Localization of Argo floats below Arctic Sea Ice

Localization of Argo floats below Arctic Sea Ice 8th Euro-Argo Science Meeting 23-25th September 2025 Heraklion, Greece Espen Storheim1 Hanne Sagen1, Lora Van Uffelen2 1 Nansen Environmental and Remote Sensing Center (NERSC) 2 University of Rhode Island (URI) CAATEX – A precursor •Moorings deployed from 2019-2020 •Transmitted 35 Hz acoustic signals across the Arctic Ocean •Acoustic thermometry. Repeat experiments from the 1990’s Acoustic sources 2600 km HiAOOS - High Arctic Ocean Observation System •Multipurpose moorings deployed from 2024 to 2026 - Acoustic thermometry - Localization of events - Positioning using active acoustics •Long-term observations •3 sound sources (synchronized) with accurate clocks •35 Hz acoustic signals transmitted every 48 hours •60 m source depth •8 minute long signals (1 min ramp-up + 7 mins) https://hiaoos.eu HiAOOS mooring network Acoustic thermometry: Inter-basin and cross basin measurements 2024 2025 517 nm (957 km) Western Arctic C. Lee et al., “Networked Autonomous Systems for Persistent Year-Round Arctic Observing – the Arctic Mobile Observing System Program” Modified SOLO-II float 25th meeting of the International Argo Steering Team https://argo.ucsd.edu/wp-content/uploads/sites/361/2024/06/AST-25_report.pdf Acoustic environment Eastern vs Western Arctic ITP data "The Ice-Tethered Profiler data were collected and made available by the Ice-Tethered Profiler Program (Toole et al., 2011; Krishfield et al., 2008) based at the Woods Hole Oceanographic Institution (https://www.whoi.edu/itp)." 35 Hz acoustic source GeoSpectrum C-BASS Diameter: 1 m Weight: 355 kg in air Max SPL: 201 dB re 1 µPa @ 1 m Packaged with batteries, D-STAR controller, power amp and pressure compensation system 70 km 176 km Observations after processing: 2019-09-11 CAATEX mooring data Depth-variation of acoustic arrivals CAATEX mooring data 2025 – Tethered float test HiAOOS2025 / Hydrophone deployed from small boat (ES) 2025 – Tethered float test 734 km 319 km 241 km Outlook •Moorings to be recovered in August/September 2026 •Actively working on funding for continuation of the mooring network •Would like to add more sources to extend coverage and increase localization accuracy Funded by the European Union Horizon Europe Programme, Grant Agreement No.101094621. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Executive Agency. Neither the European Union nor the granting authority can be held responsible for them.