Acoustic characterization of two atmospheric towing tanks: The case of the UPM-CEHINAV and INTA-CEHIPAR

• Comprehensive experimental comparison of the acoustic behavior of two major towing tanks (INTA-CEHIPAR and UPM-CEHINAV), focusing on their suitability for non-cavitating underwater noise studies; • Transfer function and impulse response analyses reveal how tank geometry and reverberation affect acoustic propagation, identifying key thresholds for usable frequency ranges and receiver placement. • Practical guidelines provided for effective hydroacoustic measurement setups in atmospheric towing tanks, supporting future non-cavitating noise studies. The increasing concern over underwater radiated noise (URN) from vessels and offshore wind and tidal turbines necessitates accurate experimental methods for acoustic characterization. Towing tanks, originally not designed for hydroacoustic testing, are often used to investigate noise emissions from marine propellers and turbines. However, their enclosed and reverberant nature poses significant challenges in reliably isolating and interpreting acoustic data. This study presents a comprehensive acoustic characterization of two atmospheric towing tanks: INTA-CEHIPAR (320 m x 12.5 m x 6.5 m) and UPM-CEHINAV (100 m x 3.8 m x 2.2 m). Through controlled emissions and multi-point hydrophone measurements, we quantify key parameters including transfer functions, reverberation time, absorption coefficients, and critical radius and frequency. Our results reveal substantial differences in acoustic behavior between the facilities, particularly in terms of frequency-dependent modal interference and background noise effects. The findings not only highlight the necessity of accounting for reverberant contributions but also develop guidelines for noise measurements in tank environments. These insights are essential for validating numerical simulations and advancing experimental methodologies for non-cavitating URN analysis.