Study Of Real-Time Rapid Precise Point Positioning Based On The Reference Network

Currently, RT-PPP (Real-Time Precise Point Positioning) has been one of the key technologies to achieve real-time high-precision static or dynamic positioning globally in the future. PPP is better than DGPS (Differential GPS) in many aspects, because it has a simple observation model, have more available observations, have unrelated observations between stations which is conducive to quality control, can directly getting accurate ITRF station coordinates, receiver clock bias and absolute ZTD (Zenith Tropospheric Delay), has no distance limitations between the stations, and its time-consuming and computation is only a linear growth to the number of station. PPP have a very broad application prospects, which can be used for geodesy, reference frame maintenance, aviation dynamic measurement, precision orbit determination of LEO satellites, atmospheric research, time transfer, disaster weather forecasts, sea level changes monitoring, tsunami early warning and other fields.Real-time PPP must use real-time precise satellite clock biases (SCBs). Although IGS (International GNSS Services) has provided the IGU (IGS Ultra-rapid) SCBs, it can’t achieve the centimeter-level positioning accuracy in Real-time PPP because of the low prediction accuracy of SCBs. Therefore, the acquisition of real-time SCBs has become one of the key technologies to real-time PPP technology. In Conventional PPP model, the existence of non-integer un-differenced ambiguity parameters resulting in its positioning usually takes at least30minutes or longer convergence time to obtain centimeter-level positioning accuracy. When a cycle slip, loss of lock and other data disruption occurs, the ambiguity must be re-initialized. it can be seen, whether initialized or reinitialized are the major limitations of fast PPP.At present, many foreign and domestic countries and regions have already deployed many different sizes of global or regional reference station networks, such as CORS, IGS and EPN. CORS is used as the modern survey information infrastructure to get geospatial data, which can provide continuous, fast, reliable and high-precision kinematic positioning and atmospheric information, have been widely used in surveying and mapping, weather forecasting, atmospheric detection, traffic navigation and many other fields.The thesis focused on the existing problems of real-time rapid PPP technology based on the global or regional reference station networks, such as method of estimating real-time SCBs, the acquisition of real-time ZTD, the characteristics analysis of ZTD time series during the rainstorms and regional augemented rapid PPP. Main achievements and contributions are as follows:1) A real-time estimation method of high-precision SCBs by using the IGU prediction orbit and undifferenced ionosphere-free observations combination of the GPS reference stations network was studied. The relationship between observation amounts and real-time SCBs estimation precision, convergence speed and process time-consuming was analyzed. These relationships have a certain reference value to ensure the SCBs’ estimation accuracy and rapid solution.2) The effects of horizontal gradient and three main mapping functions on the estimation accuracy of PPP-ZTD were comparative analyzed. Results have shown that adding the horizontal gradient correction term and using appropriate mapping functions are favorable to improve PPP-ZTD precision. These conclusions has a certain practical value and significance to ensure the estimation precision of PPP-ZTD.3) A new approach for obtaining the real-time ZTD was proposed, which was based on the IGU prediction orbit and the undifference observation. The average deviations between the new real-time ZTD and IGS-ZTD are better than5mm, their RMSs are no more than6mm.4) A new approach was proposed to access the real-time PPP-ZTD time series, which can be used for the short-term predictions of heavy rainfall, based on the regional CORS network and PPP technology. Experimental analysis disclosed that the ZTD time series had a good correlation with the intensity of subsequent precipitation. These phenomenons have a certain reference value and indicating role to the short-term prediction of rainstorms.5) A new algorithm based on the augument of regional reference stations network was proposed to achieve the rapid PPP. Differ from other methods, this algorithm used the Satellite-Differenced Epoch-Differenced (SDED) technology, which can eliminate the receiver clock biases and ambiguities, avoiding the ambiguities convergence or fixed and achieving the rapid PPP.