“…A conductivity‐temperature‐depth (CTD) device was usually deployed to measure the temperature and electric conductivity at different depths, from which to retrieve the SSP. However, it is impractical to monitor the SSP with such devices in a vast area over long time period [5, 6]. Alternative methods include an acoustic inversion approach to monitor rapidly changing SSP [5], travel‐time data collected with an ocean acoustic tomography (OAT) technique [7] or matched field inversion [8–10].…”