roswell

levels when the instrument is located out of doors.
For details of the use and care of theodolites.
see either the War Department publication TM-11-
423 or the U. s. Weather Bureau Circular "O".
(3) Aircraft Radio Compass
It has been found feasible to deter.mine the posi-
tion of the balloon by following the signal from a
balloon-borne transmitter. using an aircraft radio
compass as rece~ving unit. In this way it is possible
to fly along a path coward the balloon,·usually at
a much lower altitude. and. by noting the plane's
position where the compass reading is reversed. the
position of the tra-nsmitter is found. The main dis-
advantage of using this system is that aircraft is
n~eded. but there is no other method which will so
readily position the balloon over great distances
and periods of time. With this system. the limit
of tranamission time is a function of the weight of
transmitter batteries which can be carried rather
than distance. It is possible to power a trans-
mitter to supply 2 watts. for about 15 hours. using
15 pounds (7 kilograms) of batteries. Longer periods
of transmission may be achieved by intermittent opera-
tion of the transmitters or use of heavier batteries.
(4) Radar
If ground radar is available, accurate pod tioning
over a limited range can be made. It is helpful
but not strictly required to add radar targets
(corner reflectors) to the flight train for such
tracking. Using radar. the elevation angle • azimuth
angle and slant distance out are obtained, giving
a complete fix on the balloon with one set. The
maximum distance to which appropriate sets can reach
is about 65 miles; such sets are the SCR-584, the
SPM-1 and the MPS-6. V'lith good orientation and leveling
such seta have an accuracy of l.oo and about 500 feet
of slant range. Because of the limited range, radar
sets are not generally useful. Attempts to use
radar mounted atop aircraft for aeri~l observation
have been abandoned in favor of the radio compass.
B. Altitude Determination
In early attempts to utilize standard radiosonde
pressure modulators they were found to be unsatisfactory.
The Diamond-Hinman system of counting signal changes
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