UAV Sense and Avoid Technology

      With a primary focus on safety, a transition from accommodation to integration of UAS into the national air space (NAS) is a high priority of the FAA.  However, unlike the typical manned aircraft operating in the NAS, which contain sophisticated and well-defined “detect, sense, and avoid” (DSA) avionics for ensuring safe separation between aircraft, most UAS do not carry electronic identification signaling systems.  In this regard, current technology fails to provide UAS with the same level of safety and compliance with FAA regulations as manned aircraft.  Furthermore, many UAS operate in close proximity to the ground where tall buildings, mountains, trees, and other obstacles pose a potential problem for safe operations.  For UAV without DSA the absence of a pilot on board who would see and avoid such objects emphasizes the critical nature of the FAA's requirement for DSA technology in UAVs that operate in the NAS.  As such, the task of detecting, sensing, and avoiding aircraft for safe operation in the NAS without disrupting current air traffic control procedures is of primary importance in the integration of UAS into the NAS.

Detect, Sense, and Avoid

     Currently, separation of manned aircraft in the NAS is controlled by air traffic controllers (ATC) that continuously monitor aircraft operations and larger commercial aircraft carrying traffic alert and collision avoidance systems (TCAS) that perform cooperative DSA functions with smaller aircraft equipped with conventional transponders.  Very large UAV such as the Global Hawk or the Reaper may be configured to support transponders, but the size, cost, and power drain of such a system is generally prohibitive for use in small UAS operations (Gerold, 2006).  As such, current UAS operations in the NAS is limited and tightly controlled by the Federal Aviation Administration (FAA).  Aside from model aircraft operation, all unmanned aircraft require FAA authorization to operate in the NAS.  For public operations (governmental) the FAA issues a Certificate of Authorization (COA), for civil operations (commercial) the FAA issues a Section 333 Exemption, and for research and development the FAA issues a Special Airworthiness Certificate (SAC) in the experimental category (FAA, 2015).

     “Whether a sense-and-avoid system uses electro-optical cameras, laser radar (LIDAR) devices or transponders, the challenge is to make the devices small and light enough to be deployed on small UAVs” (Marshall, 2013, par. 8).  Various solutions to the problem of DSA functions in UAVs include techniques that use radar, visual observers, and manned chase aircraft.  Spearhead by a group of European countries and 11 industrial partners one ambitious effort under way in remotely piloted aircraft systems (RPAS) is the development of an integrated system for UAVs called the Mid-Air Collision Avoidance System (MIDCAS) (Marshall, 2013).
     Other possible solutions such as ground-based sense and avoid (GBSAA) may offer a near-term alternative to line-of-sight before transitioning to Automatic Dependent Surveillance-Broadcast (ADS-B) and the satellite-based Next Generation Air Transportation System (NextGen) due for implementation between 2012 and 2025.  The ground based sense and avoid system utilizes a 3D radar system and algorithms in cooperation with ATC and the UAS ground control station (GCS) to determine if there is a danger of collision and notifies the UAV pilot when their aircraft is on a collision path so an evasive action such as altering the flight path of the UAV may be undertaken (Lopez, 2012).  ADS-B is a next generation satellite based global positioning system (GPS) avionics surveillance technology incorporating both air and ground aspects.  The ADS-B system automatically transmits position and velocity data to the ATC that allows the ATC to monitor and separate aircraft in a more efficient and precise manner than current radar based technology.  Since ADS-B utilizes GPS signals it expands surveillance to areas radar is unable to cover (Universal Avionics System Corp., 2013).  Although still under research, GBSAA and ADS-B provide the potential for an acceptable level of DSA for UAS in the near future.

References

Federal Aviation Administration. (2015). Unmanned Aircraft Systems. Retrieved from http://www.faa.gov/uas/

Gerold, A. (2006, November 1). UAV: Manned and Unmanned aircraft: Can they coexist? Avionics Today. Retrieved from http://www.aviationtoday.com/av/issue/feature/UAV-Manned-and-Unmanned-Aircraft-Can-They-Coexist_6115.html#.VAktHEtJXM0

Lopez, T. (2012, July 5). Radar to allow UAS to fly in national air space. Military News. Retrieved from http://www.military.com/daily-news/2012/07/05/radar-to-allow-uas-to-fly-in-national-air-space.html

Marshall, P. (2013, July 12). The tech that will make drones safe for civilian skies. GCN. Retrieved from https://gcn.com/articles/2013/07/12/drone-uav-sense-and-avoid-technologies-civilian-airspace.aspx