Radar sounding of disperse streams
Atmospheric pollution by solid particles is a serious risk factor for human health. Moreover, it influences on climate change and can cause serious economical damage. More than 25% of the total air pollution comprise industrial emissions generated by fuel-burning power plants, metallurgical, and cement works. Therefore, particulate emission monitoring is an actual problem. The present dissertation is devoted to the development of remote sensing methods for estimating parameters of disperse streams (streams of solid particles which usually form particulate fraction of industrial emissions) utilizing radar technology. In order to estimate disperse stream parameters, such as mass loading, particle concentration, and particle size, theoretical methods of electromagnetic wave scattering by a spherical dielectric particle have been used; namely the approximate method of Rayleigh scattering, which is valid for particles that are much smaller than the operating wavelength of the radar, and the rigorous method – Mie theory, which allows calculating the radar cross-section (RCS) of particles in the whole range of wavelengths. Two methods of radar sounding are considered in the work: mono-frequency and double-frequency method. The mono-frequency method enables to estimate the mass loading and particle concentration, however, the method requires information about particle size and its distribution law. Applying an additional radar with a different operating frequency enables to use a concept of differential RCS which unambiguously depends on particle size for several special cases. This allows the double-frequency method to estimate the size of particles along with the mass loading and the particle concentration. For the experimental validation of the proposed measuring concepts, the mono-frequency and double-frequency radar-sensors with a bistatic antenna system have been developed and designed for operating in an air duct. Furthermore, the prototype of the mono-frequency radar with a quasioptical antenna system, which permits the transmitter and the receiver to operate with one common antenna in CW mode, has been constructed as well. Digital methods of radar signal processing, such as spectral and correlation analysis, as well as methods of statistical data processing have been utilized for the signals received by both systems. The conducted measurement results have shown that the mono-frequency method is only applicable in case of the fulfillment of the Rayleigh scattering conditions. The double-frequency method, which applies the rigorous Mie theory for estimating the RCS of particles, has shown a good reproducibility of the measurement results over a wide range of particle concentrations. The experimental study performed for the double-frequency method confirms its validity and efficiency for remote sensing of disperse streams with preliminary unknown particle size distribution law. The results shows that the developed methods of remote sensing of the disperse stream parameters by a radar can find their applications in industrial emission monitoring along with well-known optical and contact methods.
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