NASA - National Aeronautics and Space Administration

NASA's Ice, Cloud, and land Elevation Satellite (ICESat) is helping scientists understand how our changing climate is affecting life on Earth with informative 3-D views of polar ice sheets, clouds, mountains, forests and fires. Crisscrossing the globe at nearly 17,000 miles per hour, this space mission is the first to provide vertical measurements of the Earth through the use of an onboard light source.



ICESat First Light Release: Following ICESat.
Click image for animation (18 MB) showing
ICESat collecting elevation data.

Revolutionary Accuracy and Detail

The principal mission of ICESat is to measure the surface elevation of the large ice sheets covering Antarctica and Greenland. Measurements of elevation change over time will show whether ice sheets are melting or growing in association with climate change. The Geoscience Laser Altimeter System (GLAS) on ICESat sends shorts pulses of green and infrared light through the sky 40 times a second, all over the globe, and collects the reflected laser light in a one-meter telescope. This instrument is already providing the most accurate and revealing features of polar ice sheets and is also detecting dust storms, cloud heights and aerosols in the atmosphere, smoke in forest fires and even tree heights.

"NASA has developed tremendous capabilities over the last several decades for observing our Earth in two dimensions. With ICESat, we can see the critical third-dimension (i.e. the vertical) of the land, water, and the atmosphere in new and innovative ways," says Waleed Abdalati, ICESat Program Scientist, NASA Headquarters. "The first few months ICESat data have really been phenomenal. From space, we can see detail in ice and land features that were never visible before."

Left (click image for closer view):: Byrd Glacier, shown in a radar image from RADARSAT-1 (top), is the largest outlet glacier draining ice from the East Antarctic Ice Sheet through the Trans-Antarctic Mountains into the Ross Ice Shelf. The ice sheet is grounded on bedrock and the ice shelf is floating on the ocean. Two ICESat profiles across the glacier show details of the troughs formed on the sides of the glacier as it plows into the ice shelf. The differences between the elevations and widths of the glacier at the inner (red) profile and the outer (black) profile show how the glacier thins and spreads as it merges with the ice shelf. With time, ICESat's measurements of small changes in the elevations of the ice sheets, outlet glaciers, and ice shelves will provide information on whether the rate of ice discharge into the ocean is increasing or decreasing and thus influencing sea level. Credit: NASA

Ice Sheets Provide Climate Change Answers

Are the ice sheets that still blanket the Earth's poles growing or shrinking? Will global sea level rise or fall? In an effort to provide answers to these and other questions about natural and human-induced climate change, scientists are using GLAS data to develop 3-D high-resolution images of ice sheets in areas of Greenland and Antarctica. For the first time, gathering this data will allow scientists to determine whether amounts of ice and snow in the middle of ice sheets are rising or falling, critical in determining future changes in sea level.

ICESat's first look at Antarctic topography has already revealed details such as the ice streams of the Siple Coast and the Amery Ice Shelf, as well the atmospheric phenomena above them.

Right (click image for closer view): Polar Ice Sheets. Credit: NASA

While most small glaciers around the world have been shrinking rapidly and contributing to sea level rise in recent decades, we do not know whether the polar ice sheets are growing or shrinking. Each year about 8 mm (0.3 inches) of water from the entire surface of the oceans goes into the Antarctica and Greenland ice sheets as snowfall. If no ice returned to the oceans, sea level would drop 8 cm (3 inches) every 10 years. Although approximately the same amount of water returns to the ocean in icebergs and from ice melting at the edges, scientists do not know which is greater -- the ice going in or the ice coming out. The difference between the ice input and output is called the mass balance and is important because it causes changes in global sea level. ICESat will help determine how much the ice sheets may be contributing to the present rate of sea level rise of 2 cm (0.8 inches) every 10 years.

Left (click image for closer view): Atmospheric circulation. Credit: NASA

For the future, if climate continues to warm, the polar ice sheets are expected to melt more at the edges due to warmer summer temperatures and grow more in the centers due to increased snowfall. The United Nations Panel on Climate Change has estimated that sea level will rise about 18 inches plus or minus 15 inches over the next century. If the ice sheets melt more than expected, the sea-level rise could therefore be greater. If the ice sheets grow more than expected, future sea level rise could be smaller. By monitoring changes in the melt and growth rates as climate changes in the world's polar regions, ICESat will help reduce uncertainty in these predictions.

The Role of Clouds and Aerosols in Climate Change

The distribution of atmospheric clouds and aerosols (tiny atmospheric particles) is one of the most important factors in global climate. Low clouds typically cool the Earth's surface by reflecting solar radiation while high clouds warm the surface by trapping outgoing radiated heat. Like clouds, aerosols tend to cool the Earth’s surface and heat the atmosphere by scattering and absorbing solar radiation. Thus, for climate studies, especially those interested in determining if the lower atmosphere is warming or cooling, accurate knowledge of aerosols and the type and height of multiple cloud layers in the atmosphere is essential.



Above: ICESat First Light Release: A Continuous View of Clouds.
Click image for Animation (8 MB) showing ICESat collecting cloud data.

For the first time, ICESat is providing scientists with such data, giving researchers the tools to reconstruct the past and project future climate change. Recently, scientists created a 3-D look at the fires in California that will help determine how winds transport smoke and how it mixes with clouds to affect the warming of the atmosphere.

"The amount and coverage of heavy dust and pollution loading in many regions of the Earth that we are seeing in the initial GLAS data are unexpected," said James Spinhirne, principal atmospheric scientist for ICESat at NASA's Goddard Space Flight Center, Greenbelt, Md. These include the rivers of dust from the Sahara desert, which are thought to significantly fertilize the Atlantic and Amazon and are the major source of dust for the southeastern U.S. states, the "Asian Brown Cloud" implicated for climate change, massive dust storms, and large-scale smoke from burning vegetation. The GLAS observations tie the smoke, dust and clouds directly to winds and global transport.

ICESat's Worldwide Uses

Measurements of landscape properties, including elevation, slope, roughness, and vegetation height and density, is a necessary step toward understanding the interplay between formative processes and thus toward more accurate modeling of future changes. Knowledge of these properties and their changes with time is important for resource management, land use, infrastructure, development, navigation, and forecasting the occurrence and impact of natural hazards.

ICESat profiles provide a global sampling of the elevation of the Earth’s land surface with unprecedented accuracy. This globally-consistent grid of elevation data will soon be used as a reference framework to evaluate and improve the accuracy of topographic maps acquired by other airborne and space-based methods such as conventional photogrammetry and radar interferometry.

In addition to acquiring elevation data, ICESat’s GLAS is capable of measuring vegetation cover and enables estimation of above-ground biomass and its loss due to deforestation, an important component of the carbon cycle.

Right (click image for closer view): Forest. As laser pulses from ICESat approach the ground, some of the light is reflected back to the satellite from trees and other vegetation before it reaches the ground. For three laser pulses, the red areas represent the amount of reflected light measured by ICESat from the different heights in trees and from the ground in a Boreal Forest. The shape and strength of the red areas provide information on the height and density of the forest canopy, enabling estimation of the amount of biomass and its variation over the Earth. Credit: NASA

Helping Fulfill NASA's Mission

ICESat was launched January 12, 2003 and is the latest in a series of NASA’s Earth observation spacecraft designed to study the environment of our home planet and how it may be changing. NASA's Earth Science Enterprise (ESE) is dedicated to understanding the Earth as an integrated system and applying Earth System Science to improve prediction of climate, weather, and natural hazards using the unique vantage point of space. Future ICESat missions will extend and improve assessments from the first mission, as well as monitor ongoing changes. Together with other aspects of NASA’s ESE and current and planned satellites, ICESat will allow scientists to better study many aspects of the Earth’s climate.



Above: Click image for animated movie
providing ICESat summary (12 MB).

For more information, please visit:

http://icesat.gsfc.nasa.gov
http://www.gsfc.nasa.gov/topstory/2003/0920icesatfirst.html