| China is severely affected by typhoon rain. The ordinary observations are very different to accurately measure the typhoon rain because they always happen on the ocean. So, it's very necessary to detect the typhoon rain by satellite. Spaceborne rain radar is an effective method to detect the global distribution of rain which can not only conquer the deficiencies of optical and passive microwave sensor, but also be able to directly achieve the three-dimension information of rain and provide revisal reference for passive microwave remote sensing. In order to effectively detect typhoon, heavy rain and other catastrophic weather and aim to improve the typhoon prediction and reduce typhoon damages, China is ready to load rain radar equipment on the future series satellite of FY-3. This paper intends to provide some basic basis for the selection of optimum wavebands combination through some simulations research on the rain detective ability of different frequencies.In this research,Quickbeam radar software, developed by Colorado university is used to simulate spaceborne rain radar. In order to detect the simulation ability of Quickbeam, choose the PR 2A-25 data which is most matched with the simulated typhoon on the time and compare the simulated and measured radar reflectivity factor. The results show that Quickbeam has strong simulation ability. So, Quickbeam can be used as the basic simulation software in this paper.In the study of rain detective sensitivity for different frequencies, using the hydrometer profiles of cloud water, rain, snow, etc and atmosphere parameters of hurricane BOB simulated by GCE model as the inputs of Quickbeam radar simulation software and generate radar reflectivity factor, attention, etc. Then, form a basic data volume and begin the simulation analysis. From the view of rain dynamical range in the near surface layer and attenuation, the detecting ability of five different optional radar frequencies are analyzed. They're separately 5, 10, 14, 35 and 94 GHz. The results show that the low frequency can achieve a wide dynamic range and have a small effect by attenuation; to the contrary, the high frequency can only get a small dynamic range and have a large effect by attenuation. So, in the selection of wavebands, a low frequency is necessary. What's more, 94GHz is not suitable as a frequency of the rain radar because of its severe attenuation. Furthermore, the detecting results for different rain and the sensitivity analysis on the hydrometers disturbance show high frequency is much more sensitive to weak precipitation and can make up the sensibility limitations of low frequency in the weak rain area. Finally, from the view of rain retrieval algorithm, dual-frequency can obviously improve the retrieve precision. So, it's suitable to choose dual-frequency for the rain radar of FY-3. By considering the hardware of antenna and the frequency configuration requirements of spaceborne rain radar, the optimum wavebands combination is Ku and Ka bands, Ku is benefit for detecting the strong rain while the ka is benefit for detecting the weak rain. They can used to improve the retrieve accuracy of rain.Based on the three basic conditions which should be satisfied by spaceborne radar, this paper show the advantages and disadvantages of five frequencies in the detecting of rain by using the basic data base from cloud model. This work is valuable for the design of rain radar in FY-3 which aims to detect the precipitation of typhoon and can provide some help for the rain retrieval. |
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