[TowerTalk] verticals in woods vs. in a field

[Jim Lux]

----- Original Message -----
From: "Michael Tope" <W4EF at dellroy.com>
To: "Jim Lux" <jimlux at earthlink.net>
Sent: Wednesday, September 15, 2004 8:07 PM
Subject: Re: [TowerTalk] verticals in woods vs. in a field


> It would be interesting to model up an array of lossy wires
> simulating a dense stand of trees, and then vary the lossy
> properties of the wires to see at what point they started to
> attenuate the signal.
>
> The real test would be to build a vertical in a dense stands
> of trees, measure the field strength, and then fell and clear
> all the trees over a short enough period of time such that
> confounding factors like changes in soil moisture content
> wouldn't have time to effect the results. Of course you
> would have to repeat this test for many different species
> of trees under different growing conditions and levels
> of maturity in order to draw any broad conclusions (some
> species of trees may be more lossy than others). A
> time simultaneous A/B test  comparing a vertical in the
> clear to a similar vertical in a dense stand of trees might
> be of some value, but you would have to be careful about
> controlling for ground conductivity differences between
> the two antennas.


Actually, they've done this, although not at HF (to my knowledge)...
However, there's been a lot of work at determining "ground truth" for remote
sensing measurements using VHF, UHF, and higher frequencies. google for
"BOREAS" (I think).  There's a huge amount of literature, both theoretical
analysis and field experiments, on the polarimetry and reflectivity of
various boreal forests, etc. Recently, Dr. Alina Moussessian (formerly of
JPL, now of U. Mich) was working on just this kind of thing (and bought a
huge tower trailer to support the effort; curses, the JPLARC could have used
it for FD).  There's also this guy named Dr. Charles Elachi who did some
work in the area.

In any case, if you want to attack the problem using FDTD, GTD, or any other
EM modeling technique, there's a whole lotta literature out there I
particularly like the paper from Japan where they had this tree in a pot
that they measured at a variety of frequencies in an anechoic chamber over a
period of 6 months or so, as the tree died. I don't think they intended the
tree to die, but it did, and they have this series of measurements with
successively less foliage with the tree drying out.  I picture in my mind
some egregiously underpaid grad students dragging this huge container in and
out of the chamber every week because Doctor Professor somebody got the
grant to study it.

>
> An interesting problem.
>
> 73 de Mike, W4EF..................................
>