Abstract
A new laser signal for communicating with aircraft is being developed to warn aircraft against entering metropolitan area air defense identification zones. The purpose of this experiment was to determine the irradiance and laser characteristics (color and frequency) of effective warning signals in simulated day and night scenes. Ten subjects, half of whom had flight experience, viewed six types of laser exposures (3-Hz and 10-Hz green beams, 3-Hz and 10-Hz red beams, and red and green beams alternating at 3 Hz and 10 Hz) superimposed on either a day or night scene. Laser irradiances varied over a 5.25 log unit range for each condition and over an irradiance range of over 2.2e-11 W·cm−2 to 2.0e-5 W·cm−2. While performing a concurrent visual tracking task, subjects were required to decide whether each laser beam presented to them was an effective warning signal. RMS error was measured on the tracking task to evaluate disruptive irradiance endpoints. The results showed that, for night scene conditions, laser exposures at approximately 4.0e-8 W·cm−2 were rated as a 50% probability of warning. For the simulated day scene, irradiances of more than 7.0e-8 W·cm−2 were required. A 90% probability of warning was achieved at irradiance levels of 8.0e-7 W·cm−2 at night and 1.5e-6 W·cm−2 for a simulated day scene. Red-green alternating exposures were more likely to be rated as warning signals than red only or green only exposures. While all the subjects exhibited similarly shaped functions, the variability between subjects for a 50% probability of warning varied over about 2.5 log units. Flicker rates of 10-Hz were a little more effective than rates of 3-Hz as warning signals. Specific disruption on the tracking task due to the laser exposures occurred above 4.0e-6 W·cm−2 and 1.0e-6 W·cm−2 in the day and night conditions, respectively. These results suggest the characteristics of a laser signal required to convey warning in flight and the results should be scalable to normal daytime irradiances.
Research supported by Air Force Research Laboratory, Optical Radiation Branch