Unmanned Aircraft System Navigation in the Urban Environment: A Systems Analysis Journal of Aerospace Information Systems This article from the Journal of Aerospace Information Systems analyzes alternative methods for Unmanned Aerospace Systems (UAS) navigation within urban environments. Navigation accuracy by Global Positioning System (GPS) is severely degraded due to urban canyons, where accuracy is particularly poor. An urban canyon is best described as area flanked by tall buildings. Although Global Navigation Satellite System (GNSS) is unreliable in the vicinity of dense urban structure it can be used in combination with other complimentary sensors to provide position and velocity measurement. Urban UAS missions related to law enforcement, traffic surveillance, riot control, and anti-terrorism are all challenged b...