[Rhodes22-list] Believe it or not radar story

[Mark Kaynor]

I just received this on the Tayana list and thought you lot might enjoy it -
it's an interesting read.

Mark Kaynor
R22 "Raven" 

-----Original Message-----
From: Bruce [mailto:bcp at pappalini.com] 
Sent: Saturday, February 05, 2005 8:56 AM
To: Tayana Owners Discussion List
Subject: [tayana] FW: Believe it or not radar story

Okay, I know you guys are always up for a good story.
On the Baba listserv, there has been a lot of discussion about radar.
This story came out of that. 
Enjoy.
--Bruce

-----Original Message-----
Sent: Saturday, February 05, 2005 12:15 AM
Subject: Believe it or not radar story
From: "Steven Hodge"
Date: Fri, 4 Feb 2005 07:57:47 -0800

Well, heck, ok now that my arm is twisted.   I have heard this story from 3
independent sources, on different continents in fact.   After WWII the U.S.
was returning aircraft from U.K. and Europe.  The shortest distance is a
great circle route and this typically took them right over the Greenland Ice
Sheet.  A plane got caught in a storm over the ice sheet so they forged on
ahead, confident in the fact that their newly-developed radar altimeter
would keep them well away from the surface.  Sure enough the measurements
indicated they were thousands of feet up.  

Little did they know at the time--no one knew--that the particular frequency
band used for radar altimeters would penetrate cold ice (ice that is well
below the freezing point and contains no liquid water), and, in fact,
penetrates it quite well.  The reflection they were using was from the
bottom of the ice sheet, not the top.  And the ice sheet is about 3000 m
thick at the highest point of Greenland, so like I said they thought they
were thousands of feet up.

Well the storm was buffeting the plane around a lot, visibility was zilch,
and they were going right into a strong headwind.  The cockpit crew was also
exhausted from long hours of flying.  It eventually dawned on the cockpit
crew that the loadmaster was standing out in front of them in the howling
wind, giving them the "cut-throat" signal that it was ok to kill the
engines.  The cockpit crew thought they were dreaming or hallucinating, but
eventually the loadmaster was able to convince them he was for real, and
they responded and cut the engines.

The Greenland ice sheet is a huge dome, with most of the area being
essentially flat with most of the drop off near its edges.  It turns out the
pilot had unknowingly gradually flown right onto the surface of the ice
sheet, not being able to distinguish the bumpy sastrugi surface from the
wind buffetting.  The combination of extremely strong head wind, slow-flying
aircraft, and bumpy surface had in fact slowed the aircraft to a stop and
the crew out back had thought the pilot has simply decided to land and stick
out the storm, so they were merely doing what any good crew would do at that
point.

None of the stories, by the way, give any indication of what happened after
that.  I presume they were able to take off again once they realized their
situation.  However, it is known that there are aircraft buried in the
Greenland ice sheet, and, in fact, some years ago (10 or so?) there was a
big effort by some aircraft buffs to locate them and dig them out.  I do not
know the results of that.

Early ice-penetrating radars were in fact nothing but slightly modified
aircraft radar altimeters.

When liquid water is present in ice, which is the case for temperate
glaciers, the RF energy is scattered to oblivion by the cavities of liquid
water.  In technical jargon, that is because ice and water have a difference
in dielectric constant of about 80x.  It was not until the early 70's that
we (colleagues and myself) were able to develop an alternate radar technique
to allow measuring the depth of temperate ("wet") glaciers.

Steve, Panda 40 Alcyon



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