How does Argos Doppler-derived location work?
Each time a satellite passes over a platform it collects messages transmitted by your platform and accurately measures the frequency of the received signals. Messages and measured frequencies are relayed to the Argos processing centers via ground stations. The centers then calculate the location of the platform for this given pass, accurate to within 150 meters. Argos locations are calculated by computing the Doppler shift on the transmitter signals. This is the change in frequency of a sound wave or electromagnetic wave when a transmitter and a receiver are in motion relative to each other. The classic case is the change in the sound you notice when a train approaches and moves away. Similarly, when the satellite “approaches” a transmitter, the frequency of the signal measured by the satellite receiver is higher than the actual transmit frequency, and lower when it moves away.
