| The sound scattering layers in the South China Sea is one of the hot research topics in recent years. Based on 4 voyages in 2009 to 2012, the vertical distribution and diurnal variation of sound scattering layers are studied with a 38 kHzship-board ADCP and a 307 kHzLADCP. The observation results of two kinds of ADCP are compared. The influence factors of sound scattering layer are studied with hydrology, biochemical and satellite altimeter data. This paper mainly includes the following four aspects:(1) There are two sound scattering layers in the South C hina Sea. The upper scattering layer distributes in 0-200 m depth, and the deep scattering layer ranges from 300 to 500 m depth. Two scattering layers show obvious diurnal variations. The upper(deep) scattering layer is weak(strong) during daytime and strong(weak) during nighttime. The vertical migration of zooplankton is consistent with the migration of scattering layers, so the migration phenomenon is perhaps caused by the vertical migration of zooplankton, and migration rate is estimated.(2) There are differences between ship-board ADCP and LADCP in observation of scattering layer, LADCP with high frequency could detect smaller scatterers, and the scattering intensity is stronger than ship-board ADCP. Ship-board ADCP could get high density data in horizontal direction, and LADCP is only used for fixed-point observation; LADCP can get high density data in the vertical direction, but ship-board ADCP is set to record data in every 16 m depth.(3) When there is a cyclonic eddy in the investigation area, the chlorophyll and silicate in 50 m water will rise, and dissolved oxygen will drop. The sound scattering layer strength is enhanced through the material transport caused by upwelling. When there is a anticyclone eddy in the investigation area, the chlorophyll and silicate in 50 m water will drop, and dissolved oxygen will rise. The sound scattering layer strength is weakened. |
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