The Automatic Identification System（AIS）

which has been used for many years

is a communication system for maritime surveillance and navigation

and its service scope is limited to 40 nautical miles. In recent years

a new satellite based AIS has been proposed

which can provide global coverage services. However

it encounters frequency offset caused by relative satellite/ship motion. In order to solve this problem

this paper proposes a new Doppler shift estimation algorithm. The second-order matrix and the fourth-order matrix are used to extract the doppler shift from the signal

and the estimation expression is then provided. Finally

the validity of the method is verified by numerical simulation

and the superiority of the method is verified by simulation results.