Aug 26 2007
Frontiers in Optics 2007 (FiO), the 91st Annual Meeting of the Optical Society of America, will be held from Sept. 16-20 in San Jose, Calif., alongside Laser Science XXIII, the annual meeting of the American Physical Society Division of Laser Science.
Near-Infrared LIDAR Helps Pilots
Airline pilots will have more advance warning of potentially hazardous atmospheric conditions – such as icing – using a new near-infrared Light Detection and Ranging (LIDAR) system developed by scientists at RL Associates in Chester, Pa. The system, now in a prototype testing phase, will also provide better images in foggy, rainy or extremely hazy conditions, making it easier for pilots to take off and land in those conditions, thereby potentially reducing flight delays.
Right now, other experimental systems use visible green light to detect the different types of particles in the atmosphere. Most commercial planes, however, don't have this kind of system, and flights are grounded rather than risk a foggy landing or misidentifying clouds of icy particles. The RL Associates LIDAR system, which could be quickly commercially deployed, is slated for testing in approximately 18 months.
LIDAR exploits the same basic principle as radar, using light waves instead of radio waves. Lasers use light at wavelengths much smaller than radio waves, so they are much better at detecting very small objects. LIDAR already is frequently used in atmospheric physics – but not on commercial planes – to measure the densities of various particles in the middle and upper atmospheres. According to Mary Ludwig of RL Associates, the system uses a laser light beam that is polarized, or has its electric field pointing in a specific direction. The system beams the polarized infrared light out, and then records the amount of polarization that returns to the sensors. Rain and fog return a less polarized signal, and metal and people return a more polarized signal. The data is then processed to form an image of the ground, or could be translated into verbal commands if needed.
The system can better detect different types of particles in the atmosphere, such as ice, supercooled liquid or just regular water vapor. It can also identify the difference between water vapor and other kinds of substances, such as metal or the human body. Ludwig says the RL Associates system is the first of its kind to use near-infrared. The system also employs a "range-gated detector" that is only turned on for very short periods of time when the return signal is expected. This leads to a vastly improved signal-to-noise ratio, resulting in better images, particularly in obscuring conditions such as fog or haze. (FThG4, "Near-Infrared LIDAR System for Hazard Detection and Mitigation Onboard Aircraft")