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CoverNewton's Bulletin


Issue n. 3, January 2006   [pp. 9-18]



Application of a least square spectral filter in correcting abnormal


Okechukwu K. Nwofor and T. Chidiezie Chineke

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Abstract

The performance of a least square spectral filter in removing abnormal meteorological drifting earlier reported for a Lacoste-Romberg gravimeter is evaluated. A short (3-days) drift curve of the instrument was compared with tidal data for the location that is derived from theoretical Earth parameters before and after application of the filter. The filter was effective in remove noise registrations above 4 cycles per day in the gravimeter record. A large amplitude disparity at frequencies < 2 cycles per day between the two time series were found after application of the filter. This is attributed to temperature induced creeps in the meter spring, which resulted in phase shifts in the gravimeter series. It is concluded that a combination of “Optimum Operating Procedures” as earlier published and appropriate filtering and phase adjustments may increase gravimeter precision for measurements requiring mGal accuracy. µGal precision data would however require instruments with better temperature compensation. The procedure presented here is suggested for routine assessment of gravimeter precisions prior to field deployment, against the background of scarcity of new gravimeters for fieldwork in Nigeria.