Characteristics of the Submarine Topography and its Profile Type of the Coast of China

Based on the latest submarine topography data of the China 908 Project （China offshore marine environmental comprehensive investigation and assessment）,we analyzed the general China offshore submarine topographical characteristics and the factors influencing its development.The submarine topography off the coast of China follows the NW-SE trend of the land topography.The gradient of the submarine topography ranges from 0.2％ to 1.6％ with an average gradient of about 0.8％.The depth contours run mostly parallel to the coast,and extend out to sea in estuary areas.The submarine topography is dominated by the geological structure,which shows the typical characteristics of two uplifts and two subsidence events from north to south.The geological structure combined with the different sedimentary environments and complex hydrodynamic conditions produced topography that can be characterized by three types：sedimentary basins,compressionuplift,and transition form.In the sedimentary basin and compression-uplift regions,the topographical undulation is small,sediments are fine-grained,and the currents flow in a single direction,leading to bays with sedimentary plains and underwater accumulation slopes,which are of the same tectonic origin.Transition-type topography is characterized by strong undulations and mixed-size sediment particles,terraces and scarps inshore and shelf plains and erosion-deposition landforms offshore.This is a result of incomplete fault block development and repeated transgressions.In the deposition reformation regions （transition form type）,the topography has strong undulations,the sediments are coarse,tidal sand ridges are well-developed at terrigenoussupplied estuaries and convergence zones,and the Holocene sediments are thick,transformed by tides,river runoff,and currents.

Priori knowledge based a bathymetry assessment method using the sun glitter imagery:a case study of sand waves on the Taiwan Banks

High resolution optical satellite imageries containing the sun glitter,similar to synthetic aperture radar（SAR） imageries,are useful in identifying and mapping of bottom topography in shallow waters.The errors in the previous studies are corrected,and a method for mapping submarine bottom topography is developed using the sun glitter satellite imagery.The method is established on the basis of empirical description of a sand wave using an equation with two unknowns named r and k.In order to determine r and k,a ＂trial and error＂ approach is introduced and testified by a case study on the Taiwan Banks using an ASTER imagery.The results show that the inversed water depths match well with the sounding water depths.The agreement between the inversed results and the in situ measurements is about 78% by comparing 371 points.Moreover,this method has the advantage in keeping the original appearance of a sand wave,especially in positions around the sand wave crest.The fine agreement indicates that the imaging model is flexible and the approach developed is feasible.

Reconstruction of large complex sand-wave bathymetry with adaptive partitioning combining satellite imagery and sparse multi-beam data

Shallow marine sand waves are formed on the seabed and are widely distributed within tidal environments.However,the use of multibeam echo sounding(MBES)is costly to obtain the bathymetric mapping of large complex sand waves.Therefore,we propose a new method that employs a combination of multiangle sun glint images and sparse MBES data to achieve comprehensive bathymetric mapping of large and complex sand waves.This method involves estimating sea surface roughness,automatically extracting sand-wave crests,conducting adaptive subregion partitioning,estimating the water depth at auxiliary points,and generating digital bathymetric models.The method was employed in a case study of sand waves on the Taiwan Bank.Bathymetric mapping was implemented for large complex sand waves over an area spanning approximately 350 km~2 using multiangle sun glint images from the Advanced Spaceborne Thermal Emission and Reflection Radiometer and MBE S data.The results show that mapped and measured water depths were well-matched;the root-mean-square error of water depths was 1.77 m,and the relative error was 5.03%.These findings show that bathymetric mapping of large complex sand waves can be effectively conducted using the new method,and as such,the workload of MBES is reduced and efficiency is improved.