The Uncertainty of Sensible Heat Flux Measurement over Cropland Using Large Aperture Scintillometer (LAS)
Received date: 2010-03-16
Revised date: 2010-07-14
Online published: 2010-11-10
Sensible heat flux is an important index for reflecting exchange intensity at surface-atmosphere interface. With the fast development of Eddy Covariance (EC) technique, the local sensible heat flux measurement becomes easier and more reliable. To study regional or global exchanges, the pixel-size flux measurement becomes an important and key step for up-scaling. Large Aperture Scintillometer (LAS) is the best instrument for measuring pixel-size sensible heat flux. To evaluate its accuracy and uncertainty, in this paper, the sensible heat fluxes over cropland measured by LAS and EC methods were compared, especially the reasons for errors and uncertainties were analyzed. It shows that: ①No matter in daytime or nighttime, the changing trends of the sensible heat flexes by two methods are the same. The relationship between them is very good, especially during strong exchange periods. ②There are still differences between two sensible heat fluxes. The mean abstract difference is less than 50 W/m2. Generally, when daytime flux is weak (about less than 70 W/m2), the flux measured by LAS (HLAS) is larger than that by EC (HEC), and when flux is strong, HLAS is smaller than HEC. ③Due to the heterogeneous surface, the LAS footprint will be affected by the wind speed and wind direction. Advection may induce the uncertainty for LAS sensible heat flux. In addition, based on all the variables and parameters for LAS equations, the possible sources of the uncertainty, including the uncertainty of EC method and its effect on Bowen ratio, the inaccuracy and changeable parameters (e.g. zero plane displacement and surface roughness etc.) were analyzed.
Zhu Zhilin, Sun Xiaomin, Jia Yuanyuan, Wen Xuefa, Zhang Renhua, Yuan Guofu . The Uncertainty of Sensible Heat Flux Measurement over Cropland Using Large Aperture Scintillometer (LAS)[J]. Advances in Earth Science, 2010 , 25(11) : 1199 -1207 . DOI: 10.11867/j.issn.1001-8166.2010.11.1199
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