Study On The Precipitable Water Vapor And Its Variablity Over Chengdu Region Combining Ground-Base GPS And MODIS

The thermal and dynamical effect of Chengdu is very important for the weather and climate change in Sichuan. Studying atmospheric precipital water vapor (PWV) variability over Chengdu region is one of the most important ways to realize the thermal and dynamical effect, weather and climate change, as well as regional water cycle over Chengdu plain. In order to improve spatial resolution and precision of PWV over Chengdu region, in this paper, using ground-based GPS, associated with MODIS image of high spatial resolution, retrieval the PWV variability over Chengdu region.Contents of this paper including the following four aspects:Firstly, the ground-based GPS data in Chengdu (CHDU), Jianyang (JYAN), Pixian (PIXI), Qionglai (QLAI), Renshou (RENS) and Zhongjiang (ZHJI) are processed to obtain the PWV of the six stations; the PWV variability of CHDU stations covered area are analysed and compared with the Radiosonde (SONDE) data. The relationships between PWV and ground meteorology factors are studied. It shows that: the change scope of PWV in station CHDU is about 31.6mm to 62.3mm in July, 36.9mm to 62.5mm in August, and 23.1mm to 58.2mm in September; average difference between the results of ground-based GPS and the Radiosonde data on CHDU station is 045mm, with the RMS of 2.82mm, correlation coefficient of 98.27 % , a model can be fitted between ground-based GPS and SONDE, i.e.GPS = 1.018×SONDE-0.328; ground actual precipitation is well related with the change of PWV, and an abrupt increase, durative increase and abrupt change of PWV is companied with precipitation.Secondly, discussed the means of retrieving PWV using MODIS image, we procured the PWV of two-channel ratio weighted method and three-channel ratio weighted method of Chengdu region in the end. Compared the results of the two kinds weighted method to the PWV of SONDE over CHDU station, and compared the results of the two kinds weighted method, it shows that the PWV of three-channel ratio weighted method have higher dependability.Thirdly, compared the PWV of the ground-based GPS with PWV of MODIS in CHDU station. It shows that the changing trend between them are consistent with a correlation coefficient of 85.4%, but the RMS is 2.98mm, and the PWV of MODIS are low obviously, almost half of ground-based GPS results sometimes. Obviously the PWV of MODIS needs to correct, the precision of corrected PWV of MODIS increased obviously. The two are adjacent at numerical value, its relativity coefficient is 89.8%, and RMS reduce to 2.15mm.Fourthly, due to the PWV of MODIS has higher spatial resolution, its results can reflect PWV variability more detailedly. So we can associate with the PWV of ground-based GPS and MODIS to research the Chengdu region, not only increase the dependability of PWV variability, but also enhance the spatial resolution of PWV variability.In conclusion, compared with the PWV of observations data based on a few ground-based GPS stations, associate with ground-based GPS and MODIS research PWV variability, it can enhance the temporal resolution, spatial resolution, dependability, and have many excellence, such as all-weather, permanent, stabilization, low cost, and so on.