Global Positioning System Network Reference Control Optimization Using Dilution of Precision Variances in Gidan Kwano Area, Minna, Nigeria

Abstract

The precision of Global Positioning System (GPS) observables depends on the satellite geometry, represented by the Dilution of Precision (DOP) values, and range of errors caused by signal strength, ionospheric delay, tropospheric delay, and satellite clock offset from GPS time, multipath effects, receiver antenna phase shift, etc. One of the ways of assessing the integrity of satellite availability, positional and navigational accuracy of GPS observation is the use of dilution of precision (DOP) during field observations. This study therefore attempts to optimize GPS Network Reference Control in Gidan Kwano area of Minna, Nigeria, using pre-observation planning and post-observation DOP variances, for selecting the optimum reference point within an established survey network, for future observations and control extension in the study area. Twenty-five (25) GPS stations were observed in rapid-static mode with Leica SR20 DGPS Receivers. The estimates of the DOPs (GDOP, PDOP, HDOP, VDOP and TDOP) showed that, post-observation DOPs have mean values of 2.0, 1.8, 1.6, 0.9, and 0.9 for GDOP, PDOP, HDOP, VDOP and TDOP, respectively, which agree with the post-observation DOPs within about 80-90%. This implies that, the PDOP developed in the pre-observation planning is valid for rapid-static or kinematic surveys in the study area but less valid for a long-duration (30-minutes and above) static survey in the study area. Based on the DOPs variance analysis for each observed network point, control point GPS14 with PDOP and GDOP of 1.4 and 1.5, respectively was adjudged the optimum point as Reference for survey network observations and extension in the study area.