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The Effect of Inertial Navigation System Time Response on Airborne Turbulence Measurements

Michael TjernströmDepartment of Meteorology, Uppsala University, Uppsala, Sweden

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Patrick SamuelssonDepartment of Meteorology, Uppsala University, Uppsala, Sweden

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Abstract

Wind calculations from a radome gust probe system, in combination with a wander-angle Inertial Navigation System (INS), are used to calculate turbulence (variance and fluxes) by eddy correlation. The difference in time response between the air motion gust probe and the INS is analysed in postprocessing of in-flight data from calibration maneuvers. The effect of this difference on mean winds during accelerated maneuvers and on turbulence spectra and cospectra from low-level turbulence measurement flight legs is demonstrated.

The estimated time delay between the two systems is small for most parameters, less than 0.1 s, but is large for ground speed, about 0.1 s, and substantial for true heading, almost 0.5 s. In forced maneuvers (pitching, yawing, and turning), the effect on the calculated mean wind is significant. During typical turbulent measurement conditions, that is, straight and level flight, the effect on the winds and thus on spectra and cospectra is, however, small.

Abstract

Wind calculations from a radome gust probe system, in combination with a wander-angle Inertial Navigation System (INS), are used to calculate turbulence (variance and fluxes) by eddy correlation. The difference in time response between the air motion gust probe and the INS is analysed in postprocessing of in-flight data from calibration maneuvers. The effect of this difference on mean winds during accelerated maneuvers and on turbulence spectra and cospectra from low-level turbulence measurement flight legs is demonstrated.

The estimated time delay between the two systems is small for most parameters, less than 0.1 s, but is large for ground speed, about 0.1 s, and substantial for true heading, almost 0.5 s. In forced maneuvers (pitching, yawing, and turning), the effect on the calculated mean wind is significant. During typical turbulent measurement conditions, that is, straight and level flight, the effect on the winds and thus on spectra and cospectra is, however, small.

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