On temporal spectra of scintillometers

Evans, Jonathan G.; De Bruin, H.A.R.. 2009 On temporal spectra of scintillometers. [Speech] In: 9th European Conference on Applications of Meteorology (ECAM), Toulouse, France, 28 September - 02 October 2009.

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Clifford (1971) derived expressions for the real and imaginary part of the temporal spectra W(f) for spherical waves propagating through the atmosphere. To a good approximation, the transmitter of a Millimeter-Wave Scintillometer (MWS) can be regarded as a point source and thus Clifford's theory is applicable to a MWS. Nieveen et al. (1998) extended Clifford's theory to large aperture scintillometers (LAS). In both cases a so called corner frequency, fc , can be defined. For frequencies smaller than fc , the real part of W(f) is approximately constant at Wplateau, whereas for f>fc , the real part of W(f) is proportional to f-8/3 for the MWS. It is noted that Wplateau is inversely proportional to the cross wind uc and that fc is proportional to uc, therefore the integral of W(f) over all f is independent of uc; however, this applies for the case where the cross wind does not vary along the path. During a field experiment carried out in mid-summer 2006 at Sheepdrove Organic Farm, UK, over mixed agricultural land use and complex topography, W(f) was measured by a 94 GHz MWS. There were contrasting cool-windy and hot-convective weather conditions during the experiment. With these data the Clifford theory will be validated.

Item Type: Publication - Conference Item (Speech)
Programmes: CEH Programmes pre-2009 publications > Water > WA02 Quantifying processes that link water quality and quantity, biota and physical environment > WA02.1 Hydrological processes
CEH Sections: Harding (to July 2011)
Date made live: 13 Oct 2010 13:27

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