VHF Telemetry (triangulation)

Triangulation is the primary way that we estimate the location of a fisher. Triangulations are comprised of a series of 3 or more azimuths that provide information about where a signal (like those produced by VHF collars worn by fishers) are coming from (see illustration). Azimuths are simply our best estimate as to where the signal is coming from at any one time.

If animals are stationary and the signal is clear we should be able to get accurate and precise estimates of where the animal is located. Many things influence our ability to produce good estimates from this technique. If:

  • the animal is moving quickly,
  • we are away from the actual location of the animal,
  • the signal is bouncing off topography or
  • we take too much time between azimuths

the location we generate could be inaccurate or misleading. Triangulation is most accurate when we are very close and can take azimuths from multiple widely spaced angles relative to the animal.

Unfortunately, as with all estimates there is always some margin of error. Even though the technique is straightforward it takes a fair amount of experience to do it well. So, people that are experienced, thoughtful and hard working are invaluable for producing as many quality estimates as possible.

an illustration of a good tringulation

An illustration of a good triangulation

Taking azimuth of VHF signal.

Roger trying to locate as signal with a “rubber ducky” style antenna

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