Method for calculating visibility in fog by utilizing spectrum type of fog drop spectrum and liquid water content
A technology of liquid water content and visibility, which is applied in the field of meteorology, can solve the problems of poor visibility forecast accuracy and failure to consider the influence of visibility, and achieve the effect of reducing forecast errors
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[0076] The method for calculating the visibility in fog by using the spectral type of the droplet spectrum and the liquid water content includes the following steps, such as figure 1 :
[0077] 1) Using the existing visibility observation data and fog droplet spectrum observation data (such as the observation data in Qingdao area), taking the visibility less than 1 km as the standard, to obtain the droplet spectrum observation data during the fog occurrence period, and calculate the average fog droplet spectrum (fog The drop number concentration changes with the droplet radius, such as the mean function in Matlab can be used); then the average droplet spectrum is normalized to obtain the normalized average droplet spectrum pattern (such as figure 1 As shown, spectral types such as Junge, Deirmendian, and Gamma can be obtained through the Cftool fitting toolbox in Matlab), and then use the spectral type of the average droplet spectrum to obtain the normalized droplets correspon...
example 1
[0081] Example 1. Calculation of the visibility of the droplet spectrum of a monodisperse system (assuming that all droplets have the same droplet radius) at a certain moment.
[0082] The introduction is as follows: The measured droplet radius is r=0.2μm, the refractive index m=1.50, and the droplet number concentration is 500cm -3 , then for light with a wavelength λ of 550nm, the corresponding scale parameter α=2πr / λ is 2.28, and the scattering efficiency factor Q can be obtained as 2.19. According to the formula of extinction coefficient:
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[0084] where r i is the droplet radius, N i is the droplet number concentration, Q i is the scattering efficiency factor, so the extinction coefficient in fog is:
[0085] beta SC =π×(0.2) 2 ×500×2.19×10 -8 cm -1 =1.38×10 -6 cm -1 =0.138km -1
[0086] Thus the atmospheric visibility is Vis=3.912 / 0.138=28km. This corresponds to the meteorological line-of-sight when it is very clean.
example 2
[0087] Example 2, a polydisperse system at a certain moment (take the current common droplet spectrometer as an example, such as FM120, which can observe the droplet spectrum data of 30 continuous spectral segments, such as the spectral segments in Table 1, each spectrum segment corresponds to a droplet radius) for the calculation of the visibility of the droplet spectrum.
[0088] The introduction is as follows:
[0089] The first step is to use the mean function in Matlab to obtain the spectrum type of the average droplet spectrum according to the existing droplet spectrum observation data, and then normalize the average droplet spectrum to obtain the normalized average droplet spectrum spectral type. Then according to the number concentration calculation formula and liquid water content calculation formula:
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[0093] The radii corresponding to the 30 droplet spectral segments and the corresponding normalized number concentrations and liq...
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