Research On GPS Real-time Service (RTS) Products And Its Application

After decades of development,GNSS positioning technology is gradually mature in real-time,kinematic,low-cost,and low-precision mass positioning,as well as the high-precision,static,high-cost,and time-consuming mesurement and positioning.It is gradually developing to real-time,kinematic,loc-cost,but medium-precision(dm to sub-meter level)mass positioning.To solve the problem of GNSS positioning with the medium precision,it is necessary to provide precise satellite orbits,precise satellite clock bias,ionospheric delays and tropospheric delays corrections to the whole world via internet service in real-time.The service is named GNSS Real-Time Service(RTS).In recently years,the development of RTS products for real-time positioning has become a major task of IGS.This paper dicussed the service objects of RTS products and the contents of it,which should contains satellite orbit corrections,satellite clock corrections,ionospheric delay(and Difference Code Biac,DCB)corrections,and tropospheric delay correction.Aiming at these problems,the following contents are investigated.· Evaluation criteria system for RTS products is proposed.Evaluation of RTS products should be include two aspects: availability and accuracy.The availability of RTS products includes not only satellite availability and epoch availability,but also timeliness.More over,the accuracy includes not only the nominal accuracy of satellite orbit corrections,clock corrections,and combined products,but also the degradation over time.The paper evaluates the performance of 9 commonly used RTS products from the above criteria system and recommends two best RTS products,CLK90 and IGS03.· The problem of satellite clock common jump is solved.Because it is generally believed that the common offset of satellite clock will be absorbed by receiver clock bias,which do not affect positioning accuracy.Thus,the fusion algorithm of IGS01 is not aimed to maintain a stable time series,which causes a large number of frequent common jumps.The common jump is named datum jump.This paper fond that the frequent datum jumps can affect positioning accuracy in special cases and the switchover of reference caused the common jump.The problem can be solved from the user end or server side.For the user end,the algorithm of detection and mitigation is proposed,which eliminate the impact on positioning effectively.For the server side,a new single epoch combination algorithm is proposed,which use a continuous and stable virtual reference.Results show that two method can solve the problem of satellite common jump effectively.· Evalution method for ionospheric delay estimation algorithm is proposed.There are two commonly used algorithms,zero-difference and un-combined PPP and carrier phase smoothed code,to estimate the ionospheric delay.However,there is no evalution method to verify which is the better method on accuracy and convergency time.This paper compare the bias of slant total eletric content(STEC)derived by two algorithms,which is better than 0.1 TECU.Thus,the convergent stec can be regarded to true value.The covergency time and accuracy of two algorithms are statistically analyzed with the true.The results show that the initial convergency and accuracy of the two algorithms are similar.However,the convergence time of new satellite in data processing is obviously shorter for the PPP algorithm.Based on ionospheric delay derived from PPP algorithm,real-time global ionospheric model is established.The results show that the accuracy is 2-10 TECU.· A multi-source and heterogeneous data fusion algorithm is proposed.Based on the second-order staionary hypothesis,the semi-varogram fitting method and the weight coefficient determination algorithm.The temporal and spatial validity of GGOS ZTD and IGS ZTD are analyzed by algorithm.Real-time tropospheric model is generated by fusing the real-time IGS ZTD and forecasted GGOS ZTD.