Author: Ekpoikong Edidiong Eugene
Department: Surveying and Geoinformatics
Affiliation: Nnamdi Azikiwe University Awka

A geodetic control network should be carefully designed, constructed, observed, adjusted, analyzed and maintained in order for it to provide a full lifetime of useful control. Complex and very precise geodetic networks may require expert analysis in order to realize the full accuracy and precision of the surveying observations used to create them. In addition to precision analysis, reliability analysis (the detection of outliers/gross errors/blunders among the observations) has been measured using a technique pioneered by the geodesist Baarda. This work presents a research project on the analysis of the reliability of common GPS Networks using different techniques and methods. In this study, commonly used conventional methods (statistical test) and the redundancy method have been applied to two (2) GPS Networks with different characteristics. The baseline components ΔX, ΔY, and ΔZ of the GPS baselines have been taken as the measurements. The GPS networks were first adjusted using the MATRIX program and latter analyzed using the ADJUST program. The conventional methods (i.e. Data Snooping and Tau Test) were applied to the networks at different significant levels (0.05, 0.01 and 0.001). In GPS networks with redundant observations, choosing the significant level as 0.001 was sufficient to realize outlier detection procedure. Working with great significant levels produced unreliable results. For the redundancy number ri, the global relative redundancy was calculated. It was seen that an adjustment that in general has low redundancy numbers will have measurement that lack sufficient checks to isolate blunders, and thus the chance for undetected blunders to exist in the measurements is high. Conversely, a high overall redundancy number enables a high level of internal measurement checking and thus there is a lower chance of accepting measurements that contain blunders. Reliability analysis proves to be an effective method for network monitoring and a useful design tool when applied to GPS geodetic control networks. It should be considered when designing GPS control networks, especially those with specific requirement and error budget.GPS device manufacturers and Least-squares Adjustment software developers should be advised to incorporate reliability analysis in their programs for effective network analysis.

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