In-situ Monitoring Of Seabed And Dynamics Characteristics Research

A set of monitoring system and methods for seabed dynamic characteristics were utilized to in-situ measure various marine elements for as long as half a year in Beibu Gulf. Taking CR800 datalogger as a core, the system carried out the acquisition, storage and output of data, which resolved the disadvantage of normal design mode highly integrated. This system is universal and can be used for different aims with a little change.The dynamic characteristics in the seabed analyzed using the in-situ data measured by LISST in Beibu Gulf. The results show that the size distribution in the sea surface is almost single, but bimodal in the middle and seafloor and the grain size increases with the increase of the depth, and is the biggest at the bottom. Grain size analysis shows that the size increases with the increase of the depth. The suspended sediment consists of sand and silt, relatively poorly sorted with positive skewness and small kurtosis values.The method using acoustic instrument to estimate suspended sediment concentration (SSC) was attempted. The results show that there is good correlation between SSC and back scattering intensity, and the linear fitting between optical and acoustic is good. But the correlation becomes worse and worse due to the bio-fouling of OBS, until at last there is no correlation between them.The roughness length is critical element to study the sediment transport and current structure. Using the current profiles measured by Acoustic Doppler Current Profiler (ADCP), the seabed roughness lengths were analyzed in different tidal cycles in the absence of the surface waves. The results show that the roughness lengths estimated from more than one tide cycle have a high correlation with r 2 larger than 0.95 and varies little ranging from 10 to 90 mm, and less fluctuating with increasing the number of data. In contrast, the roughness lengths estimated from individual current profile have a low correlation with r 2 larger than 0.2 and varies greatly ranging from 0.1 to 1600 mm. The result also shows that the roughness lengths are not sensitive to the shear velocity.