RADAR DETECTIBILITY OF PERSONNEL BALLOONS

• Document Type: FOIA
• Collection: FOIA Collection
• Document Number (FOIA) /ESDN (CREST): 05416086
• Release Decision: RIPPUB
• Original Classification: U
• Document Page Count: 2
• Document Creation Date: December 28, 2022
• Document Release Date: February 15, 2017
• Case Number: F-2008-00941
• Publication Date: July 10, 1956

Approved for Release: 2016/10/24 C05416086
10 July 1956
MEMORANDUM FOR: THE RECORD
SUBJECT : Radar Detectibility of Personnel Balloons
1. On 5 July 1956 the undersigned met with Dr.. Wright of the Naval
Research Lab concerning how radar worked, what its capability might be against
a personnel balloon, and how to minimize the balloon and gondola as a radar
target.
2. The return signal from radar is simply an electro-magnetic wave
reflected from the target. The intensity of the wave is a function of the
dielectric constant of the target material. A high dielectric constant
(as in matals)gives a good return signal while a low dielectric constant
(as of plastics) will tend to give a low return.
Plastic films may or may not give a good return, depending on the
thickness of the film and the wave length being used against it. A film
has two reflective surfaces and an additive or cancellation effect may result.
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The frequency of radar used depends on the results desired. For high
frequency radar (above 2500 megacycles) good resolution and short range result.
By going to low frequency (200, 400 megacycles), long range "search" radar
can be had.
3. Dr. Wright felt that a personnel balloon flying between the
altitudes of 5000 to 12000 feet would not present a particularly good radar
target. However, this would depend on the type of radar being used and the
position of the balloon relative to the radar installation.
(b)(3)
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The balloon itself would probably not present a particularly good radar
target. The gondola with its wooden base would present a better target
as would the personnel and of course any equipment.
4. Dr. Wright did not feel it would be war hwhile trying to do anything
to shield the balloon itself to minimize the radar detectibility. It might
be worthwhile however to try to reduce the return from the gondola and perhaps,
the personnel and equipment. This could be accomplished with a hair mat, which
is commercially available through B.F. Goodrich, Sponge Products Division.
For the higher frequencies (above 2000megacyc1es� the S.,X, and K bonds) matting
about 2 inches thick and weighing about 1/3 pound per square foot would reduce
the return substantially. As the frequency goes down, the required thickness
of the mat goes up - at 4o0 megacycles about 8 inches ofmat would be required.
Also, it might be possible to reduce the return from the gondola by
substituting a plastic bottm for the present wooden base. Dr. Wright suggested that
fiberglass honeycomb between 10 to 15 mil fiberglass sheets would probably
be satisfactory except at high frequencies.
5. The question of'anti-radar paints was discussed briefly. Thus
far DT. Wright has not found any thin films or coatings that effectively
deny radar target.
6. Dr. Wrightitas questioned with regard to setting up tests to determine
what the radar problem frr personnel balloons was. Two things that struck
him as important in any testing would be to get two balloons in the air
simultaneously yet separated by a mile or so - one balloon unaltered and one
modified to reduce detectibility. This would eliminate problems of atmospheric
effects, timing, etc. in comparing results. Also he recommended that,it.
possible, the balloons be tested against several�frequencies.
He mentioned that NFL has a Chesapeake Bay Annex (BA) with extensive
radar equipment. He did not know what the availability of the CDA installation
might be for our tests. The man to see for this woald be Lamont V. Blake of NFL,
7. As a passing remark, Dr. Wright mentioned that infrared, under
specialized circumstances, could conceivable be used against personnel balloons.
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