Argos system

Argos is a satellite-based system to query and position data of objects. For example, migratory birds get small transmitters to track their flight routes. The rescue system COSPAS- SARSAT is a special application of Argos.

Technology

The transmitters ( platform transmitter terminals english, PTT), are on a carrier frequency of 401.65 MHz, at 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 in accordance with the Doppler method. Satellites receive the signal and pass it to a ground station on. From the Doppler frequency shift, the distance from the signal source provides to the satellite. The reception by multiple satellites and the consideration of the height profile of the soil surfaces leads to a unique positioning with an accuracy better than 150 m.

Currently received six NOAA Argos signals. The satellites orbit the Earth in a polar orbit at 850 km altitude. Your Footprint ( the detection range on the floor) has a diameter of about 5000 km. You fly over the equator about 6-7 times, the polar region about 14 times a day, so that a detection occurs after no more than four hours.

The satellite Metop- A is equipped with an advanced Argos -3 transponders. The Argos -3 Transmitter hot Platform Message Transceiver ( PMT), as they, unlike the PTT feature, via a return channel. Its data rate is 400 bps, the uplink data rate was increased tenfold over the PTT and now is 4800 bps. In a satellite overflight they transmit data packets of 30 kbit.

Operator

The NOAA (USA), NASA (USA) and CNES Argos took in 1978 in conjunction operation. Operator of the main control center in Toulouse is CLS participation of CNES, the second control center is located in Largo, Maryland (USA). In 1986, CNES commercial subsidiary CLS to the system to market commercially. Besides the three main receiving stations - Wallops Iceland (Virginia, USA), Fairbanks (Alaska, USA) and Lannion ( France) - Argos maintains more than ten regional centers, spread across all continents.

EUMETSAT equips the satellite MetOp -A, scheduled for launch in autumn 2006, with Argos transponders of the third generation. They increase the signal sensitivity by about 3 dB, the data transmission rate to 4.8 kbps, the bandwidth of 80 kHz to 110 kHz, allowing not only to receive data from the PTT, but also to transfer there. Already the Japanese satellite ADEOS - II had these opportunities to its failure in October 2003.

Areas of application

While the receiver calculates its position on the earth from the observation of the satellites in the GNSS systems such as GPS, the path with the Doppler method is reversed. A small transmitter sends a signal to satellite, the resulting determine its position and forwards via a communications network to potential recipients. The method allows the construction of small inexpensive transmitters. They weigh less than 20 grams and have an operating life of one year or more. For many applications, the spatial resolution of less than 200 m is sufficient. Also, the capacity, unlike GNSS limited.

The migration of migratory birds, herds of animals or aquatic animals can be traced, as well as the movements of ships or individual containers. Drifting buoys provide information about the surface currents of the seas and share spatially resolved meteorological data such as temperature or wind speed.

PTT whose positions were measured accurately on the earth, serve as reference stations for orbit determination of the satellites. The DORIS system (Doppler Orbitography and Radio Positioning Integrated by Satellite ) measures the altitude of the satellite just a few centimeters.