Worldwide, thousands of buoys and floats are equipped with Argos transmitters,sending information via the Argos satellite system to help scientists understand andpredict climate change. Nearly 6,000 buoys of all types (drifting, moored, floating ...) roam the oceans by collecting data transmitted via Argos on currents, temperature, salinity. We absolutely had a partner to help us build our buoy but especially to provide us with the necessary hardware to send data via satellite. This equipment is veryexpensive and the possibility of using a satellite link could be achieved through theCNES and society TENUM who provided the HERA case.

History and evolution of the Argos system and the satellite lisaison

Born in 1978 in a cooperation between the Centre National d'Etudes Spatiales (CNES), the U.S. Agency for Study of Atmosphere and Ocean (NOAA) and the U.S. space agency (NASA), he was first used for safety at sea, such as monitoring of racing sailboats or locate the survivors. Today, the Argos system is primarily designed to study and protection of the environment globally.
With low power consumption and a high degree of miniaturization of the Argos can be attached to birds and mammals and operate several months.


Operation

Argos platforms automatically transmit messages that are received by satellites in low polar orbit.
A platform is a device incorporating a transmitter certified Argos. A platform periodically sends a message characterized by:

- Frequency of issue (401,650 MHz ± 30 kHz), which must be stable, because the location calculation is based on measuring the Doppler effect: this means the change in frequency of the electromagnetic wave when the source and receiver are moving relative to one another.
- The repetition period is the time interval between two consecutive shipments of message. It varies from 90 to 200 seconds depending on the use of the platform,
- The identification number of the platform,
- The data transmitted.

The transmission time of each message is less than a second.
The satellites then transfer messages to ground receiving stations. The satellite polar orbits at 850 km altitude. The period of an orbit is about 100 minutes. Each satellite views simultaneously and at any time all platforms located inside a circle with a diameter of 5000 km. With the movement of the satellite ground track of the circle forms a band 5000 km wide that winds around the Earth via the North and South Poles.

Due to the rotation of the Earth, this band shifts with each revolution of the satelliteabout 25 ° west, around the polar axis.
About 50 stations receive data sent from satellites in real time and transmit them totreatment centers.