Spatial Distribution of Survey Controls and Effect on Accuracy of Geometric Geoid Models (Multi-quadratic and Bicubic) in FCT, Abuja

Abstract

Spatially distributed studies may follow two broad approaches: points that are randomly located and points that are clustered or clumped together. They are discussed within a discipline described as geo-statistics. Geo-statistics is applied in order to interpolate geoid undulation (N) and hence generate through a geoid model orthometric heights from scattered/random or closely/clustered located controls. Control points are coordinated points within a primary/secondary geodetic survey network. Kriging method was adopted to produce topographical maps of the both scattered and closely scenarios. Accuracy computed revealed that standard deviation (σ) of multiquadratic and bicubic models in the study area are respectively 11cm and 14cm in lopsided control study area while over clustered distributed located controls are respectively 12cm and 15cm. Standard deviation with the lowest values among the determined geometric geoid models is at all times preferable scattered/random than closely/clumped scenario. This implies that the multiquadratic models can be applied across the entire study area with high accuracy/reliability irrespective of spatial distribution of the points. Hence, the accuracy of the models are better when the total number of points distributed within the entire study area was used than when a limited number of points within a particular part of the study area was used.

Modelling Local Gravity Anomalies from Processed Observed Gravity Measurements for Geodetic Applications

“…Dawod (1998) established a national gravity standardization network for Egypt and respectively got RMSEs of 28.55mGal and 28.38mGal for free air and Bouguer anomalies. Oluyori and Eteje (2019), since not all points can be observed or visited physically on the ground, the need for prediction/interpolation to obtain acceptable data/information is very important for decision making and analysis. In order for scientists and engineers in the above mentioned fields to carry out their studies and solve problems relating to the environment and the earth itself which require the application of gravity data in Benin City, this study has determined the absolute gravity values of some selected points, computed their local gravity anomalies and fitted an interpolation surface to enable the gravity anomaly of any point of known coordinates to be determined by interpolation/prediction within Benin City.…”