UC San Diego

Acoustict ravelt ime measurementwse reu sedt o navigatet he elementso f a large-aperture(9 00 m) acoustica rray. Array navigations ystemp erformancew ase valuatedd uring a vertical deploymenitn the northeasPt acificf rom the ResearchP latformF LIP. A networko f bottommooreda coustictr ansponderws erei nterrogatedfr om FLIP and their 12-kHz repliesw ere detectedb y receiversa t 75-m intervalsa longt he array. A nonlinearl east-squareasl gorithm wasu sedt o estimateF LIP and array elementp ositionsfr om the travelt ime measurements. The FLIP positionsd erivedf rom this procedurea greedw ith positionso btainedf rom global positionings ystem( GPS) satelliten avigationt o within a 10-mr mse rror. Navigatedp ositions for FLIP were internallyc onsistenwt ith a 0.5-m meanr ms error and standardd eviationo f 1.1 m, and, for an array element,w ere consistentw ith a 2.8-m mean rms error and standard deviationo f 0.8 m. The resultingti mes erieso f arraya nd FLIP motionsw erea nalyzedw ith respecto wind, tidal, and internalw avef orcingf unctionsW. ind and tidal forcingh ad the greatesti nfluenceo n FLIP motion,w hereasa rray motionw asg overnedb y FLIP movement, tides,a nd higherf requencys ourcesL. ow-frequencya rray motion,w ith periodso n the ordero f hours,w asa resulto f FLIP towingt he array overa horizontalr angeo f 300 m in responsteo the wind and the semidiurnalt idal oscillationst;h e array remainedw ithin a 30-m horizontal range of FLIP's position. Higher frequency array motion had apparent internal wave and surface-couplecdo mponentsT. he array shapew asp rimarily straighta nd nearly vertical,t o within approximatelya 2ø t ilt, respondinga sa simplep endulumw ith smalld isplacements.