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LIDAR studies Mt St Helens uplift

08 Nov 2004

NASA and the US Geological survey use LIDAR to monitor the changes in the Mount St Helens volcano.

US scientists are using LIDAR to study the volcano Mount St. Helens which rumbled back to life in September. The technique allows the team from the US Geological Survey and NASA to measure changes in the crater's shape to a vertical accuracy of 10 centimeters.

By comparing the results with LIDAR information from a survey in 2003, the team found that 5.3 million cubic meters of volume change had occurred around the main crater. A new volcanic dome south of the 1980-1986 structure has appeared as well as some new steam and ash vents.

According to NASA, the main crater has now grown to a height of 110 meters and covers an area of 130,000 square meters.

Each LIDAR survey involves packing a scanning laser rangefinder into a small aircraft. NASA has used two similar systems: one from TerraPoint and the second from Sky Mapping, both of the US.

TerraPoint's airborne laser terrain mapping system (ALTMS) uses a diode-pumped Q-switched Nd:vanadate laser emitting at 1064 nm and a repetition rate of 40 kHz. The average density of laser pulses on the ground is 1 per square meter.

"A mission duration is typically 3 to 5 hours," David Harding, a LIDAR specialist from NASA's Goddard Space Flight Center told Optics.org. "The amount of area that can be mapped depends on the complexity of the topography and the length of the flight lines. Anywhere between 30 and 100 square miles can be mapped during a mission."

Harding says that the TerraPoint system will remap the area in mid-November.

Jacqueline Hewett is technology editor on Optics.org and Opto & Laser Europe magazine.

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