Since late 1980s there have been a series of satellite-borne microwave (MW) radiometers operated for remote sensing of water-related parameters in particular for rainfall observation among them SSMII on DMSP TMI on TRMM and AMSR-E on AQUA are well known instruments. A lot of retrieval schemes have been published for operational and research purposes. Inter-comparison of different retrieval algorithms and their products is an important task for their reliable application with enough accuracy. In this paper we will compare some algorithms for SSM/I products over West Pacific area. The methodology is mainly focusing on the comparison of retrieved hourly rain rate at the spatially and temporally collocated area statistical results and case study will be given.
A matchup dataset that contains the SSM/I measurements from F14 satellite and the columnar water vapor (CWV) radiosoundings taken in or near the China Sea was established to cover the period from April 1998 to June 1999. CWVs retrieved from two statistical and two semistatistical retrieval algorithms were compared to radiosonde CWVs using the matchup dataset. It is indicated that the root-mean-square (RMS) error of these retrievals relative to the radiosonde data ranges from 4.483 kg m-2 to 10.180 kg m-2. Three improved algorithms were developed and validated using the matchup dataset. It is demonstrated that these improved algorithms can be applied to the China Sea for retrieving CWV from the SSM/I with better accuracies relative to the four typical existing algorithms.
Although space-borne passive microwave techniques have been used in global precipitation remote sensing with preliminary success, improvement of retrieval accuracy is still an active subject. As part of Chinese National High-Tech Research and Development Program for Space Technology, an improving method for remote sensing of rainfall distribution over ocean area is investigated. In this paper, the vertical structures of cloud model are established, and the radiative transfer models are briefly introduced, also some comparison results between simulation and observation are discussed.
In order to enhance the sensing power of precipitating clouds, a dual-polarization radar is developed to be added in an active and passive microwave dual-wavelength (X/Ka band) remote sensing system. After this upgrading of dual-polarization function addition, the advanced properties of the principle of the former remote sensing system are augmented. This upgraded system becomes a new capability of synthetically sensing clouds and precipitation, and will play an important role in precipitating cloud structure studies and all kinds of major science projects concerning obtaining quantitative distribution of clouds and precipitation. The working principle, the upgrading method and the specifications of the new system and its main components are given here. An emphasis is laid on the description of the design and implementing means of the antenna-feeding unit, the control unit and data acquisition unit. A preliminary rainfall observation test of the system is also presented in this paper.
An observational method has been proposed to sample echo data with high range resolutions using a ground-based meteorological radar. Utilizing this method, a quantity of rain echo data with a high range resolution of 125 m was obtained by using an X-band meteorological radar. The computation of rain nonuniformity strength using this high resolution radar data shows that the nonuniformity is significant and even in an instantaneous field of view (IFOV) of 1 km, the reflectivity excursion above 10 dB is common. The simulation of the nonuniform beam filling (NUBF) error of the path-averaged rainrate derived from the path-integrated attenuation measured by the spaceborne radar has been also implemented using this data. The results show that the rainrate encounters mainly underestimation and cannot be neglected, even in 0.5 km IFOV, it can reach over 50%. The correlation analyses show that the rainrate error and the true rainrate have a power relationship with some correlation, which might be used to correct this error partially. The simulation also shows that it is very important to use the high resolution data in studying the NUBF error of the next generation spaceborne radar with a higher across beam resolution (e.g. below 3 km).
Rainfall distribution over global and regional scales pays important role in research and application for climate change and global water cycle within the ocean-land- atmosphere system. Satellite-borne microwave (MW) radiometry, such as DMSP's SSM/I has been proved as a powerful tool for global rainfall estimation. Although its success in revealing global pattern and annual variation of global rainfall distribution, there is still big discrepancy in the accuracy and correlation of retrieval rainfall to real rainfall. For the improvement of retrieval accuracy, we still need to investigate the relationship between MW radiometry and rainfall rate through basic radiative transfer simulation of different precipitating cloud models. In this paper the primary analysis of the simulation is given, emphasizing the difference of the simulation results and their function to the remote sensing accuracy.
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