NASA Terra MODIS Image captures Great Lakes in the Fall

A few days after autumn showed up on the calendar in the Northern Hemisphere, it showed up on the landscape of North America. 

Image Credit: Jeff Schmaltz at NASA GSFC. Caption by Mike Carlowicz

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this view of fall colors around the Great Lakes on Sept. 26, 2014.

The changing of leaf colour in temperate forests involves several causes and reactions, but the dominant factors are sunlight and heat.

Since temperatures tend to drop sooner and sunlight fades faster at higher latitudes, the progression of fall colour changes tends to move from north to south across North America from mid-September through mid-November.

In late summer and autumn, tree and plant leaves produce less chlorophyll, the green pigment that harvests sunlight for plants to convert water and carbon dioxide into sugars.

The subsidence of chlorophyll allows other chemical compounds in the leaves, particularly carotenoids and flavonoids, to emerge from the green shadow of summer.

These compounds do not decay as fast as chlorophyll, so they shine through in yellows, oranges, and reds as the green fades.

Another set of chemicals, anthocyanins, are associated with the storage of sugars and give the leaves of some species deep purple and red hues.

NASA MODIS Image: US Great Lakes Frozen

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite captured this image on Feb. 19, 2014. 

Credit: NASA

A deep freeze has settled in over the Great Lakes this winter and a new image released by NASA shows the astonishing extent of the ice cover as seen from space.

NASA's Aqua satellite captured this image of the lakes on the early afternoon of Feb. 19, 2014.

At the time, 80.3 percent of the five lakes were covered in ice, according to the Great Lakes Environmental Research Laboratory (GLERL), part of the National Oceanic and Atmospheric Administration (NOAA).

Earlier this month, ice cover over the Great Lakes hit 88 percent for the first time since 1994.

Typically at its peak, the average ice cover is just over 50 percent, and it only occasionally passes 80 percent, according to NASA's Earth Observatory.

A false colour image of the frigid Great Lakes on Feb. 19, 2014. 

Credit: NASA

Cold temperatures that have persisted in the region are largely responsible for this year's thick layer of ice, but cryospheric scientist Nathan Kurtz, of NASA's Goddard Space Flight Center, told the Earth Observatory that "secondary factors like clouds, snow and wind also play a role."

And some lakes are more frozen than others.

Nathan Kurtz

While the ice cover over Lake Erie, Lake Superior and Lake Huron is approaching 100 percent, Lake Ontario is only around 20 percent frozen and Lake Michigan is about 60 percent covered, according to the latest update from GLERL.

NASA researchers also put together a false-colour image combining shortwave infrared, near infrared and red wavelengths to pick out ice from other elements that look white in visible-wavelength images like snow, water and clouds. In this image, ice appears pale blue, and the thicker it is the brighter it looks.

Open water, meanwhile, is shown in navy, snow is blue-green and clouds appear either white or blue-green, according the Earth Observatory.

NASA and NOAA help reveal melt secrets of Great Lakes ice

A colour-coded image of major ice types on Lake Superior, made from a RADARSAT1 radar backscatter image using a new NASA and NOAA-developed technique. 

Credit: NOAA Great Lakes Environmental Research Laboratory and NASA/JPL-Caltech

Two scientists from NASA and NOAA have developed a new space-based technique for monitoring the ice cover of the Great Lakes that is so accurate it can identify a narrow channel of open water cut through the ice by an icebreaker—even at night.

"In the dark, it's difficult to read a map that's right in front of you," said Son Nghiem of NASA's Jet Propulsion Laboratory, Pasadena, Calif., one of the developers of the new technique.

Son Nghiem

"Yet we now have a way to use satellite radars almost 500 miles [800 kilometers] out in space to see through clouds and darkness and map ice across the Great Lakes."

Ice on the Great Lakes puts a big chill on the U.S. and Canadian economies, affecting shipping, fishing and also public safety when winter and spring flooding are caused by ice jams.

It has a significant impact on the regional environment and ecological systems as well. Yet previous techniques of analyzing satellite observations of the ice sometimes misidentified ice as water and vice versa.

The new method, co-developed by Nghiem and his colleague George Leshkevich of NOAA's Great Lakes Environmental Research Laboratory, Ann Arbor, Mich., not only corrects that problem, it also gives a more accurate analysis of ice characteristics, such as whether the ice is dense or full of bubbles, and whether it has melted and refrozen.

Leshkevich said the method has now been transitioned to NOAA for routine use in generating ice maps across the Great Lakes.

"These maps will provide important information for environmental management, ice forecasting and modeling, off-shore wind farm development, operational icebreaking activities in support of winter navigation, and science research."

The more accurate classification of ice will also be useful for scientific research into such questions as how the Great Lakes are responding to, and leading, climate change in the upper Midwest.

More information: www.iaglr.org/jglr/release/39/2013.05.003_leshkevich.php