Recently the Yangtze River Maritime Safety Administration in China used the GPS to monitor 107 passenger ships sailing in the Three Gorges enveloped by a dense fog. Since China’s Spring Festival travel season started recently, 50,000 passengers have safely traveled in and out of the Three Gorges. Recently the upper reaches of Yangtze River have been hit by extreme dense fogs. As a measure of preventing sailing accidents, maritime authorities equipped passenger ships in the river with GPS facilities free of charge. Knowing the location of each ship, the authorities can easily monitor and manage the sailing in the river. Once a ship is engaged in dangerous activities such as sailing at night, the monitor system will give an alarm to the authorities.