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ENCLOSURE TO ANNEX II.

Report on Aerial Observations of smoke screen 16.12.40.

(Cogry Mill, Doagh, N. Ireland).

Weather conditions at time.

Cloudless. Exceptionally good visiblity, surface wind W.S.W.

Moon 6-7 m.p.h. polar air with moderate ground inversion.

2 days after full moon rising during observations from about 15. · 40o.-

This is to be divided into two (1) Appearance of the smoke.

distinct cases a) looking towards the moon (b) looking

with moon behind.

(a) Up moon. The smoke glistened and was very similar in

appearance to the surface of the sea or to mist, but it was distinguished from mist by its being in a long streak.

(b) Down moon. It was only distinguishable from the grass

surface by the fact that the details of hedges etc.

was removed.

The smoke was more bbvious at 2000ft, and picking up the target was more difficult at 2000 ft. but this may be due to decreased time available for recognition.

(2) Appearance of Edges.

(a) Up moon. The inner ring was the most obvious except

for the ends of the outer circuit where the wind was along the line of generators. This gave a very pronounced edge to the smoke. barely visible.

The inner box was

(b) Down moon. The edges were not obvious except as the

line at which ground details became clearer.

(3) Appearance of the Target. The target was very dim when

viewed overhead and was not discernable at 450.

The water area was very difficult to pick out. The tents were never noticed but were not looked for specially.

(4) Screened Area. The screen was in the form of a long trail

with its most effective part about 1 mile down wind from the target and extending 4-5 miles down wind.

(5) The Effect of Additional Haze, and of looking through

Perspex in a Closed Aircraft.

It should be noted that these observations were made under exceptionally clear conditions in an aircraft with all windows open; so that (a) the addition of even small amounts of industrial or natural haze would have materially assisted the smoke and (b) when flying with windows closed the smoke was much less obvious as it merges well with the perspex which owing to minute surfaces scratches has scattering properties similar to the

smoke.

(Signed)

F/O N.A.C.S. RIDDELL

A.W. BREWER.

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