Effect of Three-Dimensional Temperature and Salinity Structure on Secci Disk Depth in South China Sea

The experiment, navigation depth and sea route of an Unmanned Undersea Vehicle (UUV) are affected by ocean current, transparency, spring layer, seawater temperature and salinity, as well as other complex hydrological environments. Based on the information ow concept, this paper investigates the cause-effect relation between the three-dimensional temperature and salinity structure and the Secci Disk Depth (SDD) by using the data of satellite remote sensing and numerical model in South China Sea, which avoids the disadvantage of the traditional correlation analysis that the causal relationship among variables cannot be accurately described. The results show that: 1) The SDD in the area around the Zhongsha Islands and offshore with lower salinity is mainly affected by the salinity of the shallow sea water because the chlorophyll concentrations are high in the seawater with higher temperature and lower salinity; 2) Seawater of the area around the Nansha Islands with high temperature and low salinity, so the SDD mainly affected by the temperature of the seawater at a depth of 20-30 meters; 3) The SDD in the area around the Xisha Islands with higher temperature and salinity is mainly affected by the temperature and salinity of the seawater at a depth of 60-70 meters; and 4) Due to the influences of temperature front and suspended sediment, the SDD around Luzon strait is mainly affected by the temperature of the seawater at a depth of 30-50 meters. Therefore, it is suggested that UUV should navigate and conduct experiment beneath the depth with maximum SDD and keep away from the depth range, where the under-water three-dimensional temperature and salinity structure has significant impact on the SDD, in order to ensure its safety, reliability and invisibility.