Argos (location)

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Argos is a satellite-based system for querying the position and measurement data of objects. For example, migratory birds receive small transmitters to track their flight routes. The COSPAS-SARSAT rescue system is a special application from Argos.

technology

Argos transmitter

The transmitters ( English platform transmitter terminals , PTT ) transmit on a carrier frequency of 401.65  MHz , on which they modulate a message of 32 bytes. The transmission time is 360–920 ms, the pauses between the repetition of the signal 45–200 s. The position is determined using the Doppler method . Satellites receive the signal and forward it to a ground station. The distance from the signal source to the satellite results from the Doppler frequency shift. The reception by several satellites and the consideration of the height profile of the earth's surface leads to a clear position determination with an accuracy better than 150 m.

Six NOAA satellites are currently receiving the Argos signals. The satellites orbit the earth on a polar trajectory at an altitude of 850 km. Your footprint (the detection area on the floor) has a diameter of approx. 5000 km. You fly over the equator approx. 6-7 times, the polar region approx. 14 times a day, so that you can locate your location after four hours at the latest.

The Metop-A satellite is equipped with an advanced Argos-3 transponder. The Argos-3 transmitters are called Platform Message Transceivers (PMT) because, unlike the PTT, they have a return channel. Its data rate is 400 bps, the uplink data rate has been increased tenfold compared to the PTT and is now 4800 bps. During a satellite overflight, they transmit data packets of 30 kBit.

operator

The NOAA (USA), NASA (USA) and CNES took Argos in 1978 together in operation. The main control center in Toulouse is operated by CLS with the participation of CNES; the second control center is located in Largo, Maryland (USA). In 1986, CNES founded the commercial offshoot CLS to market the system commercially. In addition to the three main receiving stations - Wallops Island (Virginia, USA), Fairbanks (Alaska, USA) and Lannion (France) - Argos has more than ten regional centers spread across all continents.

EUMETSAT equipped the MetOp -A satellite , which was launched in summer 2006, with third-generation Argos transponders. They increase the signal sensitivity by approx. 3 dB, the data transmission rate to 4.8 kbps, the bandwidth from 80 kHz to 110 kHz and not only allow data to be received from the PTT, but also to be transmitted to it. The Japanese ADEOS-II satellite already had these options until it failed in October 2003.

Areas of application

While in GNSS systems such as GPS the receiver on earth calculates its position by demodulating the received satellite data, the path is reversed with the Doppler method. A transmitter sends a signal to satellites, which use it to determine its position and forwards it to possible recipients via a communication network. The method allows the construction of small, inexpensive transmitters. They can weigh as little as 5 g and have an operating life of a year or more. The spatial resolution of less than 200 m is sufficient for many applications. In contrast to GNSS, the capacity is also limited.

The migration of migratory birds, herds of animals or aquatic animals can be tracked, as can the movements of ships or individual containers . Floating buoys provide information about the surface currents of the oceans and provide spatially resolved weather data such as temperature or wind speed.

PTTs, whose positions on earth have been measured exactly, serve as reference stations for determining the orbit of the satellites. The DORIS ( Doppler Orbitography and Radiopositioning Integrated by Satellite ) system measures the altitude of the satellite to within a few centimeters.

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