Correlation characteristics are important for sea clutter restraint in radar image processing, which is universal in certain features for both radar and optical image. The spatial-temporal dispersion relation contained in sea clutter, which usually fits into the sum of wind friction linear item and gravity wave item, is proved effective for sea clutter restraint recently. A sea clutter restraint method for mobile searching mode observation point, which is prevalent in maritime air-borne platform, is developed from a former restraint method for shore-based stationary radar. A new extraction method for intrinsic dispersion linear item parameter of sea clutter aiming at range profile of searching mode radar system is proposed, which forms the core of the restraint method. The statistical model is founded on spatial-temporal dispersion relation and radar illumination geometry. Simulation results shows Doppler shift of measured wind linear item have a bias from the sum of sea wind and radar platform velocity. A systematic study suggests the bias could be attributed to interaction between wind friction and gravity wave item, and a rather good fitting result is obtained. CFAR detection processing for a set of experimental clutter data shows that this intrinsic dispersion extraction method formula is found to be effective in detection probability enhancement. The restraint method based on the proposed dispersion extraction method could be utilized in mobile maritime surveillance equipments.