Animal Movement Research Using Phase-based Trilateration (AMRUPT)

A repository for developing and disseminating technology designed to accurately locate radio-tagged free-living animals.

• A major challenge for wildlife radio tracking is in obtaining high-accuracy position data of multiple individuals in a population. Most tracking technology used today by wildlife biologists involves the use of 1-3 researchers tracking animals while on foot (or by vehicle). This approach typically results in low-accuracy position information of just a few individuals for a relatively short period of time. A far better approach would be automated tracking of multiple individuals from a network of receivers on stationary towers. Such automated systems exist – for instance the Automated Radio Telemetry System (ARTS) at Barro Colorado Island in Panama (this systems is now defunct) – but suffer from a number of setbacks. First, most existing systems use multiple antennas to create an estimate of location based on the received strength of a signal from 3 or more receiver towers. This requires bulky and expensive receiver modules, and results in fairly imprecise location data. More recent work in automated telemetry has focused on the use of GPS technology to increase position accuracy. Unfortunately, GPS technology is still far too bulky for many small organisms and is similarly very expensive. Other efforts to create receiver networks have begun to develop the use of Time Difference of Arrival (TDOA) systems. Although these systems have great promise, they require extremely broadband signals (difficult to achieve with bare-bones transmitters), and are also limited in the degree of precision they can obtain (RF signals travel so quickly that it is highly improbable that a practical receiver network would be able to resolve animal locations beyond ~20-30 m).

• A less well-known (at least to biologists) alternative to TDOA for radio direction finding (DF) is a technique that has been used by the military for a very long time, known as Phase Interferometry for use in estimating the Angle of Arrival (AOA) of radio signals. Unlike TDOA systems, the accuracy of AOA systems scales strongly with the spatial scale of the receiver network. For instance, 10 receivers spread over 10 square kilometers might result in location estimates of +/-200 m, whereas the same number of receivers placed over 1 square kilometer might result in an accuracy of +/-20 m. Because many researchers are interested in small-scale movements of animals within populations, such a system may be extremely useful.