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How Argos works

The transmitter/satellite combination

For 30 years, the Argos system has demonstrated its performance in location and data collection. It uses several relays:

Transmitters

Transmitters (an electronic circuit board inside the transmitter): these are designed to adapt to all sorts of situations, from tracking migrating birds to monitoring the polar ice caps. These very small devices may weigh as little as 20 grams. They send a message in the form of a radio signal at a frequency of 401.65 MHz with a unique identification number enabling their location to be determined. The size and shape varies according to their application.

Spacecraft's visibility ; Credits: CLS/ill. JIBE, 1998

Satellites: NOAA satellites from the US joined since 2006 by the European Metop series - serve as relays for Argos transmitters. From their polar orbits, they scan the Earth, including the poles, several times a day as they receive and store messages transmitted from the beacons.

If the sound source is stationary, the observer perceives an unvarying sound. The pitch gets higher as s/he moves closer to the source, and lower as s/he moves away. JP Penot (CNES) and B. Nicolas, ill. B Nicolas

Did you know?

The Doppler effect
We have all observed this phenomenon at one time or another, without considering its scientific or technical applications. A common example is when a passing car hoots its horn; an immobile observer perceives a variation in the sound depending on the vehicle’s position. The tone is higher pitched as it arrives and becomes lower as it moves away. This change in frequency of the sound results from the movement of the source. By analogy, we can determine the position of a transmitter by analysing the frequency of its radio waves. We call it the Doppler effect in honour of the Austrian physicist who explained the phenomenon in the 19th century.

From data collection to processing

Global receiving stations: each time a satellite passes over one of the 2 main Argos receiving stations, it downloads the content of its onboard recorder. In addition, more than 40 regional stations provide faster distribution of data.
Processing centres: these receive raw information from the receiving stations, process it, and then make it available to users, within less than 20 minutes in most cases. There are 6 users offices: Toulouse (France), Washington (United States), Lima (Peru), Tokyo (Japan), Jakarta (Indonesia) and Melbourne (Australia).