Crosswinds from a Single-Aperture Scintillometer Using Spectral Techniques.pdf

Crosswinds from a Single-Aperture Scintillometer Using Spectral Techniques D ANIE ¨LLE VAN D INTHER ,O SCAR K. H ARTOGENSIS , AND A RNOLD F. M OENE Meteorology and Air Quality Group, Wageningen, Netherlands (Manuscript received 29 March 2012, in ?nal form 7 August 2012) ABSTRACT In this study, spectral techniques to obtain crosswinds from a single large-aperture scintillometer (SLAS) time series are investigated. The crosswind is de?ned as the ponent perpendicular to a path. A scintillometer obtains a path-averaged estimate of the crosswind. For certain applications this can be ad- vantageous (., monitoring crosswinds along airport runways). The essence of the spectral techniques lies in the fact that the scintillation power spectrum shifts linearly along the frequency domain as a function of the crosswind. Three different algorithms are used, which are called herein the corner frequency (CF), maximum frequency (MF), and cumulative spectrum (CS) techniques. The algorithms track the frequency shift of a characteristic point in different representations of the scintillation power spectrum. The spectrally derived pare well with sonic anemometerestimates. TheCSalgorithm obtained the best results for the crosswind pared with the sonic anemometer. However, the MF algorithm was most robust in obtaining the crosswind. Over short time intervals ( ,1 min) the crosswind can be obtained with the CS algorithm using wavelet instead of fast Fourier transformation to calculate the power scintillation spectra. 1. Introduction In this study we are interested in obtaining the ponent perpendicular to a path, the so-called cross- wind ( U ?), using scintillometer measurements. A scin- tillometer is a device that consists of a transmitter and receiver. The transmitter and receiver are placed over a path of –10 km. The transmitter emits a light beam that is refracted in the turbulent atmosphere, causing light intensity ?uctuations that are measured by the re- ceiver. The scintillome