Uncertainty in Measurements of Wind from an NSF/NCAR Research Aircraft

The NSF/NCAR Gulfstream V research aircraft measures the motion of air relative to the Earth, or wind, using a set of sensors that provide individual measurements influencing the calculated wind vector. Three independent systems are available for such measurements, and many of the key measurements are made by redundant sensors, so they can also be checked by inter-comparison. This research aircraft typically flies at speeds faster than 200 m/s, which makes these measurements especially challenging.

This presentation will provide an analysis of uncertainty for those measurements, including estimates of the uncertainty in individual elements, calculation of the composite uncertainty, tests based on special maneuvers, discussion of correction factors that have been developed for the needed pressure measurements, and inter-comparisons among the available systems. Particular components to be included in the analysis are:

(1) a comparison to a laser air-motion sensor that detects the wind vector relative to the aircraft via the Doppler shift from aerosol particles and so provides a measurement free from calibration;

(2) a discussion of the value of circle maneuvers for detecting errors in heading or airspeed;

(3) a correction procedure based on detection and removal of Schuler-oscillation errors; and

(4) extensions to turbulence characterization and associated variance spectra.

The analysis concludes that, despite the difficulty posed by high-speed flight, for a measurement rate of 1 Hz it is possible to measure the vertical wind component with standard uncertainty of 0.1 m/s and horizontal wind components with standard uncertainty of less than 0.3 m/s.