An estimation of the average lifetime of the latest model of APEX floats |
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Authors: | Taiyo Kobayashi Brian A King Nobuyuki Shikama |
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Institution: | (1) Institute of Observational Research for Global Change, Japan Agency for Marine-Earth Science and Technology, Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan;(2) National Oceanography Centre, Southampton, Empress Dock, Southampton, SO14 3ZH, UK |
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Abstract: | Estimating the average lifetime of floats is very important for Argo, because the total cost of maintaining the monitoring
network largely depends on float lifetime. However, the actual lifetime of floats used in Argo is currently unknown. An estimate
can be made by examining past float survival, but this is complicated by floats still operating at sea and continuous improvements
in float hardware. Because APEX (Autonomous Profiling Explorer) floats are the most widely deployed type of float in the world
oceans, in this study we estimate the lifetime of the latest model of APEX powered by alkaline batteries. The expected lifetime
is estimated with a statistical method that allows for floats that are still active and that failed because of a known and
now fixed hardware fault that should not cause failure in the latest model of floats. As an example, we analyzed the APEX
fleets managed by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), because we have access to a JAMSTEC
database in which the causes of float failure have been carefully correlated to known hardware problems. Analysis of the JAMSTEC
fleet (n = 571, as of 7 May 2008) indicated that the expected lifetime of the latest model of APEX is 134.6 (127.6–141.5, considering
standard errors) cycles, equivalent to 3.7 years of 10-day cycles. We conclude that the annual deployment of 813 (773–859)
APEX floats is needed to maintain the Argo observational network of 3000 floats. Floats with different hardware configurations
(e.g., lithium batteries) or different mission programs (e.g., shallower profiling, deeper profiling every several cycles)
may be expected to have an even longer lifetime. |
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Keywords: | Argo project profiling float lifetime |
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