Argos satellite tracking:
Developed in 1978 through collaboration between the French space agency (CNES), US space agency (NASA), and the US National Oceanic and Atmospheric Administration (NOAA), the Argos satellite tracking system is now one of the most commonly used methods for tracking wildlife species across the globe as well as for taking environmental readings. In order to monitor animal movements, biologists fix small transmitters to animals which send out signals to one of the six polar orbiting Argos satellites, these satellite transmissions then allow biologists to use the Doppler shift to calculate the animals approximate location. Any additional data that is collected by the transmitter is also sent to the satellite. Currently there are 50 active terrestrial receiver stations, which take the data from the polar satellites, as well as 2 data processing centres.