GPS World, April 2016

AUTONOMOUS NAV providing a GPS free relative distance observation in situations where GPS is blocked due to airframe masking jamming and so on Data from both active lidar and passive camera vision sensors were added to the system providing significant advantages in the process flow The use of vision sensors provides the relative distance observation in GPSdenied conditions for continuity in R EKF updating In addition visionbased relative distance allows for the detection of outliers by evaluating the redundancy contribution of the measured GPS based relative distance and enables the transfer of the R TSPI solution from the secondary refueling center to the on the fly probe drogue system as shown in FIGURE 6 For the active vision system we leveraged a fully integrated lidar mapping payload as shown in FIGURE 7 LEFT For the passive sensor we utilize a stereo camera FIGURE 7 RIGHT shows the test area and the simulated drogue Imagery observations from the passive camera and the lidar system were processed with independent algorithms appropriate to each data type and the relative distance between each of the two sensors and the simulated drogue was measured with an RMS error of less than 10 cm INTEGRITY While outside the scope of this article in addition to supplying a GPS free relative distance observation the use of vision sensors was applied to the task of increasing system integrity This includes in general the capability to indicate when the system should not be used for the intended operation We focused on two aspects outlier detection inner reliability and the effect of undetected outliers outer reliability To properly address the reliability and integrity requirements a quality testing mechanism was designed to FIGURE 6 Vision sensor aiding increasing the integrity FIGURE 7 Geo MMS left and its application right for measuring relative distance assess the estimated predicted relative distance observations before passing them in to the R EKF module CONCLUSIONS An autonomous relative navigation in its application for the aerial refueling problem places special attention on system architecture so that it can handle most possible real world scenarios including frequent data link dropouts data link latency and GPS outages The core of the system is a relative extended Kalman filter which uses GPS and IMU measurements of the primary and secondary platforms to estimate the relative inertial navigation states The system is able to provide relative TSPI at the IMU sample rate with an accuracy of 10 m position 01 m s velocity and 05 º attitude An added benefit of the system architecture is the ability to add observation models that do not rely on GPS Thus redundancy can be introduced using sensors such as vision systems 24 GPS WORLD WWW GPSWORLD COM APRIL 2016 SHAHRAM MOAFIPOOR is a senior navigation scientist at Geodetics focusing on new sensor technologies sensor fusion architectures application software embedded firmware and sensor interoperability in GPS and GPS denied environments He holds a Ph D in geodetic science from The Ohio State University JEFFREY A FAYMAN serves as Geodetics CTO He holds a Ph D in computer science from the Technion Israel Institute of Technology and has published more than 40 papers in robotics computer vision computer graphics and navigation systems LYDIA BOCK serves as Geodetics president and CEO She has more than 35 years of industry experience spanning a variety of high tech industries including electronics semiconductors and telecommunications She has a Ph D from the Massachusetts Institute of Technology DAVID HONCIK Geodetics director of engineering has more than 30 years of experience in software hardware integration and structured software design for real time embedded systems Windows programs graphics telecommunications aerospace flight simulation and airborne instrumentation The integrated lidar mapping payload referenced is Geodetics Geo MMS system