Accuracy assessment of the available geoid models in Algeria

The purpose of this paper is to evaluate available geoid models in the region of Algeria and to investigate whether the combination of geoid undulations and GPS-derived geometric heights give sufficiently accurate results to stand in for precise levelling. The geoid heights come from five different sources: three from global geopotential solutions, namely OSU91A, EGM96, and GPM98b; and two more from national gravimetric models for the area under study, computed by the Geodetic Laboratory of the National Center of Space Techniques from two sets of gravity data supplied by Bureau Gravimétrique International (BGI) and the Geophysical Exploration Technology Ltd. (GETECH). The GPS data are collected from the international TYRhenian GEOdynamical NETwork (TYRGEONET) project and local GPS surveys with baseline ranging from about 3 to 800 km. To minimise the differences between geoid and GPS/levelling undulations, we used a four-parameter transformation model. The analysis of the results shows that the differences in terms of the standard deviation between the available geoid models and GPS/levelling undulations range between ±2.2 and ±46.6 cm after the bias and tilt fit. The overall best agreement (±2.2 cm) in the experimental area is achieved when the geoid solution from BGI gravity data is used.