Aerospace and Electronic Systems Magazine November 2016 Tutorial X - 85

Fasano et al.
link. Consequently, the UA is steered as directed. This scenario is illustrated in Fig. 2.
2. Sensing takes place on the ground. Processed sensor information is transmitted from the ground sensor to the GCS, where
it is evaluated by the pilot, who (with the help of GCS processing) decides if an action needs to be taken to avoid a target
aircraft, and what that action is. The pilot transmits control
actions up to the UA, which then is steered as directed. This
scenario is illustrated in Fig. 3.
3. Sensing takes place on the UA. Processed sensor information is
evaluated by an automated onboard processing capability that
decides if an action needs to be taken to avoid a target aircraft,
and what that action is. The onboard capability transmits control actions up to the UA, which then is steered as directed.
This scenario is illustrated in Fig. 4.
As a general concept, exploiting off-board systems simplifies technological challenges, especially regarding sensing tasks
and compatibility with aircraft budgets [size, weight, and power
(SWaP)]. Indeed, ground-based architectures can work with little
or no modifications of existing UAS designs. However, possible
drawbacks of this approach are the limited coverage of ground systems and the dependency on C2 link. As a consequence, off-board
SAA is usually considered to be a near-term solution for meeting
requirements to enable integration in limited operational areas [5,
6], while onboard SAA is the definite key goal to be accomplished
for future systems.
Regarding sensing, information sources can be classified as
cooperative instruments, wherein an aircraft is equipped with a
transponder to interrogate and/or broadcast information, and
noncooperative sensors, which are able to detect targets autonomously. Noncooperative sensing systems can involve active or
passive sensors, depending on whether or not they transmit the
energy that is needed for object detection. Radar and light detection and ranging (LIDAR) are examples of active sensors, while
electro-optical (EO) cameras are the main example in the passive
category. As mentioned above, noncooperative sensors can be
based on the aircraft or on the ground, providing fundamentally
different perspectives-sensors onboard the aircraft will provide
an aircraft-centric view, while sensors on the ground will provide
an environment-based view. All of these aspects of sensing are
discussed in Section III.
Regarding the detect function, there are a variety of different potential solutions to fulfill the general requirement of using sensor information to determine the level of threat. Starting
from the simple concept of alerting the pilot when an obstacle
is sensed within a given field of regard, more complex solutions include refining sensor information, producing indirect
estimates related to obstacle motion, and predicting the obstacle
path and possibly its associated uncertainty. Other approaches
attempt to evaluate collision risk without an explicit prediction
of obstacle trajectory. Conflict detection is usually associated
with the definition of a safety volume that is not to be violated,
which can be defined in different ways. These issues are discussed in Section IV.
NOVEMBER 2016, Part II of II

Fig. 2.

SAA scenario 1.

Fig. 3.

SAA scenario 2.

Fig. 4.

SAA scenario 3.

Finally, avoidance strategies comprise a range of techniques, starting from basic actions (e.g., descend or land), to
considering more complex maneuvers that consider environmental factors, all with a distinction between remotely operated methods and automated solutions. These will be described
in Section V.
A general taxonomy of SAA systems is presented in Fig. 5.

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Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine November 2016 Tutorial X