"William W. Plummer" wrote:
Maybe someone can tell us how a hand-held GPS behaves with lots of
moisture in the air? I've been doing a lot of geocaching recently and
know for sure that trees cause outages. Maybe aircraft-certified GPS
units get around this somehow or at least flag the unreliable situation.
But how do you fly if you can't trust the GPS?

Trees block the frequencies that GPS uses. Rain and water vapor doesn't.

Presumably, if you're using the GPS for an instrument approach, you're
above treetop level, so the leaves shouldn't be blocking the signal :-)

It is certainly true that IFR certified GPS's detect and alert on
unreliable signals (that's what RAIM is all about). I still think a
handheld GPS is more accurate and reliable than a stopwatch.