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Home Science Climate How high are the forests? Ask NASA

The U.S. space agency NASA has produced the world's first map of the height of all Earth's forests. The map will help scientists learn more about the carbon cycle and its affect on our atmosphere.

According to the July 19, 2010 NASA media brief 'First Map Of Global Forest Heights Created From NASA Data,' NASA used the following three satellites to generate the map:

(1) NASA's Terra (EOS AM-1, which is part of NASA's Earth Observing System [EOS]),

(2) NASA's Aqua (EOS PM-1, also a component of NASA's EOS, and

(3) Ice, Cloud and land Elevation Satellite (ICESat, a third part of NASA's EOS).

The NASA article states, 'Maps of local and regional forest canopy have been produced before, but the new map is the first that spans the entire globe using one uniform method.'

Dr. Michael Lefsky, from the Department of Forest, Rangeland, and Watershed Stewardship at Colorado State University (Ft. Collins) published a paper in the journal Geophysical Research Letters that summarizes the work performed to produce this one-of-a-kind map. It will appear in the August 2010 issue of the journal.

The images produced by the satellite collaboration found that the world's tallest forests are in the Pacific Northwest (of North America) and in Southeast Asia.

The technology that allowed the map to be produced is called Light Detection and Ranging (LIDAR).

It is a laser system onboard the satellite ICESat that provides 'vertical slices of forest canapy height' by sending pulses of electromagnetic radiation (light) toward Earth, toward its surface and the top of the trees.

Page two continues with more details of the world's forest-height mission by NASA.


The amount of time it takes for the pulses to return to ICESat decides how high the forest is at particular locations. In all, about 250 million laser pulses were used over a 7-year period to produce the map.

Dr. Lefsky states, "Lidar is unparalleled for this type of measurement. It would have taken weeks or more to collect the same amount of data in the field by counting and measuring tree trunks that lidar can capture in seconds."

However, even that enormous number of pulses only collected about 2.4% of the forested area on Earth. The rest of the data was then taken from the moderate resolution imaging spectroradiometer (MODIS) that was on both the Terra and Aqua satellites.

The MODIS instrument is not able to produce the detail as Lidar can, but it is able to produce data on large areas of Earth's surface, without the vertical profile capable of Lidar.

NASA states, 'The new results show that temperate conifer forests -- which are extremely moist and contain massive trees such as Douglas fir, western hemlock, redwoods, and sequoias -- have the tallest canopies, soaring above 131 feet.'

And, 'In contrast, boreal forests dominated by spruce, fir, pine, and larch had canopies typically less than 66 feet. Relatively undisturbed areas in tropical rain forests were about 82 feet tall, roughly the same height as the oak, beeches, and birches of temperate broadleaf forests common in Europe and much of the United States.'

Why is such a map necessary? Does it help us here on Earth?

Read page three for the answer.


NASA says the map is necessary because: 'Measuring canopy height has implications for efforts to estimate the amount of carbon tied up in Earth's forests and for explaining what absorbs 2 billion tons of "missing" carbon each year. Humans release about 7 billion tons of carbon annually, mostly in the form of carbon dioxide. Of that, 3 billion tons end up in the atmosphere and 2 billion tons in the ocean. It's unclear where the remaining 2 billion tons of carbon go, although scientists suspect forests capture and store much of it as biomass through photosynthesis.'

And, 'The new forest height map is a step toward a global map of all above-ground biomass.'

The map is already in the process of being improved.

The Deformation, Ecosystem Structure and Dynamics of Ice (DESDynI) project is scheduled to lift off in 2017 or later.

It is a mission that will study the global environment, specifically it will look at landslides, volcanic eruptions, and earthquakes, and ice sheets, along with studying the changing world climate and its effect on land, species and their habitats, and the carbon cycle.

It will also measure the forests and biomass, which will directly improve the accuracy and detail of the new map of the world's forests.




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William Atkins

William Atkins completed educational degrees in science (bachelor’s in physics and mathematics) from Illinois State University (Normal, United States) and business (master’s in entrepreneurship and bachelor’s in industrial relations) from Western Illinois University






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