Branko MUŠIC1 / Franc DIMC2 / Radko OSREDKAR3
(1University of Ljubljana, Faculty of Arts, Department of Archaeology / 1University of Ljubljana, Faculty of Maritime Studies and Transportation, Portorož / 1University of Ljubljana, Faculty of Computer and Information Science, all Slovenia)
Some preliminary tests of various types of inexpensive single frequency Global positioning system (GPS) receivers were performed in order to assess the utility of the technique to geophysical surveying conditions. A 30 cm basic kinematical accuracy of the fixes was sought. Different sources of positioning errors are analyzed under different, realistic conditions in the field (multipath, satellite obscuration, etc) and the influence of the sampling rate and phase data processing on the relative accuracy for static and kinematical positioning analyzed. It is demonstrated that under favorable conditions a 30 cm relative uncertainty of the kinematical positioning is achievable and that under conditions where a degradation of the GPS fixes occurs during the scans, it is possible to a certain extent, by post-processing of the measurement data, to compensate for the errors and to refine the positioning results. As the GPS positioning technology, using single frequency GPS receivers, is capable of achieving this accuracy only under favorable conditions, seldom encountered in fieldwork, we have developed a hybrid positioning system, comprising of a GPS receiver and (DR) MEMS accelerometers, which is capable of augmenting the GPR positioning data in kinematical operational mode. The described system is capable of reducing the GPS trajectory orientation errors, which usually amount to ± 1 °, by 60 %, thus assuring the required accuracy. We report on the calibration of the system in some favourable test surroundings as well as on extensive Ground Penetrating Radar surveys of some actual archeological site, which has been performed with the same hybrid GPS system.