Estimating uncertainty in subsurface glider position using transmissions from fixed acoustic tomography sources

Abstract

Four acoustic Seagliders were deployed in the Philippine Sea November 2010 to April 2011 in the vicinity of an acoustic tomography array. The gliders recorded over 2000 broadband transmissions at ranges up to 700 km from moored acoustic sources as they transited between mooring sites. The precision of glider positioning at the time of acoustic reception is important to resolve the fundamental ambiguity between position and sound speed. The Seagliders utilized GPS at the surface and a kinematic model below for positioning. The gliders were typically underwater for about 6.4 h, diving to depths of 1000 m and traveling on average 3.6 km during a dive. Measured acoustic arrival peaks were unambiguously associated with predicted ray arrivals. Statistics of travel-time offsets between received arrivals and acoustic predictions were used to estimate range uncertainty. Range (travel time) uncertainty between the source and the glider position from the kinematic model is estimated to be 639 m (426 ms) rms. Least-squares solutions for glider position estimated from acoustically derived ranges from 5 sources differed by 914 m rms from modeled positions, with estimated uncertainty of 106 m rms in horizontal position. Error analysis included 70 ms rms of uncertainty due to oceanic sound-speed variability.

The North Pacific Acoustic Laboratory deep-water acoustic propagation experiments in the Philippine Sea

“…The detailed results from these experiments, as well as related analyses, will appear in a series of papers, including at present Colosi et al (2013), Freeman et al (2013), Heaney et al (2013), Powell et al (2013), Van Uffelen et al (2013), and White et al (2013). The selected results presented here have emphasized the ambient noise measurements only because those analyses are among the more straightforward.…”

“…Four acoustic Seagliders were deployed during November 2010 in the vicinity of the PhilSea10 moored array (Howe et al, 2011;Van Uffelen et al, 2013). The gliders measured temperature and salinity in the upper 1000 m of the ocean between the moorings and recorded the transmissions from the moored acoustic sources.…”

“…Temperature and salinity measurements in the upper 1000 m were also collected by Seagliders transiting between the moorings during PhilSea10 (Howe et al, 2011;Van Uffelen et al, 2013 Powell et al, 2013), together with the PhilSea10 mooring locations.…”

Diversity-based acoustic communication with a glider in deep water

“…More recently, GPS-based surface positions have been combined with subsurface position estimates derived from acoustic signals that were transmitted for the purpose of performing acoustic tomography. 6 This letter explores the potential of using the gliders with a single hydrophone for long-range acoustic communication in deep water. This is motivated by the recent demonstration of basin-scale acoustic communication 7 which exploits either (a) spatial diversity provided by a vertical array or (b) temporal diversity provided by the time-varying ocean itself with a single stationary receiver.…”

Multipurpose Acoustic Networks in the Integrated Arctic Ocean Observing System

“…Previous studies (e.g., Mikhalevsky, 2002, 2006) suggest that low-frequency (10 -100 Hz) systems could provide basin-scale geolocation, underwater "GPS," in ice-covered environments, but such systems have not yet been implemented. New results of estimating the uncertainty in subsurface glider position using transmissions from fixed 200 -300 Hz acoustic tomography sources at ranges up to 700 km in the Philippine Sea are very promising (Van Uffelen et al, 2013).…”