During a forest survey, an aircraft-borne lidar sweeps a beam that fires about 70, 000 pulses a second over the canopy.

ECONOMIST: Forest conservation

In 1917 through 1918, owing to the need to ensure the strength and loyalty of its forces, the British registered the Nubians in their survey as occupying a forest area of about 4, 200 acres.

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Dr. VIRGINIA BURKETT (Chief, Forest Ecology Branch, National Wetlands Research Center, U.S. Geological Survey): For example, where we have artificial fill, the subsidence rates are much more rapid than they are on the natural levee deposits.

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