An electronic system based on long-wavelength infrared (LWIR) sensors is being developed to detect aircraft flying near an upward-aimed, high-power laser beam. In the intended application, the system would alert a human laser operator and/or generate a signal to turn off the laser whenever an aircraft came within a specified exclusion zone - an approximately conical zone, surrounding the laser beam, from which the aircraft must be excluded to protect the human occupants of the aircraft against the laser beam. There could be a potential market for systems like this one in the laser-light-show, free-space laser communication, and lidar industries.
The use of LWIR (in contradistinction to shorter wavelengths) makes it possible to detect the blackbody emission from the skin of an aircraft; it is not necessary to rely on emission from hot engine parts. The system includes two LWIR cameras: a wide-field camera of 18-mm focal length and a narrow-field camera of 75-mm focal length. Both cameras have focal-length/aperture-diameter ratios ("f numbers") of about 1.
The performance of the system was analyzed in tests on observation of several airplanes ranging from a single-engine propeller to full-size commercial multiengine jet transport. In all cases, the system was found capable of detecting and providing alerts for airplanes flying at altitudes between 500 and 11,000 ft (approximately between 0.2 and 3.4 km). In each case, the system provided an alert at least 0.5 second before the aircraft intercepted the laser beam. Inasmuch as the time to close the laser shutter was 0.1 second, the system thus provided a margin of 0.4 second.
This work was done by Keith Wilson, Vachik Garkanian, and Tom Roberts of Caltech and Brian Smithgall of Image Labs International for NASA's Jet Propulsion Laboratory.
NPO-30521
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System Would Detect Aircraft to Turn Off Upward-Aimed Laser
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Overview
The document outlines a technical support package for a system developed by NASA's Jet Propulsion Laboratory (JPL) aimed at detecting aircraft near high-power upward-aimed laser beams. The system utilizes long-wavelength infrared (LWIR) sensors to create a safety mechanism that alerts operators when an aircraft enters a specified exclusion zone surrounding the laser beam. This is crucial for protecting the occupants of the aircraft from potential harm caused by the laser.
The system comprises two LWIR cameras: a wide-field camera with an 18-mm focal length and a narrow-field camera with a 75-mm focal length, both designed to operate effectively in the 7-14 micron range of the electromagnetic spectrum. This wavelength selection allows the system to detect the blackbody emission from the aircraft's skin, rather than relying on the heat from engine parts, making it effective even in challenging conditions such as bright sunlight or moonlight.
Performance tests have demonstrated the system's capability to detect various types of aircraft, including single-engine propeller planes and large commercial jets, at altitudes ranging from 500 to 11,000 feet (approximately 0.2 to 3.4 km). The system provides alerts at least 0.5 seconds before an aircraft intercepts the laser beam, allowing for a safety margin of 0.4 seconds after accounting for the 0.1-second shutter closure time.
The document also discusses the advantages of this LWIR-based system over traditional methods, such as CCD cameras and FAA radar feeds. Unlike these methods, the LWIR system is not affected by ground clutter when aircraft are low to the ground and does not require aircraft to be equipped with transponders. This makes it particularly effective for detecting low-flying aircraft, such as helicopters.
The motivation behind this development is to enhance public safety by preventing high-power laser transmissions from endangering aircraft. The technology has potential applications in various industries, including laser light shows, free-space laser communication, and lidar, highlighting its versatility and importance in ensuring safe operations in environments where lasers are used. Overall, this innovative system represents a significant advancement in aviation safety technology.
