Subject: Report - eTrex Venture under forest canopy
Newsgroups: sci.geo.satellite-nav
Date: Fri, 13 Apr 2001 22:53:34 -0700

I posted some info before about how my Venture
performed in both dry and wet conditions nearby
in a forested park in Vancouver.

The other day I had a chance to test it in some
forest near Squamish(this is on the road between
Vancouver and Whistler).

It was a dry, sunny day, and what I did was to
go to a series of location where I usually go in
the fall to find edible mushrooms.

The forest for the first locations was primarily
fir, logged about 70 years ago. The second area
was also primarily fir, and has been logged in the
past, but when they did so, they spaced the logging
so that they left old-growth trees every 20-50 feet.

At the time of day I was doing these tests, the satellite
display indicated that there were 9 potential satellites.
Some were low on the horizon, and the geometry was not
the best, as one area of the sky had no potentially
visible satellites at all. There were, if I remember
correctly, 3 satellites that were 'pretty much overhead'
(well within the 45 degree circle), which may have helped
with getting signals through the canopy.

The best I got, while under the canopy and trying to
set a waypoint, was 5 signals, and reported accuracy
of 8 metres. The worst was 3 signals, and 13m accuracy.
Typical was 3 or 4 signals, with 10-11m accuracy.

I tried setting a waypoint at 7 specific locations
where I always return each year because I know that
mushrooms grow in those spots. In each case, I was
able to get enough signals to establish a waypoint
at exactly the spot I wanted.

I had the tracklog feature on during my walking from
location to location, and was keeping an eye on the
satellite display while walking.

There were a few times when it reported a loss of
signal, but in each case I found that if I moved
a short distance(less than 20 feet) to where I though
that the built-in antenna might get a better signal
through the forest canopy, the signal was re-acquired,
typically within 30 seconds, although sometimes to get
at least 3 signals, I had to either move around a bit,
or change the direction the Venture was pointing.

As a tip, I noticed that when there was a loss of signal,
moving to the closest spot where the sunshine was reaching
the forest floor often enabled the signals to be received.