How sustainable is the global Argo array? Survival analysis of 20,619 floats, coverage of the design target and a fleet renewal model, 2000–2026
Küresel Argo dizisi ne kadar sürdürülebilir? 20.619 şamandıranın sağkalım analizi, tasarım hedefinin kapsanması ve filo yenileme modeli, 2000–2026
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Abstract
Argo profiling floats are the main source of knowledge on the heat and salt content of the ocean, and the continuity of the array depends entirely on annual deployments. This study treats the sustainability of the array as a reliability and renewal problem. The lifetimes of 20,619 floats deployed between 2000 and 2026 are extracted from the profile index of the global data assembly centre; survival is analysed with Kaplan–Meier, Weibull and Cox models, the monthly coverage of the 3°×3° design cells is compared with random and perfect placement benchmarks, and fleet size is projected with a renewal model. Median lifetime rose from 3.0 years for 2000–2004 deployments to 5.0 years for 2015–2019 deployments, whereas the loss rate within the first year has stayed in the 10–13% range for twenty years. The fleet has been around four thousand floats since 2016, but the share of design cells between 60°S and 60°N occupied by a float at any one time has levelled off at 65%, and the share with at least one profile in a month at 75%. Snapshot coverage is below the value expected if the same number of floats were placed at random (69%); placement efficiency has been negative since 2005 (−0.10), i.e. the array is slightly more clustered than a random placement. 58% of active floats are handled by a single data centre. The deployment rate of the last three years (781 floats per year) is roughly enough to maintain the present fleet; the 4,700-float target requires 838–913 deployments per year. A 20% drop in deployments would reduce the fleet to 3,727 floats in eight years. The findings indicate that the way to raise coverage is the management of deployment locations and the reduction of early losses rather than fleet size.
Keywords
Argo; Ocean observing system; Survival analysis; Weibull; Renewal model; Observation coverage; Fleet sustainability
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