Abstract
The relatively recently developed scintillometry method, with a focus on the dual-beam surface layer scintillometer (SLS), allows boundary layer atmospheric turbulence, surface sensible heat and momentum flux to be estimated in real-time. Much of the previous research using the scintillometer method has involved the large aperture scintillometer method, with only a few studies using the SLS method. The SLS method has been mainly used by agrometeorologists, hydrologists and micrometeorologists for atmospheric stability and surface energy balance studies to obtain estimates of sensible heat from which evaporation estimates representing areas of one hectare or larger are possible. Other applications include the use of the SLS method in obtaining crucial input parameters for atmospheric dispersion and turbulence models. The SLS method relies upon optical scintillation of a horizontal laser beam between transmitter and receiver for a separation distance typically between 50 and 250 m caused by refractive index inhomogeneities in the atmosphere that arise from turbulence fluctuations in air temperature and to a much lesser extent the fluctuations in water vapour pressure. Measurements of SLS beam transmission allow turbulence of the atmosphere to be determined, from which sub-hourly, real-time and in situ path-weighted fluxes of sensible heat and momentum may be calculated by application of the Monin-Obukhov similarity theory. Unlike the eddy covariance (EC) method for which corrections for flow distortion and coordinate rotation are applied, no corrections to the SLS measurements, apart from a correction for water vapour pressure, are applied. Also, path-weighted SLS estimates over the propagation path are obtained. The SLS method also offers high temporal measurement resolution and usually greater spatial coverage compared to EC, Bowen ratio energy balance, surface renewal and other sensible heat measurement methods. Applying the shortened surface energy balance, measurements of net irradiance and soil heat as well as SLS estimates of sensible heat allows path-weighted evaporation from the surface to be estimated. Research applications involving the use of the SLS method, as well as the theory on which the method is based, are presented.
Highlights
Measurements of turbulent fluxes such as sensible heat, latent energy and momentum flux, are useful to many applications in agrometeorology, hydrology, micrometeorology, environmental studies and agriculture and forestry, and the demand for reliable information of the components of the energy and water balances of land surfaces on a large spatial scale, such as watershed or river-basin scales, is increasing.1Increased demand for water, increased human impact on water resources and the potentialFor an idealised atmospheric boundary layer, which is in equilibrium, the shortened energy balance at the surface is given by the one-dimensional energy balance equation:5Rnet = LE + H + S, (1)where Rnet is the net irradiance, LE the latent energy flux density, H the sensible heat flux density and S the soil heat flux density
The advantages include38–40 the fact that flow distortion effects38 are minimised by scintillometry, due to intensity fluctuations being path-weighted in a parabolic manner with a maximum midway between the transmitter and the receiver and tapering to zero at either end of the optical path
In our work in a mixed grassland community, using simultaneous surface layer scintillometer (SLS) and eddy covariance6 (EC) measurements of H, we showed that, when using an averaging period of 2 min, the EC fluxes tended to be overestimated with the EC 60- and 120-min averages sometimes differing significantly from the SLS fluxes; depending on source characteristics and measurement height, pathaveraging up to several hundred metres for the SLS method offers possibilities for validating remote-sensing estimates of H
Summary
The relatively recently developed scintillometry method, with a focus on the dual-beam surface layer scintillometer (SLS), allows boundary layer atmospheric turbulence, surface sensible heat and momentum flux to be estimated in real-time. The SLS method has been mainly used by agrometeorologists, hydrologists and micrometeorologists for atmospheric stability and surface energy balance studies to obtain estimates of sensible heat from which evaporation estimates representing areas of one hectare or larger are possible. Measurements of SLS beam transmission allow turbulence of the atmosphere to be determined, from which sub-hourly, real-time and in situ path-weighted fluxes of sensible heat and momentum may be calculated by application of the Monin-Obukhov similarity theory. Applying the shortened surface energy balance, measurements of net irradiance and soil heat as well as SLS estimates of sensible heat allows path-weighted evaporation from the surface to be estimated. Research applications involving the use of the SLS method, as well as the theory on which the method is based, are presented
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
