Displaced-Beam Small Aperture Scintillometer Test. Part I: The Wintex Data-Set

• Published in: Boundary-layer meteorology 2002-10, Vol.105 (1), p.129-148
• Main Authors: De Bruin, H. A. R., Meijninger, W. M. L., Smedman, Ann-Sofi, Magnusson, Mikael
• Format: Article
• Language: English
• Subjects: Errors; Kinetics; Meteorologie en Luchtkwaliteit; Meteorology; Meteorology and Air Quality; Scientific apparatus & instruments; Sensible heat; Turbulence; WIMEK; Wind speed
• ISSN: 0006-8314; 1573-1472
• DOI: 10.1023/A:1019639631711

The friction velocity (u^sub *^) and the sensible heat flux density (H) determined with a displaced-beam small aperture scintillometer (DBSAS) and a hot-film eddy correlation system are compared. Random errors in the DBSAS are relatively small, compared to scatter found with two eddy-correlation systems. Assuming that the hot-film system yields the 'true' fluxes, theDBSAS appears to overestimate u^sub *^ when u^sub *^ is less than [asymptotically =]0.2 m s^sup -1^ and to underestimate u^sub *^ at high wind speeds. This implies that the DBSAS measurements of theinner scale length of turbulence, l^sub 0^, a direct measure for the dissipation rate of kinetic turbulent energy, are biased. Possible causes for these results are discussedin detail. A correction procedure is presented to account for effects of random noise and of so-called inactive turbulence or sensor vibrations. The errors in u^sub *^ cause errors in the DBSAS measurements of the structure parameter of temperature C^sub T^^sup 2^. The derived H appears to be less sensitive to errors in l^sub 0^ and C^sub T^^sup 2^, because errors in these quantities tend to cancel out.[PUBLICATION ABSTRACT]