Assessing the positional accuracy and adequacy of the Nigerian GNSS reference network

Abstract

The availability of continuously operating reference stations (CORS) has revolutionized the realization of geodetic datum with a shift from the conventional ground survey methods to modern positioning techniques. CORS are network of reference stations that continuously provide Global Navigation Satellite Systems (GNSS) data for accurate positioning. The Nigerian GNSS reference network (NIGNET) is a network of CORS that forms an integral part of Nigeria’s geodetic infrastructure and the geodetic reference frame of Africa. As a component of the African geodetic reference frame (AFREF), it has become necessary to evaluate the positional accuracy of the data obtained from NIGNET. This study utilised the GNSS analysis and positioning software (GAPS) to determine the three-dimensional coordinates of the NIGNET stations between 2011 and 2016. The accuracy of the coordinates was evaluated against an international GNSS service (IGS) station BJCO located in Cotonou, Benin Republic. In the analysis, NIGNET showed comparable results with (BJCO) based on the computed accuracy statistics such as the standard error of mean (SEM) - BJCO (SEMX = 0.33mm; SEMY = 0.91mm; SEMZ = 0.78mm) and NIGNET (SEMX = 0.59mm; SEMY = 0.91mm; SEMZ = 0.80mm). This result signifies a high level of accuracy for NIGNET and shows that BJCO did not significantly outperform it. In conclusion, the position accuracy of NIGNET meets the international standards. However, the network adequacy is quite deficient. This poses a great challenge to the mandate of AFREF. It is therefore recommended that the Nigerian government should step up the maintenance of NIGNET in order not to compromise this mandate.