Aerospace and Electronic Systems Magazine September 2016 - 10

Prototype Sense and Avoid System Onboard a ScanEagle Unmanned Aircraft

Figure 4.

A map showing danger area D651, which is centred on the Watts
Bridge airfield. The border of D651 is shown by the red dashed line.
Four example ASL approach paths are also shown (white lines). The
3 nmi labels show the distances of the ASL's starting positions from
the midpoint of the flight path (red dots). The starting positions of the
ScanEagle are also shown (white circles).

search Centre for Aerospace Automation (ARCAA), which is part
of the Queensland University of Technology (QUT).
A number of the Cessna 172R's key specifications are shown
in Table 1. The Cessna is a common general aviation (GA) aircraft
and, as such, represents a typical aircraft that you might encounter
in class G airspace. Thus, the ASL is a good candidate to use as a
threat aircraft for testing the SAA system.

WATTS BRIDGE MEMORIAL AIRFIELD
The SAA FT&E campaign was carried out at Watts Bridge Memorial Airfield, Queensland, Australia (27° 05' 54"S, 152° 27' 36"E).
Watts Bridge is approximately 38 nmi northwest of Brisbane, the
state's capital. This nontowered aerodrome has three grass runways: two parallel runways and one cross strip.
The ScanEagle was operated within danger area D651, which
is shown in Figure 4. The danger area is centred on Watts Bridge
airfield and extends from the surface to 3000 ft above mean sea
level (AMSL). A danger area is an airspace of defined dimensions
within or over which activities of potential danger to aircraft flying
over the area may exist [19]. Aircraft are not excluded from danger
areas and the airfield was open during the SAA FT&E campaign.
All flight tests were conducted in nonsegregated3 Class G airspace. Figure 4 shows four examples of the ASL's flight paths. For
each test the ASL started its approach from outside the danger area
and flew over the top of D651 towards the flight path's midpoint.
The ScanEagle started its approach from within the danger area.
The ScanEagle headed towards the same midpoint as the ASL, but
from the opposite direction.
An airspace coordinator was located on the airfield during the
FT&E campaign. The airspace coordinator kept a radio and visual
"watch" in order to coordinate the SAA experiments with other
aircraft traffic in the vicinity of the airfield.
3

Segregated airspace: Airspace of specified dimensions allocated for exclusive use to a specific user(s) [38].

Figure 5.

An example image from the SAA system, which shows the threat aircraft, a Cessna 172, at a range of 1 km (5 mm lens configuration). The
inset shows a magnified view of the highlighted area.

FLIGHT TEST AND EVALUATION RESULTS
OVERVIEW
The prototype SAA system was integrated onboard the ScanEagle
and successfully flown in an FT&E campaign that consisted of
four separate ScanEagle flights in nonsegregated civilian airspace
in December 2013. The ASL and ScanEagle performed 22 headon collision course encounters. It should be noted that, as a safety
measure, the ASL and the ScanEagle maintained a minimum altitude separation of 500 ft during each encounter.

DATA RECORDED
Figure 5 shows an example image from the SAA system when the
5 mm lens configuration was tested. The figure shows the threat
aircraft, the ASL, at a range of 1 km. The figure also shows that the
inhomogeneous cloudy conditions create a complex image background that makes aircraft detection challenging.
We achieved a very high data collection success rate from the
22 collision-course encounters. In one encounter, however, the prevailing wind caused the ScanEagle to fly with an excess crab angle,
which placed the threat aircraft near the edge of the relatively narrow FOV provided by the 8 mm lens. This encounter emphasised
the potential influence of the operating environment on the design
of an SAA system.
Our tests were planned to provide sufficient lead-time, before
detection, so that the maximum detection range of the system
could be determined. The threat aircraft flew for several minutes
before it was visible in the images provided by the SAA system.
We collected datasets in a range of cloud conditions that covered
the more challenging range of complex texture backgrounds and
light-rain conditions.
Three hours of imagery data were recorded from onboad the
ScanEagle. This total consisted of straight-and-level, orbiting, and
collision-manoeuvring phases of flight. The collision-course en-

IEEE A&E SYSTEMS MAGAZINE

SEPTEMBER 2016

Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine September 2016