Unified Surveillance: The Comprehensive Detect-and-Avoid Solution

Jun 2, 2021

An edited version of this article was originally published on UASVision.com on June 1, 2021.

Beyond Visual Line of Sight (BVLOS) flight for unmanned aircraft systems (UAS) will enable repeatable, scalable and regularized operations. Detect-and-Avoid (DAA) technologies, in turn, enable BVLOS ops. These routine advanced operations will require an awareness solution arguably just as complex as the airspace itself. Recognizing this, regulators and standards bodies have included ground based surveillance systems (GBSS) as one of the key enablers for extended operations in all classes of airspace and for Unmanned Traffic Management (UTM). Surveillance must not only be comprehensive, but unified, for the industry to reach new heights. 


The Radio Technical Commission for Aeronautics (RTCA) is an independent and collaborative public-private Standards Development Organization, which has been working on the DAA problem for years. RTCA has focused on larger UAS, up and away, over 500 feet (ft) above ground level. Its Special Committee 228 incorporated ground-based DAA into several of its minimum operating performance standards. The DO-381 standard provides performance requirements for the approaches to the terminal area of airports. It includes ground radar as part of an overall traffic surveillance solution. 

The draft DO-381A, which adds the en route environment, contains GBSS characteristics standards for designers, manufacturers, installers, and users of equipment for larger UAS that will be either performing extended operations in all classes of airspace, except Class A. According to Andy Thurling, the Chief Technology Officer for Northeast UAS Airspace Integration Research (NUAIR), who is also a contributor to RTCA standards, the group has moved away from a single ground-based radar-solution in earlier DO-381 drafts to using the sensor-agnostic term “surveillance system” in the published version. He explains, “GBSS’ could include acoustic, optical, radar, or other solutions. We need to be inclusive of any technology that achieves the required performance. A new version of DO-381 is in the works that will enable en route in addition to terminal operations.” 

ASTM International (ASTM)

Whereas the RTCA’s airspace integration efforts revolve primarily around Class D airspace and higher, ASTM, another globally-recognized and consensus-based standards organization, has been looking at what Thurling, who is also the ASTM DAA Performance Requirements lead, describes as, “UTMish” airspace (mostly Class G). There are currently three active ASTM DAA-related groups, WK74215, updating F3442-20 DAA Performance Requirements, WK62669 DAA Testing Requirements and WK69690 Surveillance UTM Supplemental Data Service Provider (SDSP). 

ASTM published F3442-20 in July 2020. It defines DAA system performance requirements for smaller UAS BVLOS flights in lower altitude airspace. It includes the Airborne Collision Avoidance System (ACAS) sXu as a “reference architecture.” According to a Stanford University article, “ACAS sXu applies to smaller UAS and provides a single level of alerting and guidance, with the separation volume scaled based on intruder type. ACAS sXu includes real-time dynamic scaling, meaning that the separation volumes provided by the system can be adjusted in real-time based on system inputs and states.” Onboard DAA systems are only part of the total solution. F3442-20 and ACAS sXu also accommodate a blended solution that could include ground-based tech.  

RTCA and ASTM are collaborating on their DAA efforts because their airspace “lanes” overlap a bit, particularly in “medium risk” (as defined by JARUS) airspace. For this reason, like RTCA’s draft DO-381A, the ASTM Surveillance UTM SDSP working group strives to ensure that any surveillance system also remains technology-neutral. ASTM WK74215 continues to review both airborne and ground sensors for cooperative aircraft detection, such as ADS-B, transponders, remote identification, as well as non-cooperative detection, including radar, acoustic, and electro-optical/infrared. The updated DAA Performance Requirements standard is expected to be published in the next five to six months.

The Federal Aviation Administration (FAA)

The FAA’s UTM Concept of Operations version 2.0., published in March 2020, aligns with RTCA and ASTM DAA standards. It includes requirements for conflict advisory, alert, and surveillance as a set of strategic and tactical services to support the UTM safety case.

The European Union Aviation Safety Agency (EASA)

Also in March 2020, the EASA published its draft U-Space regulation, finalized in 2021, outlining the European Union’s UTM system. The U-Space regulation, which will be effective in 2023, requires third-party U-space service providers (USSPs) to provide various services. Relevant to the DAA discussion, traffic information services are one of four required USSP services, which also include flight authorizations for controlled and uncontrolled airspace, geo-awareness information about UAS geographic zones, and network identification (NetworkID) to track drones through both network and broadcast-out to other providers and operators. Traffic information services can include ground based surveillance systems (GBSS).

The Joint Authorities for Rulemaking on Unmanned Systems (JARUS)

The JARUS is also working on an Annex to the Specific Operations Risk Assessment (SORA), which will provide a methodology for Operators to claim “credit”  for UTM services in their safety case, including surveillance services called the Tactical Conflict Detection and Alerting Safety Service (TCDASS). It is anticipated that the Annex will, like other aspects of the SORA, focus on proportional operational risk. Low risk operations will need a lower level of assurance. Medium risk will require medium assurance, including surveillance and alerting. Expect to see GBSS concepts included in the Annex.


The EUROCAE, a membership-based non-profit standards organization, continues to develop five different standards that relate to DAA, including one on traffic information. The European Commission selected EUROCAE to write Means of Compliance for the U-Space Rule relating to NetworkID service, geo awareness, and traffic information as well as the standard for aeronautical data, or the common information service. It remains to be seen whether or not the group incorporates GBSS in these standards consistent with all other standards bodies.

The Unified Surveillance Solution

Effective DAA will require a system of systems approach. According to Thurling, “You can’t do BVLOS without a surveillance system, either on board, off board, or a blend of the two.” The key is to enable awareness of potentially encroaching aircraft, from surveillance volume, through declaration volume and before it gets too close to the operational volume and becomes a threat to a UAS conducting mission operations. Surveillance volume is defined by how long it takes to build a track to make a declaration that the aircraft is approaching. Declaration volume is based mostly on the speed of the encroaching aircraft and the time it takes the drone to make a maneuver to remain well clear of the other aircraft.

Credit: RTCA

Iris Automation’s Casia® series of onboard integrated computer vision systems provides robust situational information and intelligent decision-making in real time to avoid mid-air collisions. Combining this tech with ground based surveillance systems (GBSS), such as DAA systems fixed on the ground around the work area perimeter, could provide a perimeter of sanitized airspace enabling UAS to safely operate missions at scale. Such a system would constantly monitor the airspace around a perimeter to detect potential mid-air collisions, alert the pilots in command (PIC) of risk, and permit him or her to safely maneuver out of the potential intruder’s path either manually or autonomously. 

Iris Automation also contributes to the ASTM DAA-related groups, and believes optical on-board and ground-based systems like these could meet detection performance requirements for certain risk-ratios. According to Iris’ CEO, Jon Damush, “The potential benefits of this Casia-GBSS solution, which would enhance airspace protection through deconfliction, include increased scale and efficiency across a range of UAS operations, from active disaster areas, construction sites, mining, perimeter inspections, across college campuses, golf courses and border corridor operations. We are encouraged that many different standard development organizations are on track to finalize key surveillance standards. This will allow us to certify to them, deploy these critical systems, and move the UAS industry forward into next level operations that will benefit all.”

Jonathan Daniels, the contracted Program Lead for the NYUASTS on Advanced Air Mobility High-Density Vertiport Automation for NASA and the CEO of Praxis Aerospace Concepts International, a Service-Disabled Veteran-Owned Small Business headquartered in southern Nevada that provides practical solutions for multi-modal ground-air-sea-industrial response robot systems and infrastructure, agrees with both Damush and Thurling: we need holistic solutions and need them soon. An ASTM Fellow, he also works with Thurling on the ASTM F38 Executive Committee. Daniels, however, would take the DAA solution one step further, requiring what he has coined “unified surveillance.”

Daniels explains, “Unified communications is a term first used to describe a phone system which integrated multiple communications methods, such as text and video, with different physical layers, like WIFI, LTE and RF, so as to appear seamless for the user. Similarly, we need GBSS and all other surveillance options to become ‘unified surveillance.’ This means we need to integrate not just surveillance systems but multiple sources of information (radar, acoustic, ADS-B IN, RID, etc.) with different protocols (vehicle-to-vehicle or and vehicle-to-infrastructure) to create a seamless collaborative environment for all aviation users. Think of this in terms of common driving apps like Waze™ or Google Maps™ that use crowd-sourced information to inform and improve driving experiences. This is the necessary evolution.”

Daniels is not alone in his thinking: GBSS is part of the surveillance solution and that surveillance needs additional communications links to truly accelerate the industry. In February 2021, the Global UTM Association and GSMA collaborated to produce a definition that harmonizes the interfaces of data exchanges between mobile network operators (MNOs) and various aviation systems as part of the overall UTM system, the Aerial Connectivity Joint Activity Interface for Data Exchange between MNOs and the UTM Ecosystem NetworkCoverage Service Definition v1.00 Feb 2021. Thomas Neubauer, Vice President of Innovations at TEOCO, spearheaded this effort, which provides the means to bridge and harmonize how data will be exchanged between MNOs, aviation systems and UAS PICs. The Europeans intend to test out these concepts in the Fall of 2021, as part of the GOF 2.0 Integrated Urban Airspace Validation. According to Neubauer, “Network connectivity is a must have for safe airspace integration. This new definition opens the door to reliable, feasible, available and scalable beyond visual line of sight (BVLOS) and complex operations. The GOF 2.0 trials will be our final proving ground.”

The day is near when we will effectively achieve air and ground multi-sensor fusion and integrate data from multiple other sources that “talk” to each other and with the humans that need the information to make operational decisions. When we do, the UAS industry will truly take off!

Dawn M.K. Zoldi (Colonel, USAF, Retired) is a licensed attorney with 28 years of combined active duty military and federal civil service to the Department of the Air Force. She is an internationally recognized expert on unmanned aircraft system law and policy, a columnist for several magazines,recipient of the Woman to Watch in UAS (Leadership) Award 2019, President and CEO of UAS Colorado and the CEO of P3 Tech Consulting LLC. For more information, visit her website at: https://www.p3techconsulting.com.


  1. http://theory.stanford.edu/~barrett/pubs/LRM+19.pdf
  2. https://www.gsma.com/iot/wp-content/uploads/2021/02/ACJA-NetworkCoverage-Service-Definition-v1.00.pdf