Determination of an improved Geoid Model over Zambia

Abstract

In the determination of an improved geoid over Zambia, the Modified Stokes’ formula employing the RCR technique was used. The formula combined EGM2008 data, terrestrial classical free-air gravity anomalies over Zambia, and the SRTM 3′′ DEM over Zambia which represent the long, intermediate, and short-wavelength geoid respectively. Preliminary accuracy evaluation of the proposed new geoid model termed ZG2016 at 4 GPS/Leveling stations reveal a rms error of 7.0cm compared to 69cm for the old model (ZG96: Nsombo, 1996). The higher accuracy of the new model is attributed to its use of a higher resolution GGM and DEM. Suffice to mention that EGM2008-only gave a rms error of 12.2cm when evaluated at the 4 stations. This suggests that EGM2008, though a global model, may optionally be used as a geoid model over Zambia. The evaluation of these two models using only 4 GPS/Leveling stations is not statistically acceptable. However, this is dictated by the fact that most of the established benchmarks in the country have been removed. More benchmarks will have to be found for better evaluation. If satisfactorily evaluated at more benchmarks, ZG2016 may play an important role in orthometric height determination by use of more efficient GNSS technology, thereby leading to minimisation of the use of the generally costly and labour intensive conventional leveling method in this regard. A good geoid model may also prove helpful to a number of earth-related sciences such as geology and geophysics. Key words: Geoid, RCR technique, GPS/Leveling, GNSS technology, EGM2008