Vol. 15—1961 - NorthEastern Weed Science Society

A \JINDVELOCITYANDDIRECTIONINDICATOR
FORAIRCRAFTBRUSHSPRAYINGOPERATIONS
J.M. Bennett and G.L. Parker I
Abstract
2
Aircraft application of herbicides to control brush on right-ofways
is an important part of the maintenance program of many
utilities. The most serious restriction on aircraft spraying is
suitable weather, as almost dead calm conditions are necessary
to minimize spray drift. Lack of movement of tree leaves and
absence of ripples on lakes have been the traditional indicators
of calm weather used by field personnel. These methods, although
primitive, have been satisfactory for most spray operations and
drift damage has not been serious. With the extension of aircraft
spraying to high steel tower lines, drift control has become more
difficult due to the increased altitude. At spraying heights in
excess of 100 feet, drift often occurs when there is no indication
of wind by traditional means. A convenient method of measuring
wind velocity and direction at various altitudes became essential
for satisfactory spraying of right-of-ways under high lines.
1,/ind measurement was first attempted by observing the movement of
the smoke trail produced by a signal flare fired vertically.
Some indication of wind velocity and direction was obtained,
however flares were not adequate. As~parate flare was required
for each reading and wind velocity and altitude could only be
estimated.
A hydrogen-filled tethered balloon provided the solution to the
problem. A balloon, tethered with nylon fishing line, was allowed
to rise to the desired altitude and the angle of deflection of the
line, produced by the lateral shift of the balloon, was correlated
with wind velocity. The direction of the lateral shift corresponds
to the wind direction.
Six-inch pilot balloons of the type used in meteorological studies
were used in the equipment, designed to enable direct readings of
wind velocity in the range of a to 5 miles per hour. Readings of
wind direction and balloon height are also possible.
This wind velocity and direction indicator has provided more
accurate and complete information on wind conditions than has been
available to personnel on aircraft spray operations. With this
information available, more efficient use of the limited calm
weather is possible and spray flights can be planned to reduce
spray drift to a minimum.
I Biologist and Chemist, respectively, Research Division,
The Hydro-Electric Power Commission of Ontario.
2 Abstract of a manuscript to be submitted to TJEEDS.