Runway infrared range concept for EVS

Abstract

A major problem in obtaining FAA approval for infrared EVS-based operations under poor-visibility conditions is the lack of correlation between runway visible range and IR attenuation or range. The "IR advantage" in fog, although often substantial, varies greatly as a function of detailed droplet-size distribution. Real-time knowledge of the IR extinction at a given destination is key to reliable operations with lower decision heights. We propose the concept of a Runway Infrared Range (RIRR), to be measured by a ground-based IR transmissometer. Although RVR determination now utilizes single-point scatterometry, the very (Mie) scattering mechanism that often affords a significant IR range advantage necessitates a return to two-point transmissometry. As an adaptation of RVR technology, RIRR will include separate determinations of background-scene and runway/approach lights ranges, respectively. The latter algorithm, known as Allard's Law, will encompass background level, light-settings, visible extinction, and camera performance (usually at short-wave IR). The assumptions and validity of this RIRR parallel those for the traditional RVR. Also, through extended monitoring at a hub, the RIRR may be inexpensively surveyed throughout a fog season, thus predicting the economic benefits of IR-based EVS for that site.