Abstract
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 at \({C_n^2 \approx 0.074 D^{5/3} \lambda^{1/3} L^{-8/3}}\), 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 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 \({C_n^2=2\times 10^{-12}{\rm m}^{-2/3}}\), which will affect many practical applications of scintillometry. The Clifford correction method, which only depends on \({C_n^2}\) 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.
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Acknowledgments
We acknowledge: funding from USGS-NIWR award number 06HQGR0187 and NMSU-WRRI contract Q01112, UC San Diego startup funding; Sevilleta National Wildlife Refuge staff for assistance with the experiment; Emily Engle and Roger Rentaria for assistance in the field; insightful comments by Henk de Bruin and an anonymous reviewer; instrumentation and access to facilities by Jan Hendrickx, New Mexico Tech.
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Open Access This is an open access article distributed under the terms of the Creative Commons Attribution Noncommercial License (https://creativecommons.org/licenses/by-nc/2.0), which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.
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Kleissl, J., Hartogensis, O.K. & Gomez, J.D. Test of Scintillometer Saturation Correction Methods Using Field Experimental Data. Boundary-Layer Meteorol 137, 493–507 (2010). https://doi.org/10.1007/s10546-010-9540-x
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DOI: https://doi.org/10.1007/s10546-010-9540-x