Proceedings Article | 15 April 2008
Proc. SPIE. 6957, Enhanced and Synthetic Vision 2008
KEYWORDS: Long wavelength infrared, Thermography, Infrared imaging, Mid-IR, Visible radiation, Fiber optic gyroscopes, Imaging systems, Sensors, Infrared radiation, Mass attenuation coefficient
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.
