Effect of Differential Code Biases on the GPS CORS Network: A Case Study of Egyptian Permanent GPS Network (EPGN)

Abstract

The Global Positioning Satellite System (GPS) Continuously Operating Reference Stations (CORS) are popular and have become increasingly dense throughout the world. One of the important factors affecting the GPS accuracy is the ionosphere Total Electron Content (TEC). The hardware Differential Code Biases (DCB), inherited in both Global Positioning System satellites and receivers, influence the total electron content estimation accuracy. DCB can be estimated using GPS data themselves or during the GPS data processing.

The effect of DCB on CORS results are studied here using nine CORS stations from the Egyptian Permanent GPS Net (EPGN). Bernese software version 5.0 is used for data analysis. Three strategies are applied to the data. The first strategy is using a special MATLAB code to estimate DCB which in turn is introduced as known input in Bernese. Using Bernese itself to estimate the DCB along with the ionosphere is the second method. The third way is to totally ignore the DCB.  The three solutions are compared based on ratio of ambiguity resolutions, standard deviations, error ellipse, and closure errors.

The results indicate that the worst solution is obtained when ignoring the DCB. Both Bernese estimation and known DCB solutions are similar and gives good results. For example, the ratio of un-resolved ambiguity for baseline between Marsa-Alam and Arish is about 0.3096 for Bernese estimated DCB while it is about 0.5643 when ignoring DCB. Hence it is recommended to consider the DCB when processing GPS data for precise applications.