MS Defense
One measure of atmospheric turbulence intensity is the eddy dissipation
rate, e, which is
related by the Kolmogoroff's inertial subrange hypothesis to the power spectral
density of the wind components. McCready (1964) described an airborne instrument,
which estimates e from the aircraft airspeed alone neglecting the ground
speed in the wind equation. In this talk, we evaluate the McCready technique by
comparison with e estimates using airspeed and groundspeed in the complete
three-dimensional wind equation.
The analysis confirms that groundspeed has little variance at
frequencies > 1 Hz on aircraft such as the University of Wyoming King Air
(UWKA), a light twin-engine turboprop. Thus the estimates of e using airspeed only are valid.
The Universal Indicated Turbulence System (UITS) manufactured by
Meteorology Research Incorporated (MRI) implements the McCready method. The
principle of operation of the UITS is examined and numerically simulated. A
comparison of the UITS with the full wind system on the UWKA is presented and
the limitations of the UITS discussed. It is concluded that the UITS can
provide estimates of e to within 5% of estimates from the full wind system.