Use of the scintillometer technique over a rice paddy

Surface measurements of sensible heat flux (H) over rice paddies were made for several days using a Larger Aperture Scintillometer (LAS) operating in the near-infrared. At such wavelengths temperature (T) normally dominates refractive fluctuations and humidity (Q) fluctuations are considered insignificant. However, under conditions of low Bowen ratio β, as encountered over rice paddies the combined effects of temperature and humidity fluctuations are theoretically shown to contribute to the refractions and may be a consideration when calculating H from scintillation data. Bacause of low β and overcast skies daytime fluctuations in the refractive index structure parameter (10^-16 m^-2/3 < C_n² -14m^-2/3) were smaller on average than nocturnal values but greater than the LAS signal-to-noise figure (10^-17 m^-2/3 rms). Corrected half hourly scintillometer data for enhanced Q fluctuations did not improve the H_sc comparison to the eddy correlation H_ec which tended to underestimate for unstable but overestimate for stable conditions over a small dynamic range of data (-100-2 ). (author)