Port authorities might want to monitor vessels that operate in national waters or in countries' exclusive economic zone to ensure they operate within their capabilities and limitations. Similarly, the vessel’s flag authority or even owner might want to monitor the ship's operation continuously. Normally, this can be done using satellites that monitor ships’ AIS signals. In case of error or if the AIS is turned off intentionally other means to monitor the ship are needed. This can be based on monitoring ships with visual wavelength satellite products, SAR satellite data or using novel instruments on satellites like monitoring of ship’s radar signal.