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System

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What's the ARGOS system?

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Illustration: Michiko Shigehara

Satellite-tracking is performed through the ARGOS system, which is a unique worldwide location and data collection system dedicated to studying and protecting the environment. ARGOS instruments are carried aboard the US National Oceanic and Atmospheric Administration's satellites (NOAA) and the European Organization for the Exploitation of Meteorological Satellite, MetOp-A. They follow a trajectory 800 km above the earth's surface at a speed of one orbit every about 100 minutes. Data received and stored by the satellites are transmitted to ground stations around the world, and then transmitted to the ARGOS Global Processing Center in the US and France. Here the information is converted into latitudinal and longitudinal position information. This information is then sent to scientists via the internet. It can take only 20-30 minutes from the time the satellite receives the signals from a transmitter to the time the location data is obtained by scientists on the ground.

Satellite transmitters called PTTs (Platform Transmitter Terminals) are secured using harnesses of Teflon-treated ribbon. Our PTTs were made by Microwave Telemetry of the USA. They weigh 9.5g and the total weight of a PTT and the harness do not exceed 2% of the buzzard’s body weight. The PTTs are solar-powered, lasting for 2-4 years of battery life. The transmission frequencies of the PTTs are set at 401.673MHz to 401.680MHz.

Location data are categorized into seven Location Classes with respect to accuracy (LC): Z (least accurate), B, A, 0, 1, 2 to 3 (most accurate). Accuracies for the least accurate location classes, A, B and Z, cannot be estimated using the ARGOS system. In general, we use LC 1-3 for data analysis, which have reported one standard deviation accuracies of 500–1,500 m, 250–500m, and <250 m, respectively (based on Argos online manual). LC 0, A, B and Z data are included only when they are spatially and temporally close to LC 1-3 location estimates.

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