Concord, NH - New airborne technology known as light detection and ranging (LiDAR) is being used to accurately map land surface elevations across more than half of New Hampshire, from Massachusetts to Quebec. This major data collection project represents a partnership between the State of New Hampshire, US Geological Survey (USGS), USDA Natural Resources Conservation Service, Federal Emergency Management Agency, and the White Mountain National Forest. The project footprint adjoins several areas of the state where LiDAR data already exist with an additional 5,200 square miles along the Connecticut River and around Lake Winnipesaukee. As a result of this project, enhanced elevation data is now available for more than 80 percent of the state, bringing the USGS 3D Elevation Program Initiative closer to achieving its ambitious goal of mapping the entire country in 8 years.

Accurate, high-resolution data on land surface elevations and contours (topography) are critical for mapping the extent of areas impacted by river flooding as well as numerous other economic development and natural resource applications. Before LiDAR, topographic maps produced decades ago by the USGS were the most commonly used source of elevation data for engineers and other resource professionals. However, at best, the elevation contour lines on these maps have a vertical accuracy of +/- 5 feet for much of the state and +/- 20 feet in more mountainous areas, too inaccurate to support modern computerized mapping methods. LiDAR technology has been proven to provide a vertical accuracy of +/- 6 inches, and has become the widely accepted standard for acquiring elevation data over large geographic areas.

The mapping is performed using a rapidly pulsing laser that is directed toward the ground from an airplane flying 180 miles per hour in a straight line at an altitude of over a mile. As the laser sweeps back and forth along the flight path, a highly sensitive detector measures exactly how long it takes for each beam of light to travel to the ground and reflect back to the plane. One half of the round-trip travel time is then converted into a distance based on the speed of light, resulting in millions of closely spaced ground elevation data points. Data are collected along parallel, overlapping flight lines to achieve complete coverage, much like mowing the lawn.

Because LiDAR can "see" the ground even when it is covered by trees, the method is ideal for mapping in heavily forested areas like much of New Hampshire. Details as subtle as old stone walls and cellar holes are readily recorded. The collection of the data was just completed. Once the data has been reviewed for quality assurance, the final elevation data for the entire project area will be publically available by late summer or early fall 2016.


Posted 11/25/15