Sonic Layer Depth estimated from XBT temperatures and climatological salinities

Abstract Sonic layer depth (SLD) plays an important role in antisubmarine warfare in terms of identifying the shadow zones for submarine safe parking. SLD is estimated from sound velocity profiles (SVP) which is in turn obtained from temperature and salinity (T/S) profiles. Given the limited availability of salinity data in comparison to temperature, SVPs need to be obtained from alternate methods. In the present work, to make use of voluminous temperature data sets from XBT, CTD and other source for estimating SLD, we propose a method of utilizing XBT measurements and World Ocean Atlas climatological salinities to compute SVP and then extract SLD. This approach is demonstrated by utilizing T/S data from Argo floats in the Arabian Sea (40° – 80° E and 0 – 30° N). SLD is estimated from SVP obtained from Argo T/S profiles first and again by replacing the Argo salinity with climatological salinity. It is found that in more than 90% of cases, SLD matched exactly, with the root mean square deviation ranging from 3 – 12 m with an average of 7 m.