Basin‐scale tomography in the western Mediterranean

Abstract

An international acoustic tomography experiment had been deployed in the western Mediterranean from January to October 1994. Seven transceivers spanned the region between France, Algeria, the Balearic Islands, and Sardinia/Corsica. The basin (maximum range 600 km) was ‘‘illuminated’’ by a single HLF‐5 source, the remaining sources had a shorter range but could communicate with their neighbors. Extensive hydrographic measurements and analysis of historical data accompanied the observations, including a large‐scale survey during deployment and recovery and a 2‐weekly XBT section along the main transmission path. Some paths went along/through complicated topography, and in addition a shipboard acoustic survey was carried out to study the propagation into shallow water. All instruments remained operational for the entire period, and 6 of the 7 had 100% return of received data. The receptions show a high S/N ratio with well‐resolved arrivals that agree well with acoustic propagation predictions. The seasonal variation of the travel times appears to be a good measure of the cycle of the large‐scale heat content. The 3‐D basin‐averaged temperature is estimated to have an accuracy of 3%–4% of the seasonal amplitude. A system like this, installed with shore‐cabled instruments, should be a valuable tool for monitoring interannual and climate‐scale water mass variability.