An Evaluation of the Nigerian Height System.

Ogunsanya, O. J (1973)

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An investigation was made into the height system in Nigeria. It was discovered that (a) all the geodetic height values so far available are provisional (b) th e height are based on an arbitrarily chosen datum referred to as the Lagos Survey Datum whose present accurate relation to the Mean sea level has not been determined, and (c) that these heights were obtained after circuit adjustment of various loops. In or der that the heights in Nigeria may be well defined, it was suggested: - (i) that the geodetic level network be referred to an accurately determined datum and (ii) that the effects of gravity values and hence gravity anomalies be considered in the compu tation of the heights. This will necessitate the observation or computation, as the case may be of gravity values of all vertical control stations in the country. An establishment of scientifically oriented tidal stations at suitable sites along the Nigeri an Coast was suggested. This, if done, will facilitate the tying of the Nigerian Level Network to the Mean Sea Level, provide a means of checking the whole level network and hence facilitate international connections. Finally, the importance of a least squ ares adjustment of the Nigerian Level Network was stressed. In addition to the theory of the least square adjustment, given in Appendix 3 of the Project Report, a level loop was adjusted by the two special forms of Least squares adjustment (the condition e quations method and the observation equations method) as an illustration. The paper is concluded with a suggestion that an absolute check be carried out on the entire framework of the Nigerian Geodetic Levelling after its completion.