Test of Scintillometer Saturation Correction Methods Using Field Experimental Data

Abstract

Boundary Layer Meteorology manuscript No. (will be inserted by the editor) Test of scintillometer saturation correction methods using field experimental data J. Kleissl, O.K. Hartogensis, J.D. Gomez Received: Aug. 11, 2009 / Accepted: date Abstract Saturation of large aperture scintillometer (LAS) signals can result in sen- sible 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 correc- tions for signal saturation. Saturation already occurs at C n 2 ≈ 0.074D 5/3 λ 1/3 L −8/3 , where C n 2 is the structure parameter of the refractive index, D is the aperture size, λ is the wavelength, L is the transect length, which is smaller than theoretically de- rived 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 C n 2 = 2 × 10 −12 m −2/3 , which will affect many practical applications of scintillometry. The Clifford correction method, which only depends on C n 2 and 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 sat- uration correction factor was not observed. Thus for practical applications the Clifford correction method should be applied. Keywords Large aperture scintillometer · Sensible heat flux · Signal saturation · Wave propagation 1 Introduction A major challenge for the validation of surface energy balance fluxes from remote sens- ing images is the ground measurement at a scale similar to their spatial resolution. While the pixel size of daily thermal remote sensing images is on the order of km, J. Kleissl Dept. of Mechanical and Aerospace Engineering, University of California, San Diego, USA Tel.: +1-443-527-2740 E-mail: jkleissl@ucsd.edu J.D. Gomez Dept. of Earth and Environmental Sciences, New Mexico Tech, Socorro, New Mexico, USA O.K. Hartogensis Dept of Meteorology and Air Quality, Wageningen University, Wageningen, The Netherlands