Underwater glider reliability and implications for survey design

It has been 20 years since the concept of Autonomous Oceanographic Sampling Network (AOSN) was first introduced. This vision has been brought closer to reality with the introduction of undersea gliders. Whilst in terms of functionality the undersea glider has shown to be capable of meeting the AOSN vision, in terms of reliability there is no community-wide hard evidence on whether persistent presence is currently being achieved. This paper studies the reliability of undersea gliders in order to assess the feasibility of using these platforms for future AOSN. The data used is taken from 205 deployments of gliders by 12 European laboratories between 2008 and 2012. Risk profiles were calculated for two makes of deep underwater glider; there is no statistically significant difference between them. Regardless of make the probability of a deep undersea glider surviving a 90 day mission without pre-mature mission end is approximately 0.5. The probability of a shallow undersea glider surviving 30 day mission without premature mission end is 0.59. This implies that to date factors other than the energy available are preventing undersea gliders achieving their maximum capability. This reliability information was used to quantify the likelihood of two reported undersea glider surveys meeting the observation needs for a period of 6 months and to quantify the level of redundancy needed to in order to increase the likelihood of meeting the observation needs.