A Flight State Estimator That Couples Stereo-Vision, INS, and GNSS Pseudo-Ranges to Navigate with Three or Less Satellites
This paper presents a flight state estimator which couples stereo vision, inertial (INS), and global navigation satellite system (GNSS) data. The navigation filter comes with different operation modes that allow loosely coupled GNSS/INS positioning and, for difficult conditions, improvements using %satellite augmentation systems (SBAS), visual odometry and a tighter coupling with GNSS pseudo-range (PSR) data. While camera systems are typically used as an additional relative movement sensor to enable positioning without GNSS for a certain amount of time, the PSR data filtering allows to use satellite navigation also when less than four satellites are available. This makes the filter even more robust against temporary dropouts of the full GNSS solution. The application is the navigation of unmanned aircraft in disaster scenarios which includes flights close to ground in urban or mountainous areas. The filter performance is evaluated with sensor data from unmanned helicopter flight tests where different conditions of the GNSS signal reception are simulated. It is shown that the use of PSR data improves the positioning significantly compared to the dropout when the signals of less than four satellites are available.