Gps-c-class Network, The Height Difference Is Larger Baseline Approach

Since1992,China has successfully completed the applied measurements of GPS-A, GPS-B level network that are covering the whole nation.However,there are only a few of points in a province and the distance between too longer,which are far failed to meet needs of the national economic construction and development of science and technology.There is an urgent need to establish provincial-level GPS-C level network.In China's western regions,especially mountainous areas with complex terrain, geographical location is special,and climate regional differences are significant.The establishment of GPS-C level network in these areas is different from other places.GPS-C level network point distances generally from 5 to 40 kilometers,and their geodetic differences are possible to achieve several hundred meters to the 1,000 meters.The differences of temperature,humidity,atmospheric pressure and other atmospheric conditions at the two survey stations are significant.So the path through the atmosphere of GPS signal is not exactly the same,which has resulted in the useless of model correction, and simultaneous observation difference to weaken the tropospheric delay effectively. Baseline Solution accuracy are lower.Therefore to solve the above problems is more important significance for establishing high precision GPS network in China's western region.Based on the above ideas,this article has more comprehensively analyzed the factors that affect the accuracy of the baseline and the evaluation criteria of Baseline quality. According to China's western regions,the unique geographical environment,the author has studied on the relations between geodetic difference(at both ends of the baseline)and the accuracy or quality of the baseline in GPS-C level network.At the same time,a number of simple and effective methods are suggested to solve this problem.Following are the contributions done in this paper:1)The author has analyzed the oretically why large geodetic difference or inclination angle are led to the lower baseline quality and precision in GPS-C level network.2)Repeatability is an important index to measure the accuracy of the baseline.The author developed a baseline repeatability software program(cfxPRO)with C + +.It is provided the basis for us to study on evaluation of the baseline quality in future. 3)The author has studied relationships among the baseline relative accuracy, repeatability and geodetic difference relations.Based on the analysis of experimental data we found that the quality and accuracy of the baseline are affected not only by the geodetic difference but also by the length of the baseline.Therefore,the quality and accuracy of the baseline are dominated by the inclination angle.4)Through analysis of the relationships among baseline relative accuracy, repeatability and the inclination angle,this paper has identified critical point when the geodetic difference causes "great impact" to the quality and accuracy of the baseline.The inclination angle is greater than 4.5 degrees or the geodetic difference is higher than 787 m. This is very useful to layout higher precision GPS network for the future in the mountainous areas.5)Apart from the general methods to eliminate the troposphere residual error,the paper also introduces a simple method-"add a point".Through experiments we proved that this method can reduce the troposphere residual error caused by differences in atmospheric conditions at the two ends of the baseline and improve the quality and accuracy of the baseline.6)The article summed up some methods which can increase quality and the accuracy of the baseline in GPS-C level network of China's western regions.1.In China's western regions,we have to take into account the effect of geodetic difference to the quality and the accuracy of the baseline in GPS-C level network when making optimization design,and avoid geodetic difference or inclination angle too large as far as possible.2.The selection of sites in field work should be avoided as much as possible regional differences in climate and vertical changes obvious regions,such as the deep valley,some high mountain areas and remote alpine areas.When it is necessary,the sites should be densified appropriately in these areas.3.It need obtain every site real-time measurement of meteorological data,and correct tropospheric delay by piecewise linear of software GAMIT.This can be avoided the differences of the atmospheric temperature and humidity on the impact of the quality and accuracy of the baseline as far as possible. 4.The author suggest that the observation of GPS-C level network in field should make use of operating mode of GPS based on the continuous operation base station.