Quantitative analysis on the seabed terrain complexity of submarine canyons of the South China Sea continental slope

Terrain complexity index is a comprehensive index to the degree of terrain change. The bathymetric data of the Beigang Uplift area on the South China Sea Continental Slope were analyzed, from which terrain relief of the study area was extracted with the increasing grid window method using Matlab software. The optimal window area was determined by the mean change-point method. Four terrain factors, including slope, terrain relief, surface cutting depth, and the coefficient of elevation variation were combined to analyze the topographic characteristics of the study area. The method of calculating integrated terrain complexity based on the bathymetric data was introduced, and a computational complexity model to analyze the terrain complexity of the study area was established. Results show that the optimal analysis window size of the terrain relief of the study area was 19×19 grids and the optimal unit area was 1.768 9 km². The northern and southern areas of the study area feature flat terrain and low terrain complexity whose complexity index is less than 2.35. Canyons of different sizes were developed in the central area with a higher level of terrain complexity whose average complexity index is more than 3.37. Among them, the central eastern region has the most developed submarine canyons, with a terrain complexity index of 7.77. The quantitative analysis results of the topographic complexity of the study area show a good positive correlation with the intensity of sea erosion, providing an important reference for the systematic study on the morphology and evolution of submarine canyons in the South China Sea and for the maintenance of the safety of marine engineering facilities.