Hydrology « CIMSS Satellite Blog

Large algae bloom in Lake Erie

October 9th, 2011

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

Posted in General interpretation, GOES-15, Google Earth, Hydrology, MODIS | No Comments »

Sediment features in southern Lake Michigan

October 3rd, 2011

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)

Posted in GOES-13, GOES-15, Hydrology, MODIS, Red/Green/Blue (RGB) images | No Comments »

Hydrological impacts of Hurricane Irene

August 29th, 2011

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).