Millimetre-wave radar measurement of rain and volcanic ash

Radar meteorology;Millimeter wave devices;Rain and rainfall--Measurement;Volcanic ash, tuff, etc.--Measurement

Speirs, Peter James ; Smith, Graham Murray ; Smith, Graham Murray

University:University of St Andrews

Department:Physics & Astronomy (School of)

关键词: Radar meteorology;    Millimeter wave devices;    Rain and rainfall--Measurement;    Volcanic ash, tuff, etc.--Measurement;   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/6971/PeterSpeirsPhDThesis.pdf?sequence=3&isAllowed=y

来源: DR-NTU

【 摘 要 】

This thesis presents the development of various methods for measuring rainfallrates using horizontally-pointing millimetre-wave radars. This work builds fromthe combination of a T-matrix scattering model that allows the scattering fromalmost arbitrarily pro led rotationally symmetric particles to be calculated, anddrop shape models that allow the effects of temperature and pressure on the shapeto be taken into account.Many hours of rain data have been collected with 38 and 94 GHz FMCW radars,as well as with a disdrometer and weather station. These have been used to developsingle- and dual-frequency techniques for measuring rainfall rate.A temperature, polarisation and attenuation corrected application of simplepower-law relationships between reflectivity and rainfall rate has been successfullydemonstrated at 38 GHz. However, at 94 GHz it has been found that more detailedfunctions relating reflectivity, attenuation and rainfall rate are beneficial. Areflectivity-based determination of attenuation has been adapted from the literatureand successfully applied to the 94 GHz data, improving the estimate of rainfall rateat longer ranges.The same method for estimating attenuation has also been used in a dualfrequencytechnique based on the ratio of the extinction coefficients at 38 and 94GHz, but with less success. However, a dual-frequency reflectivity ratio based approachhas been successfully developed and applied, producing good estimates ofrainfall rate, as well as reasonable estimates of two drop-size distribution parameters.Simulations of radar measurements of airborne volcanic ash have also been carriedout, demonstrating that for most reasonable measurement configurations theoptimal frequencies would typically be 35 GHz or 94 GHz, not the more commonlyused 3-10 GHz. It has also been shown that various existing millimetre-wave radarscould be used to detect ash. Finally, there is a discussion of the optimal frequenciesfor dual-frequency measurement of volcanic ash.