Path-averaged surface fluxes determined from infrared and microwave scintillometers

Methods are needed to measure the surface fluxes of sensible (H) and latent heat (E) at large scales. A promising method is scintillometry. Over pastu re, a near-infrared scintillometer was most sensitive to temperature fluctu ations whilst a microwave scintillometer was unduly affected by both humidi ty fluctuations and correlated temperature-humidity fluctuations. Slower ch anges in path-averaged humidity caused additional signal variance and an ov erestimation of H and E. Log-amplitude spectra of the microwave scintillome ter signal showed inertial-convective subrange behavior. In combination, pa th-averaged E and H could be determined over 3 km. Independent corroborative measurements of H and E were made at the path mid point using the eddy covariance technique. For sensible heat, agreement was within 4% over a measured range 0-300 W m(-2), with a residual standard de viation of 45 W m(-2). Latent heat agreed at best to within 12% over the ra nge 0-450 W m(-2) (residual standard deviation of 94 W m(-2)) and an offset of 30 W m(-2). (C) 2001 Elsevier Science B.V. All rights reserved.