Modelling of unmanned aircraft visibility for see-and-avoid operations

With more unmanned aircraft (UA) becoming airborne each day, an already high manned aircraft to UA exposure rate continues to grow. Pilots and rulemaking authorities realize that UA visibility is a real, but unquantified, threat to operations under the see-and-avoid concept. To finally quantify the threat, a novel contrast-based UA visibility model is constructed here using collected empirical data as well as previous work on the factors affecting visibility. This work showed that UA visibility <1300 m makes a midair collision a serious threat if a manned aircraft and a UA are on a collision course while operating under the see-and-avoid concept. Similarly, this work also showed that a midair collision may be unavoidable when UA visibility is <400 m. Validating pilot and rulemaking authority concerns, this work demonstrated that UA visibility distances <1300 and