How Argos system works and how the Argos data is collected?

Polar orbiting satellites collecting data: flying at an orbit of 850 km above the earth pick up the signals and store them on-board and relay them in real-time back to earth.

The satellites are on a polar orbit at an altitude of 850 km

The satellites see the North and South Poles on each orbital revolution. The orbit planes revolve around the polar axis at the same speed as the Earth around the Sun, i.e. one revolution a year. Each orbital revolution transects the equatorial plane at fixed local solar times. Therefore, each satellite passes within visibility of any given transmitter at almost the same local time each day. The time taken to complete a revolution around the Earth is approximately 100 minutes.

At any given time, each satellite simultaneously “sees” all transmitters within an approximate 5000 kilometer diameter “footprint”, or visibility circle. As the satellite proceeds in orbit, the visibility circle sweeps a 5000 kilometer swath around the Earth, covering both poles.

Due to the Earth’s rotation, the swath shifts 25° west (2800 km at the Equator) around the polar axis at each revolution. This results in overlap between successive swaths. Since overlap increases with latitude, the number of daily passes over a transmitter also increases with latitude.

At the poles, the satellites see each transmitter on every pass, approximately 14 times per day per satellite.

The period during which the satellite can receive messages from a platform is equivalent to the time during which the platform is within its visibility. On average this is 10 minutes.

Argos messages are received by the satellite simultaneously. They are stored on the onboard recorder and retransmitted to the ground each time the satellite passes over one of the three main receiving stations based on Wallops Island (Virginia, United States), Fairbanks (Alaska, United States), and Svalbard (Norway), or they are retransmitted to the ground to regional reception stations in the satellites’s field of view.