>"However, in the years since, I've become convinced that ray tracing that
>considers only a single azimuth angle has serious accuracy limitations that
>preclude its use in all but the simplest terrain."
I raised this issue back in 2019. Some reply comments:
http://lists.contesting.com/archives//html/Towertalk/2019-01/msg00140.html
Paul, W9AC
Ground reflection and diffraction at any azimuth angle can wind up at the angle
of interest. Imagine what happens when radiation intersects the slope of a hill
off your target angle. Since even a directional HF antenna has a broad forward
lobe, it illuminates lots of ground away from where it's aimed. Some of this
power can come back to haunt you.
I've cautioned HFTA users with complex terrain about the limitations of
single-azimuth ray tracing. The response is invariably, "I know it's accurate."
When asked how they know, the answer is never satisfactory. I think HFTA and TA
blind users to their shortcomings by offering fascinating and easily digestible
results.
Ray tracing involves calculating power not only for direct reflection and
diffraction, but for reflection from reflection, diffraction from reflection,
reflection from diffraction, and diffraction from diffraction. Then do it again
for higher-order cascades. This must be repeated over a dense elevation angle
set to capture everything relevant. The power of 1990s computers limited the
speed of TA. I wrote the time-consuming code in assembler to provide results in
a reasonable amount of time. Today's computers are much faster, have multiple
CPUs, and come with powerful vector instructions that can do eight
floating-point calculations simultaneously. Ray tracing over all azimuths
should be feasible today in a reasonable amount of time.
I've thought of writing a 2D (or is it 3D?) terrain analysis program.
But there's a showstopper: there's no empirical data to test it against.
Because the calculations are so complex, there's no way to ensure they are
correct without checking results against measured data for complex terrain. As
far as I know, none exists. I've searched for it and come up empty.
I've thought about what it might take to make radiation pattern measurements
over complex terrain with a drone. But it's a complicated problem with many
hidden sources of error. When I was considering this, each day I'd wake up with
a new source of error that hadn't occurred to me the day before. I think it
would be easy to get in over your head without ever knowing it. A computer
program validated with fishy data is not worth anyone's attention.
Brian
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