The Accuracy Statistical Analysis Of CPⅢ Trigonometric Leveling

Though the specification for engineering survey of the high-speed railway states that the CPⅢ vertical control network can be established by adopting the method of the trigonometric leveling based on free-station, while the precise leveling is widely used in practical. What the accuracy level of the CPⅢ trigonometric leveling is? Whether or not the actual indices of the accuracy of the trigonometric leveling can meet the accuracy requirements for the CPⅢ vertical control network? Both of them are worth being investigated.To aimed at the above-mentioned problems, according to the actual measured data of the CPⅢ precise leveling and the CPⅢ trigonometric leveling based on free-station, which covered more than one thousand kilometer in the high-speed railway, the thesis statistically analyzed the actual indices of accuracy of the CPⅢ trigonometric leveling. Firstly, the adjustment model of CPⅢ trigonometric leveling was analyzed to provide the theoretical basis for the follow-up data computation. Secondly, all the CPⅢ control points connected to route benchmarks in the CPⅢ leveling were taken as the known points in the CPⅢ trigonometric leveling. The observed data of CPI and CPⅡ in the CPⅢ trigonometric leveling were deleted to eliminate the effect of their prism height change on the accuracy of CPⅢ trigonometric leveling. The method of the correction of the zenith-angle observations was proposed to the problem that the observed trigonometric height difference was affected by systematic error. Thereby the actual indices of the accuracy of the CPⅢ trigonometric leveling were calculated, and the statistical analysis were done for them. They included the discrepancy between the leveling elevation and trigonometric elevation at the same CPⅢ point, the height difference discrepancy at the adjacent CPⅢ points and the mean square error of the CPⅢ trigonometric elevation, before and after the correction of the zenith-angle observations. Finally, the method of the adjustment of height difference misclosure of the loop in4CPⅢ points was proposed, to get the unique elevation difference closure of the link routes, related to the network of CPⅢ trigonometric leveling. The means square error of height difference per kilometer and the elevation difference closure of the link routes were statistically analyzed by the both CPⅢ vertical survey methods. They were respectively calculated from the leveling elevation difference and the trigonometric elevation difference between the CPⅢ points spacing1km and2km, which based on the results of the constrained adjustment and the adjustment of height difference misclosure of the loop in4CP Ⅲ points. According to the statistical analysis results above-mentioned, the following conclusions were drew in this thesis. Firstly, the accuracy of the CPⅢ trigonometric leveling was influenced by systematic error, but improved after making the correction of the zenith-angle observations, whose magnitude and algebraic sign are uniform systematically to some extent. Secondly, not only the discrepancy between the leveling elevation and the trigonometric elevation at the same CPⅢ point roughly satisfied the related accuracy requirement, but the height difference discrepancy at the adjacent CPⅢ points. However, the mean square error of the CPIII trigonometric elevation didn’t meet the related accuracy requirement. Thirdly, the CPⅢ trigonometric leveling’s actual accuracy is lower than the CPIH leveling’s. Finally, the means square error of height difference per kilometer and the link routes’ the elevation difference closure of the CPⅢ trigonometric leveling, did meet the accuracy requirements of the precise leveling but not the Second Order Leveling. These conclusions maybe have some reference value to the application of the method of the CPⅢ trigonometric leveling based on free-station.