Test of Scintillometer Saturation Correction Methods Using Field Experimental Data

Saturation of large aperture scintillometer (LAS) signals can result in sensible heat flux measurements that are biased low. A field study with LASs of different aperture sizes and path lengths was performed to investigate the onset of, and corrections for, signal saturation. Saturation already occurs atC2n˜ 0.074D5/3¿1/3L-8/3, where C2n is the structure parameter of the refractive index, D is the aperture size, ¿ is the wavelength, L is the transect length, which is smaller than theoretically derived saturation limits. At a transect length of 1 km, a height of 2.5 m, and aperture ˜0.15 m the correction factor exceeds 5% already at C2n= 2 × 10-12m-2/3, which will affect many practical applications of scintillometry. The Clifford correction method, which only depends on C2 n and the transect geometry, provides good saturation corrections over the range of conditions observed in our study. The saturation correction proposed by Ochs and Hill results in correction factors that are too small in large saturation regimes. An inner length scale dependence of the saturation correction factor was not observed. Thus for practical applications the Clifford correction method should be applied