A High-Accuracy, Long-Distance Range Measurement System
D.L. Paquette, Denis M. Coffey · Offshore Technology Conference · 1985
ABSTRACT A recent acoustic experiment, conducted in the North Atlantic, required highly accurate measurements of the range between a towed acoustic source and a deep suspended receiver. Range accuracies on the order of 20 m rms were needed over distances up to 100 nmi. To achieve this objective, a sophisticated system of computer integrated position measurement equipments was developed and insta11ed aboard two research vessels. Included in the system were a bottom mounted transponder positioning system, Trisponder, Argo OM-54, Loran C, a custom designed tow position measurement system, and six tracking. computers with peripherals. An error analysis indicated an achievable accuracy of 8 m rms. Post-test data reconstruction indicated that the system performed as designed and demonstrated the feasibility of integrating a diverse group of equipments to obtain accuracies and reliabilities not possible with one alone. This paper presents a detailed description of the system, summarizes the error analysis, and discusses some of the specific measurement algorithms. INTRODUCTION A series of acoustic propagation experiments was conducted in the North Atlantic in an area about 200 nmi west by northwest of Bermuda during the summer of 1981. The objective of the experiments was to evaluate the accuracy of several acoustic propagation mode1s. A common shortcoming of such mode1sis that oftentimes the basis for judging their accuracy is a comparison of their performance with the performance of other models and/or generally scanty at-sea data. To alleviate this shortcoming, these experiments were set up to collect sufficient data to test the ability of the models to predict the number of operative ray paths, relative path gains, and absolute path delays under a given set of circumstances. The experiments involved towing an acoustic source from one research vessel while receiving the signals on a vertical line array suspended from another. As shown in figure la, the acoustic source was mounted in a "V" fin depressor and towed at 5 to 7 knots at a nominal depth of 100 m. Onboard the tow vessel, referred to as the "p" (Projector) boat, a signal generator, power amplifier, extensive analog and digital data collection system, and the ranging and positioning system, which is the subject of this paper, were mounted. The other research vessel, called the "A" (Array) boat, supported the receiving array and Beam former which extended to depths of 1250 m to 5000 m. Onboard were the receiver, analog and digital data collection equipment, and the remainder of the ranging and positioning system. This paper presents a description of the systems and techniques used to measure the projector/array separation. Included is an explanation of the major mathematical algorithms used and a sample error estimation calculation. Figure 1b is a plan view of the two vessels showing the array, projector, and their respective coordinate systems. The vessels were 2 nmi a part at the start of the experiments.