Gravity Measurements in Panama with the IMGC-02 Transportable Absolute Gravimeter

Abstract

The work hereafter described was designed to determine the gravity datum at the Centro Nacional de Metrologìa de Panamà CENAMEP AIP through absolute measurement of the gravity acceleration, and settle a gravity network in Panama. Twelve gravity station points were settled. Gravity data were collected with the transportable absolute ballistic gravimeter IMGC-02, operated by a team of the Istituto Nazionale di Ricerca Metrologica INRIM, in cooperation with the CENAMEP AIP and the Instituto Geográfico Nacional “Tommy Guardia” IGNTG. Establishment of the gravity net in Panama, with the highest accuracy currently obtainable, will help in the realization of primary standards and in the definition of the geodetic reference level. Moreover the gravity net may serve as reference for further detailed surveys and detection of long-term, time-dependent gravity variations

Comparison of three digital fringe signal processing methods in a ballistic free-fall absolute gravimeter

“…It was established that this bias agrees well with that predicted by the effective measurement height for the EST data. An agreement between the empirical effective height for the non-linear model (11) and the analytical effective height (10) was within 0.25 mm (one standard deviation), which is of the same level of uncertainty in determination of the effective height (4) for the ESD data [21]. Therefore, an application of the effective measurement heights (4) and (10) in this report would correspond to a standard uncertainty of less than 0.1 µGal.…”

“…At this point the iterative process is broken, and the final parameters of the heterodyne function provide the appropriate initial estimates for v 0 and g 0 within the required tolerance (figure 4(b)). Besides, the initial estimate for the fringe amplitude A 0 could be calculated as a half of the peakto-peak value of the digitized fringe signal, and the other initial parameter estimates in (11) could be set to zero. At the next step the non-linear equation ( 11) is iteratively solved, using the standard Gauss-Newton method, which is also realized by the built-in MATLAB® functions.…”

“…The non-linear model (11) ignores the vertical gravity gradient, and the undersampled fringe record contains the EST data points. To investigate the relevant effect on the computed g value, the gradient γ was included in the simulated fringe signal (1)-( 3), and the non-linear least-squares adjustment of the model (11) has been performed, following the complex heterodyne demodulation. An observed bias of the estimate ĝ0 from the given value g 0 , g γ = ĝ0 −g 0 , was converted to some specific height below the origin of the coordinate system as h γ = g γ /γ .…”

“…For the known effects of the gravity gradient and finite speed of light, it is possible to equalize this difference with the appropriate differential corrections. Controversially, these (and other) physical phenomena could be included in the fitted model (3) [2,10,11,28,29] to nullify the bias in the computed g value. However, neither model could ever be complete.…”

“…The advantages of digitizing the entire fringe signal are as follows: the imperfect electronic components are eliminated; the full information on the quality of the fringe signal is available; a noisy fringe signal is digitally filtered at the pre-processing steps; different numerical algorithms to calculate a g value can be interchangeably applied. a Initial parameter estimates are found with the two-station rise-and-fall method [11].…”