Acoustic Position Measurement,an Overview

Abstract

Acoustic Position Measurement,an Overview Thomas R. Stockton; Thomas R. Stockton Delco Electronics Search for other works by this author on: This Site Google Scholar Miles W. McLennan Miles W. McLennan Delco Electronics Search for other works by this author on: This Site Google Scholar Paper presented at the Offshore Technology Conference, Houston, Texas, May 1975. Paper Number: OTC-2172-MS https://doi.org/10.4043/2172-MS Published: May 04 1975 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Stockton, Thomas R., and Miles W. McLennan. "Acoustic Position Measurement,an Overview." Paper presented at the Offshore Technology Conference, Houston, Texas, May 1975. doi: https://doi.org/10.4043/2172-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search nav search search input Search input auto suggest search filter All ContentAll ProceedingsOffshore Technology ConferenceOTC Offshore Technology Conference Search Advanced Search ABSTRACTAcoustic position measurement is accomplished by measuring the relative location between a reference" sound source and a receiving array. When a position measurement is to be taken the source emits a "ping," a short burst of high frequency acoustic sine waves. The ping propagates through the water and is received at an array of hydrophones. The measured time of arrival at each hydrophone is used to estimate the position of the sound source with respect to the array.There are two fundamental measurement modes depending on whether the emission time of the source ping is known. When the source time is known, the solution is in the form of intersecting spheres (spherical tracking). If the time of the ping is not known, the measurement problem is the equivalent of solving for the intersection of hyperbolodial surfaces (hyperbolic tracking).Position measurement uncertainties are due to inexact knowledge of hydrophone location, ping arrival time, and sound velocity. Each of these errors can have a random and/or bias component. The manner in which these errors are reflected into position measurement uncertainties is governed by geometry and the measurement mode.Factors of array geometry which affect measurement accuracy are the number of elements, their pattern, and separation. When the array is ship mounted, corrections for ship attitude must also be included in the measurement process. Errors in attitude correction are similar to uncertainties in array element location.The basic concept is discussed, generalized equations are developed, and the affect upon the equations of simplified array patterns and simplifying approximations is examined. Finally, the inaccuracies imposed by each error source are discussed, and position error contour curves for typical measurement geometries are presented.BASIC CONCEPTAcoustic position measurement, or acoustic tracking, is a means of measuring the relative positions of objects under water. The basic measurement is the transit time of short acoustic pulses (pings) from specially designed underwater loudspeakers (termed acoustic projectors or pingers) to underwater microphones (termed hydrophones). Since the sound travels at a very nearly constant velocity (around 5,000 ft/sec), the range between projector and hydrophone can be determined by multiplying the measured transit time by the sound velocity. A complete measurement system will consist of multiple projectors and hydrophones. Several of these will be at known locations in whatever coordinate system is being used. Acoustic measurements of the range between the "knowns" and the "unknowns" allows location of the' unknown by trigonometric calculation. A quick understanding of the basic principles may be gained by considering some examples.SPHERICAL TRACKINGAssume the tracking area to be a plane containing two hydrophones and a pinger. The known points are the two hydrophones, HI and HZ' and the unknown is the pinger located at P. (See Figure 1.) A ping emitted at time to travels outward from P and is received at HI and HZ at times t1 and t2, respectively. Keywords: hydrophone, equation, pinger, reservoir characterization, slant range, correction, hydrophone array, arrival time, displacement, ship Subjects: Reservoir Characterization, Information Management and Systems This content is only available via PDF. 1975. Offshore Technology Conference You can access this article if you purchase or spend a download.