Air traffic surveillance systems use both cooperative and non-cooperative techniques to locate aircraft. While non-cooperative techniques rely on the reflection of energy directed at the aircraft, cooperative techniques require the carriage of a transponder or transmitter device on board the aircraft. Systems using the signals broadcast from such transponders / transmitters are classified as a cooperative independent technology, as the ground surveillance systems derive all surveillance information from the decoded message content to determine aircraft identity and 3D position. Systems, such as ADS-B, in which the aircraft transmits it own position are classified as a cooperative dependent technology.