Research On GPS Marine Water Vapor Inversion And Three Dimensional Water Vapor Tomography

Ocean is the main place of water-vapor exchange, and86%of water vapor in the atmosphere comes from the ocean. Continuous, real-time and high-precision acquisition of oceanic water vapor is very important to accurately grasp the evolution of weather systems. China is an oceanic disaster-prone country. The Pacific has brought a lot of water vapor and precipitation for our country’s eastern region, also contributed to the frequent marine disasters for the coastal areas. Strengthening the monitoring of oceanic water vapor information is an important means of effective response to global climate change, also a key to the marine disaster prevention and mitigation measures.GPS meteorology provides a new ways for oceanic water vapor retrieval. Over the past20years, ground-based GPS meteorology obtained the rapid development and further application. GPS water vapor inversion method has been basically mature and perfect. All of these provide the basis and reference for marine GPS water vapor monitoring. Lacking of dense and solid GPS observation platforms at sea, there is only a buoy or ship as a carrier where the GPS receivers are set up. In the past decade, foreign professionals carried out exploratory research on GPS/PWV information retrieval using GPS data from ship or buoy which is offshore or over the open sea, and achieved some encouraging results. Thus the research and application of ground-based GPS meteorology has trended towards sea. Marine GPS water vapor remote sensing has been a lack of systematic research. GPS slant-path water vapor (SWV) information extraction and three-dimensional water vapor tomography is the research emphasis and difficulties on marine GPS water vapor retrieval. There are no relevant research results on the field at home and abroad. Therefore, oceanic GPS water vapor retrieval has become the weaknesses in GPS meteorology.GPS marine water vapor retrieval and three-dimensional water vapor tomography is researched in this thesis. A set of GPS marine water vapor retrieval technology and method is gained, and relevant data processing software is developed. Based on the research results of this thesis, continuous and high precision monitoring of oceanic water vapor information is achieved by means of GPS devices on the sea floats. It can compensate for satellite or airborne microwave remote sensing and sea sounding balloon, and provide a basis data for air-sea exchange research, forecasting and warning services for disaster ocean weather. Main contents and conclusions are as follows:(1) Precise point positioning (PPP) software development and its precision analysisBased on sequential least squares estimation method, the author develops precise point positioning software named as UNIP in cooperation with Hong Kong Polytechnic University, taking advantage of IGS precise satellite ephemeris and clock products. In the dynamic mode, relative to the high-precision double difference fixed solutions from GrafNavTM software, RMS of sailing ship-borne PPP solutions in X, Y, Z coordinates are within±2cm. Therefore, precise point positioning (PPP) technology based on dynamic mobile platform at sea can achieve centimeter-level positioning precision, and provide a good platform for high-precision oceanic GPS water vapor remote sensing.(2) Oceanic dynamic GPS precipitable water vapor (PWV) in the atmosphere estimateThis paper carries out in-depth research on oceanic dynamic GPS/PWV information extraction method, and gives out its function model and random model. Combining marine dynamic observation environment and temporal and spatial variation of oceanic water vapor information, random walk process is introduced as dynamic noise constraint of ZWD parameter, which simulates random changes of ship-borne GPS zenith wet delayed (ZWD). Then the influences of PWV retrieval precision for different random process noise constraint and cut-off elevation angle are analyzed.Based on UNIP software, the GPS/PWV information extraction module is developed. With Bohai ship-borne dynamic GPS measurements and synchronous meteorological observations, oceanic GPS/PWV information is extracted and accuracy validation of that is carried out relative to MM5model integral water vapor. Results show that oceanic ship-borne GPS/PWV is basically the same as MM5model. Using MM5mode as reference, the deviation of GPS/PWV is in3mm, and RMS is less than1.2mm.(3) Oceanic dynamic GPS slant-path water vapor (SWV) estimatesThe marine dynamic GPS/SWV retrieval is further researched on the basis of oceanic GPS/PWV extraction. This article has improved the existing oceanic GPS/SWV extraction algorithm, and proposed a new oceanic GPS/SWV extraction method of taking into account single-difference residual between satellites. With ship-borne dynamic GPS measurements and synchronous meteorological observations in the Bohai Sea, the oceanic GPS/SWV information is extracted and validation of improved algorithms and accuracy analysis of GPS/SWV are carried out. Results showed that the precision of oceanic dynamic GPS/SWV can achieve in millimeter range, and is basically the same as that of ground-based GPS/SWV estimation. With the proposed oceanic GPS/SWV extraction method, the deviation of GPS/SWV is in3.5millimeter relative to the MM5model integral water vapor, and accordingly its RMS is1.2millimeter. Compared with traditional "non-difference residual method", the accuracy of GPS/SWV extraction can improve about1millimeter.(4) Algorithm research and software development of three-dimensional GPS water vapor tomographyThis paper has carried out a systematic research on GPS water vapor tomography algorithm with constraint condition. Using sequential least squares estimation and successive filtering processing with time interval, random walk process estimation method is introuduced to take into account the characteristics of water vapor change over time. In view of the lack of marine water vapor, this paper puts forward and designs the solution without prior information, which is more suitable for the construction of marine three dimensional water vapor field.Based on the above algorithms, the author developed a three-dimensional GPS water vapor tomography software named as3DTom. Algorithm validation and accuracy analysis of3DTom software is carried out using Hong Kong CORS network and radiosonde data, Bohai ship-borne dynamic GPS observation and MM5data. Results showed that:①the water vapor tomography result of the2nd solution with low-precision priori information constraints is relatively poor, and appears the larger deviations in the main levels of water vapor distribution (1～4km). However the1st solution with high-precision priori information constraints is relatively optimal in three solutions, with the closest the sounding results. The results further validate the differential impact of the precision of priori information on GPS water vapor tomography. High-precision priori information can further improve the precision of GPS water vapor tomography results.②the result of3rd solution without priori information constraints is basically the same as1st solution with high-precision priori information constraints, and superior to2nd solution with low-precision priori information constraints. In the absence of priori information such as radiosonde and numerical weather model data, the designed solution without priori information by author can also get a more ideal result, and has more application value.(5) Research on the method of constructing three dimensional water vapor fields in Bohai SeaFor the study area in the Bohai Sea, this paper explores the ideas and methods on the construction of three-dimensional GPS water vapor fields over the sea. The coastal ground-based GPS stations and oceanic dynamic ship-borne or buoy observation platforms were used to realize the continuous monitoring of water vapor over the Bohai Sea. On the basis of ground-based GPS stations along the coast, the dynamic GPS meteorological monitoring networks were formed with marine dynamic ship-borne GPS observations and HY-2column water vapor products from scanning microwave radiometer. This paper proposed a research idea on joint land, marine and air exploration of water vapor spatial distribution over the Bohai Sea. Then the technique route and schematic design are provided.The local region (120.75°E～122.0°E,37.5°N～38.25°N) in the Bohai Sea was used for test area. With the help of developed UNIP and3DTom software, GPS three dimensional water vapor tomography test was first carried out by using marine ship-borne GPS observations and coastal ground-based GPS stations. The space distribution of atmospheric wet refraction over the study area is obtained. Using MM5mode as reference, the precision analysis of GPS three dimensional water vapor tomography results has been carried out. Results indicate that GPS three dimensional water vapor tomography results are basic consistent with MM5estimates, and RMS of atmospheric wet refraction in each layer is superior lOmm/km, then RMS of atmospheric wet refraction in all layers is less than5mm/km. In the sparse water vapor conditions over the local region in the Bohai Sea, this paper achieved more ideal results.Using coastal ground-based GPS/PWV as reference, the precision analysis of HY-2column water vapor products from scanning microwave radiometer has been carried out for the first time in domestic. HY-2column water vapor products have good consistency with ground-based GPS/PWV, and can be used as a new source for GPS marine three dimensional water vapor tomography.