The AirStar-a precision GPS parallel swath guidance and tracking system

Aerial spraying from aircraft for agricultural and forestry applications is a multi-million dollar business. Until very recently, the pilots have been forced to rely on human flaggers or more expensive and less accurate techniques for positioning the aircraft (e.g. Loran-C). With the advent of commercially available differential GPS systems for aerial application, this industry is presently undergoing major changes in manpower requirements and operational procedures. Environmental, regulatory, legal, and economic aspects of this industry will also be significantly altered in the near future. This paper describes in detail the SATLOC AirStar system and its associated components. GPS receiver performance requirements are extremely demanding for this application and position update rate, dynamic tracking capability, and satellite re-acquisition time are reviewed. Positioning performance test results using high resolution video and optical alignment methods for control are then examined. Both the absolute and relative alignment accuracies are presented using both land vehicles and aircraft. The ability of an operator to consistently follow pre-determined ground patterns using the AirStar equipment is also assessed. External system components which add utility unique to aerial application and post-flight plotting software are also discussed