay was moving slowly northward toward a weakness in the deep layer mean flow. GOES-12 IR cloud top temperatures continued to cool as Fay moved inland (IR brightness temperatures near the Florida coast were as cold as -81º C at 08:40 and 09:15 UTC), with an AWIPS image of the MODIS 11.0 µm IR channel (below) showing an eye structure at 16:10 UTC.

AWIPS MODIS IR image

The appearance of the eye structure continued to improve on GOES-12 visible imagery (below) even as Fay remained over land during the day, and QuikSCAT winds indicated that tropical storm force winds extended out across the adjacent offshore waters of both the Gulf of Mexico and the Atlantic Ocean.

GOES-12 visible image + QuikSCAT winds

The GOES-12 satellite was placed into Rapid Scan Operations (RSO), allowing images at 5-10 minute intervals (below) as the center of Fay grazed Lake Okeechobee in southern Florida. Winds gusted to 78 mph at Moore Haven along the western shore of Lake Okeechobee (MODIS image in Google Earth). It is interesting to note that MODIS Sea Surface Temperatures in Lake Okeechobee on Sunday 17 August were as warm as 91.8 F — this large body of warm water may have acted as an additional source of  evaporation and sensible heat to help fuel convection around the eye of Fay.

Note that Fay almost seemed to exhibit a slight amount of trochoidal oscillation on the GOES-12 images (though nothing like that seen with Hurricane Wilma back in 2005). However, a comparison of GOES-12 and GOES-13 RSO visible images revealed that this apparent “eye wobble” was due to irregularities in satellite navigation (the image-to-image navigation is significantly improved on the newer GOES-13 satellite, due to changes in the spacecraft design).

GOES-12 RSO visible images (Animated GIF)

Due to the aforementioned weak deep layer mean flow regime, the future motion of Fay was very uncertain, as could be seen by the large spread of model forecast tracks (below).

GOES-12 water vapor imagery + model forecast tracks

Even though Fay was not a particularly strong tropical cyclone, the slow forward motion meant an increased threat for heavy rainfall over the southeastern US; the Hydrometeorological Prediction Center 5-day total  precipitation accumulation forecast (below) suggested that rainfall could approach 15-20 inches in parts of Florida and Georgia.

HPC 5-day total precipitation accumulation forecast

** 29 AUGUST UPDATE **

The Melbourne, Florida NWS office received a storm total of 19.62 inches of rain, with  an amazing 27.65 inches reported 8 miles northwest of Melbourne (below).

Total rainfall from Fay (courtesy of NOAA HPC)