AIS-based Grid Method for Determining Ship Domains in Inland Bridge-span Waters

Ship domains are of great importance for safe navigation of ships, especially for ships navigating in inland bridge-span waters where the navigation environment is greatly different and complicated. It is essential to determine the ship domain in inland bridge-span waters to compensate the blank in this field. Aiming at contributing to this issue, this study proposes grid method in combination with Automatic Identification System (AIS) data to estimate domains for ships navigating in bridge-span waters. Firstly, the area surrounding the selected target ship is set as one with length of 3 km and width of 1 km, which is gridded into a series of basic grids. Secondly, the number of grids occupied by the nearby ships relevant to the target ship are accumulated along with the increasing time in the step of 2 minutes. The distribution of accumulated grids builds the grid density map for the target ship in the selected area. Thirdly, according to the number of the selected areas divided in the specific bridge-span waters, the equal number of grid density maps are superimposed to be defined as the grid density map for the specific bridge-span waters. Finally, the size and shape of ship domains are determined through analyzing the superimposed grid density map. It is noticeable that information of observations such as ship position are extracted from AIS. Taking the specific inland bridge-span waters, i.e. the waters of Wuhan Yangtze River from Erqi Yangtze River Bridge in Wuhan to Baishazhou Yangtze River Bridge, as case studies, the results demonstrate that the ship domains are asymmetric ellipses with different sizes. This phenomenon is aroused by the differences of ship behavior for which the setting of bridge piers and navigation regularities make sense.