<title>Performance comparison of visual, infrared, and ultraviolet sensors for landing aircraft in fog</title>

Abstract

The aviation industry has long sought a means of conducting all weather operations. Presently, airport lighting systems provide the only means for aiding the pilot's transition from instrument to visual acquisition of the runway environment prior to landing the aircraft. The ability for a pilot to see through fog (cloud ceiling and visibility) define the limitations for conducting operations in instrument meteorological conditions. CAT I approaches are authorized down to a runway visual range (RVR) of 2,400 feet, while CAT IIIa approaches are authorized to an RVR of 700 ft. Enhanced vision technologies are being investigated to improve the ability of the pilot to acquire the visual cues (predominantly airport lighting systems) to the runway environment. If enhanced vision enabled the pilot to see 3.5 times farther than the unaided eye, CAT I operations could be conducted under CAT IIIa conditions. This paper examines the relative theoretical and experimental performance of several enhanced vision technologies. This performance analysis compares the runway light detection capability of various infrared sensors with the eye during the dynamics of an aircraft approach and landing. This analysis further compares the IR performance with FogEye, a UV sensor, and a Laser Visual Approach system. The analysis indicates that although the 1.5 micron and 3 to 5 micron IR sensors are capable of improving on the unaided eye, especially in haze and low density fog conditions, only the UV sensor, coupled with relatively minor changes to airport light lenses (to not attenuate UV light), provides the potential to aid the pilot in seeing airport lighting 3.5 times farther than the unaided eye. An 8 to 11 micron IR sensor can support enhanced vision of the actual airport surface. These electro optical capabilities are further compared with the capabilities of Millimeter Wave (MMW) systems. Additional collateral features that would aid in more orderly and safer landing operations are also described.