--- In Dan Dugan <> wrote:
>
> >> Has anyone on Naturerecordists found a GPS unit that will reliably
> >> work
> >> under the closed canopy of a tropical or subtropical rainforest?
> >
>
> -Dan
>
We have the Garmin 60Cx (SIRFIII chipset, but no compass, so cheaper) and have
used it in
Yosemite and other old growth 30m canopy conifer forest areas, sometimes in
canyon
bottoms. It is the best unit we've tried at retaining at least a 2D fix in
these challenging
settings, but sometimes you need to move 10-20 m to re-acquire a fix. I've read
that
starting the day in an open location for a few minutes where the GPS can get a
good
ephemeris download helps substantially with subsequent sites with poor coverage.
If you remain at a point for even a few minutes, these Garmin units and other
handhelds
have an easy to activate averaging mode that combines multiple fixes and you
can watch
the estimated position error decline. If you put a microSD card in them, they
can
continuously log all fixes and you can plot them after the fact with many sorts
of mapping
software.
The SIRFIII chipset for the moment seems to be the gold standard of handhelds
with
displays, but there are a couple of newer chipsets with similar sensitivity and
lower power
drain that are appearing in lower cost bluetooth or USB interface GPS with
minimal or no
display. If you want to immerse yourself in the extensive arcana of this topic,
one site for a
starting point is www.gpspassion.com. Most product innovation in this area
seems to be
going toward larger display units for use in vehicles.
Bill
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