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Longmont, CO 80503

Helicopters over Table Mountain

One of the tactical threats that faces U.S. military personnel and equipment arises from attack helicopters that are masked or hidden by trees, vegetation, and terrain. Such vehicles, though out of the line of sight, produce turbulence in the air above the equipment and terrain. Similarly, military convoys may generate turbulence or "velocity signatures" a few to several tens of feet above and downwind of their location. Coherent Technologies, is developing a remote Doppler wind sensor, or Lidar, to detect such signatures.

Operational field testing was performed over a four day period in early August 2000 above Table Mountain. The primary focus was to measure the atmospheric disturbances generated by an Army helicopter; with particular interest focused on measuring the rotor-blade inflow. This inflow is "visible" for a helicopter which is barely masked by an obstruction. In addition, another CTI system, the CTI WindTracer® 2 Ám commercial lidar system was used for comparison purposes (see photo below). This system is typically used at airports for detecting weather related micro-bursts and aircraft generated wake vortex. The systems performed extremely well and were able to detect helicopter turbulence when the helicopter was completely hidden by the terrain. For more information on what CTI does, go to their website at

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