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Hi Laurence, I didnt thinkanything as crude as "chaff"was
used in ECM these days :-))
A couple of thoughts..... it was probably dropped from
30000ft altitude 10km. the effective path length for reflection off that would
be quite short around the same as VHF and microwave aircraft scatter. This has a
rangel limited to arounf 700milesmax (I think some of that isdue to tropo
bending too, which is not available at LF
The original "chaff" was cut to half wavelengths but that
was when radar was using vhf/uhf. At LF the effect would probably be one of
scattering. I think the cross-section of a jumbo even, at 136khz would be quite
small. Geo effects tend to make man's efforts look a bit puny :-))
Alan
----- Original Message -----
Sent: Monday, July 23, 2012 10:45
PM
Subject: LF: Chaff and LF
One of the most interesting weather reports this week was
from Hawaii - when a radar image showed a broad swarth of radar returns some
15 miles long and 1 mile wide gradually moving South with the prevailing wind.
I first thought it was a a weather gust front or rain squal but the weather
chappy says it was from the ongoing military exercises and they had dropped a
large amount of the chaff stuff (radar sized/reflective) and it was
causing the X band radar to show it in detail.
I was pondering -
as I sat on the beach on Maui the next day whether this form of chaff can
actually produces anomolies below the frequency engineered - as a lot of the
new type of chaff has to cover a load of GHz and MHz channelling - if the area
is large enough, as this was, and the drop density of reflective material is
large enough whether it would cause some effects as it appeared to be dropped
from 30,000ft or so...even down to LF...?
Another anomoly was
seen this morning when I was returning from Honolulu back to Anchorage - I was
approx 1200 miles South of Anchorage and a Blue glow started to appear -
firstly I thought it was just a band of Green/Blue Auroral light we get fairly
often but as we got closer it was the Notchtilucent clouds way way above
us - banded, stripes and globs of thin cloud being illuminated by the sun
which was way below our horizon and actually not even a pre glow. Now - this
isnt a normal radio thing either but on reading up on these clouds it appears
they too are radio reflective up to a point given the ions that attach to the
nulceous and given they appear to be sub-polar or polar, and mostly a summer
thing, when the temps are coldest at that altitude Im wondering if some of the
oddities we see on MF and HF are caused by these clouds
too...
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