Early detection of low-flying aircraft in the vicinity of uncontrolled aerodromes is important for nuisance awareness and public safety. Visual and acoustic modalities can be employed to achieve this goal. This paper focuses on the visual aspect, and as such, describes an empirical technique for estimating the visual detection range of a typical low-flying aircraft under clear sky conditions. The figure of merit, R0, establishes the range at first detection, and can be experimentally evaluated from a captured image sequence of an inbound target. Flight tests were conducted at the Smith Falls - Montague airfield in eastern Ontario, Canada. A fully instrumented Convair 580, a twin-turboprop aircraft equipped with a high resolution data acquisition system, was used for the test. Glide-slope inbound approaches and level-flight cloverleaf patterns were flown over the airfield to simulate typical behaviour of low-flying aircraft. The metric R0 is measured from contrast-to-noise ratio curves extracted over individual events, with each curve resulting in a single R0 estimate. Results indicate an average detection range of approximately 8 km for the Convair under clear sky conditions with < 20% broken clouds (sufficiently clear sky). Changing environmental conditions over the course of the event caused significant variability in the observed R0 values computed from individual events.

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