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We have reported on an acoustic Doppler navigation system for ocean use in several publications [R. P. Porter, R. C. Spindel, and R. J. Jaffee, J. Acoust. Soc. Am. 53, 1691–1699 (1973); R. C. Spindel, R. P. Porter, and R. J. Jaffee, J. Acoust. Soc. Am. 56, 440–446 (1974)]. The system can yield navigation fixes with respect to a bottom-moored, continuous-wave, beacon net with accuracies (on a fix-to-fix basis) of a few centimeters. The system has found use in generating synthetic space-time acoustic apertures where it is necessary to track a receiver to within a fraction of an acoustic wavelength. In order to use the system to best advantage, a survey is required to determine precisely the relative positions of the beacons forming the net. We report here on a navigation system that combines a pulse transponder with a beacon to improve survey accuracy. It measures acoustic travel time between survey platform and mooring, as well as accumulated phase between survey points. Nonlinear regression techniques are employed to develop a maximum-likelihood estimator for mooring positions. An approximate covariance matrix of the estimate errors is generated, and an optimum choice of survey points is indicated. The combined system, using these selected locations for performing the survey, yields mooring coordinate errors of about ±1 m. Improved precision appears to be limited by inaccuracies in the pulse and Doppler measuring systems.

ABSTPACTA high resolution acoustic navigation system for ocean use is being developed at the Woods Hole Oceanographic Institution. The system can yield navigation fixes with respect to a bottom moored reference net with accuracies (on a fix to fix basis) of a few centimeters.In order to use the system to best advantage a survey is required to determine precisely the relative positions of the net elements.Each element combines a pulse transponder with a continuous wave (CW) beacon. Accumulated phase (Doppler shift of the CW beacon) between survey points is measured as well as acoustic travel times between survey points and transponders. Non-linear regression techniques are employed to develop a maximum likelihood estimator for net element positions based on these phase and travel time measurements. An approximate error covariance matrix is generated and an optimum choice of survey points is indicated. The combined system, using these selected locations for performing the survey, can yield reference mooring coordinates with error of ±1 meter. Improved precision appears to be limited by inaccuracies in the pulse and Doppler measuring system.