High resolution frequency-wavenumber spectrum analysis.

Navigation parameters (position, velocity, and attitude) can be estimated using optical measurements combined with an inertial navigation system. This can be accomplished by tracking stationary optical features in multiple images and using the resulting geometry to estimate and remove inertial errors. A critical factor governing the performance of image‐aided inertial navigation systems is the robustness of the feature tracking algorithm. Previous research has shown the benefit of coupling the sensors at the measurement level using a tactical‐grade inertial sensor. While the tactical‐grade sensor is a reasonable choice for larger platforms, the greater size and cost of the sensor limits its use in smaller platforms. In this paper, an image‐aided inertial navigation algorithm is implemented using a multidimensional stochastic feature tracker and low‐cost sensors. The performance of the resulting navigation system is evaluated and compared. The fused image‐inertial sensor is shown to outperform a free‐running tactical‐grade inertial sensor.

There is currently great interest in using regional-area reference receiver networks to perform precise positioning using GPS carrier-phase measurements. The NetAdjust algorithm described herein uses a network of reference receivers to significantly increase the distance over which kinematic carrier-phase ambiguity resolution can be performed. When using this algorithm, information from the reference receiver network is encapsulated into the measurements from a single reference receiver so that standard ambiguity resolution techniques can be used between that reference receiver and a mobile receiver. The NetAdjust method is applied to a 400 km = 600 km network of 11 reference stations positioned throughout Norway. The NetAdjust algorithm yielded significant reductions in differential errors, and it improved positioning performance. Most important, NetAdjust demonstrated a significant improvement in the ability to resolve widelane carrier-phase integer ambiguities and a modest improvement in the ability to resolve L1 ambiguities. Results are presented for a number of different network configurations.

The Global Positioning System (GPS) Operational Control Segment (OCS) generates predicted satellite ephemerides and clock corrections that are broadcast in the navigation message and used by receivers to estimate real-time satellite position and clock corrections for use in navigation solutions. Any errors in these ephemerides will directly impact the accuracy of GPS based positioning. This study compares the satellite position computed using broadcast ephemerides with the precise position provided by the International GPS Service for Geodynamics (IGS) Final Orbit solution. Similar comparisons have been undertaken in the past, but for only short periods of time. This study presents an analysis of the GPS broadcast ephemeris position error on a daily basis over the entire period 14 Nov 1993 through to 1 Nov 2001. The statistics of these errors were also analysed. In addition, the satellite position computed using the almanac ephemeris was compared to the IGS precise final orbit to determine the long-term effect of using older almanac data. The results of this research provide an independent method for the GPS Joint Program Office (JPO) and the OCS to gauge the direct impact of Kalman filter modifications on the accuracy of the navigational information available to the GPS users. GPS engineers can compare future Kalman filter changes to the historical baseline developed by this thesis and readily assess the significance of each proposed engineering change. Subject TermsGPS, Global Positioning, Ephemeris, Ephemerides, Navigation, Error, Almanac, Broadcast Report Classification unclassified Classification of this page unclassified Classification of Abstract unclassified Limitation of Abstract UU Number of Pages

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