Loran-Based Buoy Position Auditing Systems. Analytical Evaluation

An analytic evaluation and comparison of the following candidate Buoy Position Auditing System (BPAS) configurations is presented in this report: transmission of digital Time Difference (TD) data from a Loran-C receiver on the buoy, retransmission of Loran-C pulses from the buoy, and combination of helicopter Loran-C data and helicopter-to-buoy microwave ranging data in a variable geometry solution. The candidate BPAS configurations utilize Loran-C in the differential mode. A model is developed to characterize differential Loran-C errors, accounting for the expected effect of the land/sea water conductivity interface. The error model is utilized alone, or with a microwave ranging system error model, to estimate buoy position-fix accuracy afforded by each BPAS configuration. Accuracy estimates and data on cost, complexity, and technical risk are employed to recommend a BPAS configuration for testing. It is concluded that Loran-C pulse retransmission is not a viable BPAS configuration. The variable geometry BPAS configuration is highly accurate, due to calibration of Loran-C errors by processing of redundant data, but is not presently cost-effective. The digital TD transmission BPAS configuration is recommended for testing, due to its simplicity and low cost.