The friction velocity (u*) 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, the DBSAS appears to overestimate u* when u* is less than ≈0.2 m s-1 and to underestimate u* at high wind speeds. This implies that the DBSAS measurements of the inner scale length of turbulence, l0, a direct measure for the dissipation rate of kinetic turbulent energy, are biased. Possible causes for these results are discussed in 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* cause errors in the DBSAS measurements of the structure parameter of temperature CT2. The derived H appears to be less sensitive to errors in l0 and CT2, because errors in these quantities tend to cancel out.
DeBruin, H. A. R., & Meijninger, W. M. L. (2002). Displaced-beam small aperture scintillometer test. Part I: the WINTEX data-set. Boundary-Layer Meteorology, 105, 129-148. https://doi.org/10.1023/A:1019639631711