Research Of Low Elevation GPS Signals On Satellite Distribution And Tropospheric Delay

Low horizontal precision and high vertical precision is the current reality of Geomatics.Low altitude signals mainly affect the vertical direction positioning accuracy. For improvingthe vertical accuracy of GPS measuring, the analyzing of signal propagation characteristicsand the effect of the low elevation angles is a better breakthrough and improvement.In the field of troposphere propagation delay and satellite geometric strength factor, theeffect of low elevation satellite signal is a balanced relationship to these two aspects whichinteracts each other. At a low elevation the numbers of measurement is correspondingly bigand the RMS of vertical direction value is small, while the calculation parameters increaseand the observation noise is relatively big. To obtain satisfied accuracy, the influence ofsatellite geometric distribution and the estimation of tropospheric delay should be analyzedboth at low elevation angle.This paper begins with the analysis of impact in the troposphere estimate in terms of thelow elevation signal. Comparison with stations in the tropospheric zenith delay considers thedifference of latitude and longitude. The possibility of improving the height precision andestimation accuracy is put forward. The Chinese domestic IGS site observation data isanalyzed by use of multiple time slots and multiple spans. Under different cut-off elevationangle conditions, example experiment data is discussed with zenith delay model and mappingfunction. And the satellite constellation geometry intensity influence is calculated in differentcut-off angle to make comparative analysis. The optimum cut-off angle choice problem is letout, analyzing data capacity and effective usage at small data and low mask angle. IGS stationdata of low signal are used of different cut-off angle on summarizing of troposphericestimation and constellation GDOP effect. Data processing and analysis draw thecorresponding conclusion.Experiments adhering to one variable principle namely select the same meteorologicalparameters, tropospheric delay model and mapping function, use the same calculationsoftware and the method of parameter estimation. At different cut-off elevation angles, RMSof estimation and GDOP value are contrasted to form a comprehensive study of troposphericdelay and satellite geometry effect. The accuracy of the method and the most suitable cut-offangle are summarized, and proposals are put forward to further research on the improvementof GPS height accuracy.Through theoretical analysis and experimental study, it is concluded that: from thefollowing several aspects we can do some improvement on height accuracy: (1). Filtering effect of High precision processing software for the observation datadecreases the noise so that the data undergoes robust processing. In the estimation oftropospheric delay, low elevation angle signals contribute a lot to improve the accuracy. RMSof height positing accuracy increases with cut-off angle while the range of increasing is notobvious at low elevation angle on account of noise. The experiment generalizes a cut-offangle of5degrees or more results in increases of tropospheric delay error and elevationcalculation error with gradually increasing cut-off angle. No great difference occurs when thecutoff angle is too small.(2). in experimental satellite prediction system analysis, the low elevation angle signalefficaciously increases the number of observations to improve geometric strength. At the sametime signals near the ground sustain much noise so as not that useful to improve thepositioning accuracy of the height direction. To improve the solution quality and obtainsatisfactory positioning accuracy needs a proper cutoff angle of5degree for diminishinggeometry dilution of precision and improving strength of figure.