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Satellite Tracking |
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The satellite transmitters (called PTTs or Platform Transmitter Terminals) used in our study are
manufactured by Microwave Telemetry Inc. The transmitters are attached using a harness of teflon ribbon that fits around the duck.
They are programmed to transmit signals for six hours
every third day. These signals are picked up by one of three NOAA
polar orbiting weather satellites. At
any given time, each satellite "sees" all transmitters within a 5000km path as it travels in its orbit.
Locations of the birds are estimated from a Doppler shift in the transmitted signal as the satellite
approaches and then moves away from the PTT. Once received the signals are relayed down to a ground
station in real time. To assign a location accuracy of less than 1000m, the
Argos processing centers
need four messages from a transmitter during a satellite pass. From there the data are processed then
sent along to us via email over a network.
Once we receive the data we further process the information using the statistical software SAS and the GIS software ARCINFO to yield location and other information that we plot on maps. As new information comes in, we compare current locations with past ones and along with other criteria decide which data points are valid. |
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