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I want to improve the probable accuracy of waypoints that I collect during vegetation surveys on foot, where the canopy is overhead and continuous. My handheld receiver unit is a Garmin GPS 60 (consumer grade, position <15 metres 95% typical accuracy).

The unit accuracy is adequate for survey of open-sky areas. However, particularly in forest settings where canopy cover prevents satellite availability, will an external antenna mounted to a pole improve the accuracy? I am presuming the external antenna will see more satellites and improve accuracy that way. But is that true in practice?

The type of external antenna I have in mind are the small units that seem to be sold mainly for consumer automotive GPS use, like a Garmin GA25 MCX or Gilsson FME amplified antenna.

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    Normally having a big antenna wont improve your accuracy only your reception. If you are having trouble getting a signal from satellites low on the horizon due to trees then it might (more satellites = better location) but only if you are having problems. Does your GPS give you a 'map' of the satellites that it can 'see'? if so, are you missing some? There is a reason surveyors carry around big GPS units and aerials on sticks. – Michael Stimson May 6 '15 at 1:42
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The only thing external would do is get it a bit higher and away from any blockage of your body/ground elements when holding it. The antenna might be more sensitive/better design (re Michael's comment about reception), but since your primary obstruction is even farther overhead than that it's unlikely to make any difference. And the unit's signal processing is what it is.

Experiment - attach your unit to a pole a bit overhead and see what happens. I suspect in your use case, an external would make little or no difference. The car ones referenced are because being inside a metal box full of electrical noise is great for signal interference. My 60CSx doesn't seem to have much trouble in the evergreen forests around here (did you really mean prevents, or just limits), but then I'm usually not so concerned with accuracy that I even both to average reading to a point.

  • Good suggestion, to just atach the unit itself to a pole and see what happens. An external antenna mounted to a pole would have to deliver real benefits because walking around with a tall pole among branches would be inconvenient, and an amplified antenna would decrease battery life. – IanS May 6 '15 at 2:07
  • A SELFIE-STICK FOR A GPS! Probably best if you make the pole non-conductive (like PVC) just in case of unseen power lines or inadvertently becoming a lightning rod (unlike when carbon fibre fishing rods were first introduced; did you know that electrified overhead rail can produce sparks that jump about a foot on a humid day?). Not so much while you're in the forest but while you're testing it before going.. safety first! Like the suggestion Chris! Low-tech and cheap; I would quite like to see if that improves it any noticeable amount. – Michael Stimson May 6 '15 at 2:18

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