The present invention provides a method for validating received positional data in vehicle surveillance applications wherein vehicles transmit positional data indicating their own position to surrounding vehicles, such as an ADS-B-based aircraft surveillance application. The method involves the steps of:
receiving, with a radio direction finding antenna arrangement of a receiving unit, a signal carrying positional data indicating an alleged position of a vehicle, transmitted from a radio source;
estimating the bearing from the receiving unit to said radio source utilizing said radio direction finding antenna arrangement and the received signal;
estimating the distance between the receiving unit and the radio source based on the time of flight for a signal travelling there between at known speed;
calculating an estimated position of the radio source based on the estimated bearing and the estimated distance, and
determining a deviation value indicating the deviation/coincidence between the alleged position of a vehicle according to the received positional data and the estimated position of the radio source.