Making Underwater Gliders Useful to Navy Operations

AbstractThe depth-average velocity is routinely calculated using data from underwater gliders. The calculation is a dead reckoning, where the difference between the glider’s velocity over ground and its velocity through water yields the water velocity averaged over the glider’s dive path. Given the accuracy of global positioning system navigation and the typical 3–6-h dive cycle, the accuracy of the depth-average velocity is overwhelmingly dependent on the accurate estimation of the glider’s velocity through water. The calculation of glider velocity through water for the Spray underwater glider is described. The accuracy of this calculation is addressed using a method similar to that used with shipboard acoustic Doppler current profilers, where water velocity is compared before and after turns to determine a gain to apply to glider velocity through water. Differences of this gain from an ideal value of one are used to evaluate accuracy. Sustained glider observations of several years off California and Palau consisted of missions involving repeated straight sections, producing hundreds of turns. The root-mean-square accuracy of depth-average velocity is estimated to be in the range of 0.01–0.02 m s−1, consistent with inferences from the early days of underwater glider design.

Download Full-text

An irregularly shaped warm eddy observed by Chinese underwater gliders

Journal of Oceanography ◽

10.1007/s10872-018-0490-0 ◽

2018 ◽

Vol 75 (2) ◽

pp. 139-148 ◽

Cited By ~ 9

Author(s):

Qiu Chunhua ◽

Mao Huabin ◽

Wang Yanhui ◽

Yu Jiancheng ◽

Su Danyi ◽

...

Keyword(s):

Underwater Gliders ◽

Warm Eddy

Download Full-text

Cyclonic Eddies in the Gulf of Mexico: Observations by Underwater Gliders and Simulations by Numerical Model

Journal of Physical Oceanography ◽

10.1175/jpo-d-14-0138.1 ◽

2015 ◽

Vol 45 (1) ◽

pp. 313-326 ◽

Cited By ~ 30

Author(s):

Daniel L. Rudnick ◽

Ganesh Gopalakrishnan ◽

Bruce D. Cornuelle

Keyword(s):

Gulf Of Mexico ◽

General Circulation ◽

Circulation Model ◽

Atlantic Water ◽

Momentum Balance ◽

Loop Current ◽

Massachusetts Institute Of Technology ◽

Underwater Gliders ◽

Flow Curvature ◽

Institute Of Technology

AbstractCirculation in the Gulf of Mexico (GoM) is dominated by the Loop Current (LC) and by Loop Current eddies (LCEs) that form at irregular multimonth intervals by separation from the LC. Comparatively small cyclonic eddies (CEs) are thought to have a controlling influence on the LCE, including its separation from the LC. Because the CEs are so dynamic and short-lived, lasting only a few weeks, they have proved a challenge to observe. This study addresses that challenge using underwater gliders. These gliders’ data and satellite sea surface height (SSH) are used in a four-dimensional variational (4DVAR) assimilation in the Massachusetts Institute of Technology (MIT) general circulation model (MITgcm). The model serves two purposes: first, the model’s estimate of ocean state allows the analysis of four-dimensional fields, and second, the model forecasts are examined to determine the value of glider data. CEs have a Rossby number of about 0.2, implying that the effects of flow curvature, cyclostrophy, to modify the geostrophic momentum balance are slight. The velocity field in CEs is nearly depth independent, while LCEs are more baroclinic, consistent with the CEs origin on the less stratified, dense side of the LCE. CEs are formed from water in the GoM, rather than the Atlantic water that distinguishes the LCE. Model forecasts are improved by glider data, using a quality metric based on satellite SSH, with the best 2-month GoM forecast rivaling the accuracy of a global hindcast.

Download Full-text