Gravity gradiometric data or gravity data transformed into vertical gradient can be efficiently processed in three dimensions for delineating density discontinuities. Model studies, performed with the combined use of maxima of analytic signal and of horizontal gradient and the Euler deconvolution techniques on the gravity field and its vertical gradient, demonstrate the superiority of the latter in locating density contrasts. Particularly in the case of interfering anomalies, where the use of gravity alone fails, the gravity gradient is able to provide useful information with satisfactory accuracy.
A method is presented that can be used for the evaluation of the value of the Earth gravity field at any defined position inside or outside an instrument used for physical or metrological experiments. After a brief presentation of the gravimeters used and the evaluation of their respective uncertainties, we describe in detail the procedure developed to determine the gravitational acceleration g at the point of interest. Finally, a realistic evaluation of the uncertainty budget shows that the method can be used in many metrological applications and especially in all experiments aiming at a new definition of the kilogram by virtual comparison of mechanical and electromagnetic power.In this paper, we denote with g the Earth gravity field or gravitational acceleration, which is the sum of all accelerations felt by a free falling body at the surface of the Earth.
Summary• All living organisms on Earth are continually exposed to diurnal variations in the gravitational tidal force due to the Sun and Moon.• Elongation of primary roots of Arabidopsis thaliana seedlings maintained at a constant temperature was monitored for periods of up to 14 d using high temporal-and spatialresolution video imaging. The time-course of the half-hourly elongation rates exhibited an oscillation which was maintained when the roots were placed in the free-running condition of continuous illumination.• Correlation between the root growth kinetics collected from seedlings initially raised under several light protocols but whose roots were subsequently in the free-running condition and the lunisolar tidal profiles enabled us to identify that the latter is the probable exogenous determinant of the rhythmic variation in root elongation rate. Similar observations and correlations using roots of Arabidopsis starch mutants suggest a central function of starch metabolism in the response to the lunisolar tide. The periodicity of the lunisolar tidal signal and the concomitant adjustments in root growth rate indicate that an exogenous timer exists for the modulation of root growth and development.• We propose that, in addition to the sensitivity to Earthly 1G gravity, which is inherent to all animals and plants, there is another type of responsiveness which is attuned to the natural diurnal variations of the lunisolar tidal force.
Cyclic leaf ascent and descent occur in synchrony and phase congruence with the lunisolar tidal force under a broad range of conditions. Digitized records of the vertical leaf movements of Arabidopsis thaliana were collected under space flight conditions in the International Space Station (ISS). Oscillations of leaf movements with periods of 45 and 90 min were found under light-adapted conditions, whereas in darkness, the periods were 45, 90, and 135 min. To demonstrate the close relationship between these oscillations and cyclical variations of the lunisolar gravitational force, we estimated the oscillations of the in-orbit lunisolar tide as they apply to the ISS, with the aid of the Etide software application. In general, in-orbit lunisolar gravitational profiles exhibited a periodicity of 45 min. Alignment of these in-orbit oscillations with the oscillations of Arabidopsis leaf movement revealed high degrees of synchrony and a congruence of phase. These data corroborate previous results which suggested a correlative relationship and a possible causal link between leaf movement rhythms obtained on ground and the rhythmic variation of the lunisolar tidal force.
The magnetic and gravity field produced by a given homogeneous source are related through Poisson's equation. Starting from this consideration, it is shown that some 2D interpretation tools, widely applied in the analysis of aeromagnetic data, can also be used for the interpretation of gravity gradiometric data (vertical gradient). This paper deals specifically with the Werner deconvolution, analytic signal and Euler's equation methods. After a short outline of the mathematical development, synthesized examples have been used to discuss the efficiency and limits of these interpretation methods. These tools could be applied directly to airborne gravity gradiometric data as well as ground gravity surveys after transformation of the Bouguer anomalies into vertical gradient anomalies. An example is given of the application of the Werner deconvolution and Euler's equation methods to a microgravity survey.
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