How does satellite telemetry work?

Every satellite transmitter attached to a sea turtle has two metal contact points, called a salt-water switch. When the satellite transmitter is underwater, an electric current is able to flow between the metal contact points through the water. This tells the transmitter that is is under water so it should not send transmissions to the satellites. Every time the turtle surfaces to breathe, one or more of the metal contact points comes out of the water and the electric circuit can no longer run between the contact points. This tells the PTT that it is out of the water and to start transmitting to NOAA satellites. ARGOS receivers are carried on board NOAA polar orbiting environmental satellites providing full global coverage. The location of the transmitter is calculated and accuracy is determined as one of 5 different classes called location classes. Accuracy of ndividual locations received from the ARGOS system vary depending on the number of messages received from the transmitter, ...  more