Improved Acoustic Tracking of RAFOS-Enabled Profiling Floats Through the New Software Package artoa4argo

Abstract

Abstract In sea ice covered polar oceans, profiling Argo floats are often unable to surface for 9 months or longer, rendering acoustic RAFOS (Ranging And Fixing Of Sound) tracking the only method to obtain unambiguous under-ice positions. Tracking RAFOS-enabled floats has historically relied on the ARTOA3 software, which had originally been tailored towards non-profiling floats in regions featuring the SOFAR (SOund Fixing And Ranging) channel with acoustic ranges of approximately 1000km. However, in sea ice covered regions, RAFOS tracking is challenged due to: (a) reduced acoustic ranges of RAFOS signals, and (b) enhanced uncertainties in float and sound source clock offsets. A new software, built on methodologies of previous ARTOA versions, called artoa4argo, has been created to overcome these issues by exploiting additional float satellite fixes, resolving ambiguous float positions when tracking with only two sources and systematically resolving float and sound source clock offsets. To gauge the performance of artoa4argo, 21 RAFOS-enabled profiling floats deployed in the Weddell Sea during 2008-2012 were tracked. These have previously been tracked in independent studies with a Kalman Smoother and a Multi-Constraint method. artoa4argo improves tracking by automating and streamlining methods. Although artoa4argo does not necessarily produce positions for every timestep, which the Kalman Smoother and Multi-Constraint methods do, whenever a track location is available, it outperforms both methods.