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A land gravity survey was carried out in the Kinigi geothermal field, Northwest Rwanda using 184 gravity stations during August and September, 2015. The aim of the gravity survey was to understand the subsurface structure and its relation to the observed surface manifestations in the study area. The complete Bouguer Gravity anomaly was produced with a reduction density of 2.4 g/cm 3 . Bouguer anomalies ranging from −52 to −35 mGals were observed in the study area with relatively high anomalies in the east and northwest zones while low anomalies are observed in the southwest side of the studied area. A decrease of 17 mGals is observed in the southwestern part of the study area and caused by the low-density of the Tertiary rocks. Horizontal gradient, tilt angle and analytical signal methods were applied to the observed gravity data and showed that Mubona, Mpenge and Cyabararika surface springs are structurally controlled while Rubindi spring is not. The integrated results of gravity gradient interpretation methods delineated a dominant geological structure trending in the NW-SE, which is in agreement with the regional geological trend. The results of this gravity study will help aid future geothermal exploration and development in the Kinigi geothermal field.

Normalized downward continuation (NDC) method calculates the normalization on the analytical signal modulus of the downward continued field or the downward continuation of the potential field itself, which is used to obtain the edges position and buried depth information. In this study, we applied the NDC method to the edge detector defined as the combination of the directional total horizontal derivatives (DTHD) to improve the lateral resolution. The iterative downward continuation is introduced in the computation process which has a large downward continuation distance. The synthetic gravity data with and without noise are used to test the effectiveness of the new presented approach. The results show that NDC applied to the edge detector based on DTHD has a better resolution than the previous method based on the directional analytic signals, and the source edges and depth information can be obtained simultaneously. Finally, we apply the method to the gravity data acquired over the Humble Salt Dome in USA. The results show a good correspondence to the previous work results.

We compile the GOCE-only satellite model GOSG01S complete to spherical harmonic degree of 220 using Satellite Gravity Gradiometry (SGG) data and the Satellite-to-Satellite Tracking (SST) observations along the GOCE orbit based on applying a least-squares analysis. The diagonal components ( V xx , V yy , V zz ) of the gravitational gradient tensor are used to form the system of observation equations with the band-pass ARMA filter. The point-wise acceleration observations ( a x , a y , a z ) along the orbit are used to form the system of observation equations up to the maximum spherical harmonic degree/order 130. The analysis of spectral accuracy characteristics of the newly derived gravitational model GOSG01S and the existing models GOTIM04S, GODIR04S, GOSPW04S and JYY_GOCE02S based on their comparison with the ultra-high degree model EIGEN-6C2 reveals a significant consistency at the spectral window approximately between 80 and 190 due to the same period SGG data used to compile these models. The GOCE related satellite gravity models GOSG01S, GOTIM05S, GODIR05S, GOTIM04S, GODIR04S, GOSPW04S, JYY_GOCE02S, EIGEN-6C2 and EGM2008 are also validated by using GPS-leveling data in China and USA. According to the truncation at degree 200, the statistic results show that all GGMs have very similar differences at GPS-leveling points in USA, and all GOCE related gravity models have better performance than EGM2008 in China. This suggests that all these models provide much more information on the gravity field than EGM2008 in areas with low terrestrial gravity coverage. And STDs of height anomaly differences in China for the selected truncation degrees show that GOCE has improved the accuracy of the global models beyond degree 90 and the accuracies of the models improve from 24 cm to 16 cm. STDs of geoid height differences in USA show that GOSG01S model has best consistency comparing with GPS-leveling data for the frequency band of the degree between 20 and 160.

With the rapid development of gravity gradient measurement, the full tensor gravity gradient data has been used more and more frequently in the edge detection. This article focuses on the problem that the effect of edge detection of deep geological body is not clear and false edges among positive and negative anomalies using the common edge detection method. We present a new edge detection method which is based on the total horizontal derivative and the modulus of full tensor gravity gradient. Comparing with the model experiments, it is proved that this method is clearer and more accurate in detecting the edges of geological body especially for the deep model with almost no false edge interference. Finally, the method is applied to the processing of the actual data in St. Georges Bay, Canada, and the edge results are satisfying.

Full tensor gravity gradient data contain nine signal components. They include higher frequency signals than traditional gravity data, which can extract the small-scale features of the sources. Edge detection has played an important role in the interpretation of potential-field data. There are many methods that have been proposed to detect and enhance the edges of geological bodies based on horizontal and vertical derivatives of potential-field data. In order to make full use of all the measured gradient components, we need to develop a new edge detector to process the full tensor gravity gradient data. We first define the directional Theta and use the horizontal directional Theta to define a new edge detector. This method was tested on synthetic and real full tensor gravity gradient data to validate its feasibility. Compared the results with other balanced detectors, the new detector can effectively delineate the edges and does not produce any additional false edges.

We present a new method dedicated to the interpretation of full gravity gradient tensor data, based on SL0 sparse recovery inversion. The SL0 sparse recovery method aims to find out the minimum value of the objective function to fit the data function and to solve the non-zero solution to the objective function. Based on continuous iteration, we can easily obtain the final global minimum (namely the property and space attribute of the inversion target). We consider which type of tensor data combination produces the best inversion results based on the inversion results of different full gravity gradient tensor data combinations (separate tensor data and combined tensor data). We compare the recovered models obtained by inverting the different combinations of different gravity gradient tensor components to understand how different component combinations contribute to the resolution of the recovered model. Based on the comparison between the SL0 sparse recovery inversion results and the smoothest and focusing inversion results of the full gravity gradient tensor data, we show that SL0 sparse recovery inversion can obtain more stable and efficient inversion results with relatively sharp edge information, and that this method can also produce a stable solution of the inverse problem for complex geological structures. This new method to resolve very large full gravity gradient tensor datasets has the considerable advantage of being highly efficient; the full gravity gradient tensor inversion requires very little time. This new method is very effective in explaining the full gravity tensor which is very sensitive to small changes in local anomaly. The numerical simulation and inversion results of the compositional model indicates that including multiple components for inversion increases the resolution of the recovered density model and improves the structure delineation. We apply our inversion method to invert the gravity gradient tensor survey data from the Vinton salt dome, Louisiana. The results of inversion are in good agreement with the known formation in the region, which supports the validity of our method.

Inflatable structures have numerous advantages, such as small folding size, high deployable reliability, and low cost. This paper accomplishes several tasks with a focus on the gravity-gradient boom of microsatellite. An inflatable boom model balanced by inflatable deployment and delaminating resistance is presented. A system is established to simulate agravic deployment. The inflatable deployment of a tip mass has been tested with the aid of a 3.0 m rolled deployable boom. The perturbation moment during the inflatable deployment is analyzed. Three inflatable booms are tested in a thermal vacuum chamber further. Based on the tests and analyses, the microsatellite which carried an inflatable gravity-gradient boom was launched into orbit successfully in November 2012. After being stored on-orbit for 6 months, the inflatable method was applied to the inflatable boom to unfold the 2.0 kg tip mass steadily at a distance 3.0 m away from the microsatellite in May 2013. This work completes the test of inflatable on-orbit deployment on the base of microsatellite for the first time internationally.

Edge detection is a requisite task in the interpretation of potential field data. There are many methods based on horizontal and vertical derivative of potential field data for edge detection and enhancement. The large eigenvalue of structure tensor can well delineate the edges of geological bodies, but it cannot outline the edges of small amplitude geological bodies clearly. In order to overcome this problem, this paper proposes three different normalization methods to improve the edge detection ability of the large eigenvalue of structure tensor, so that they can display the large and small amplitude edges simultaneously. Also, they do not produce additional false edges when real geological bodies contain positive and negative anomalies simultaneously. These methods were tested on synthetic and measured gravity gradient data and magnetic data. All of the results have shown that the new improved methods are effective for edge detection.

In this paper, the admittance function between seafloor undulations and vertical gravity gradient anomalies was derived. Based on this admittance function, the bathymetry model of 1 minute resolution was predicted from vertical gravity gradient anomalies and ship soundings in the experimental area from the northwest Pacific. The accuracy of the model is evaluated using ship soundings and existing models, including ETOPOl, GEBCO, DTU10 and V15. 1 from SIO. The model's STD is 69.481m, comparable with V15. 1 which is generally believed to have the highest accuracy.

Eigenvalues of the curvature gravity gradient tensor (CGGT) have been utilized to detect and outline edges of geologic bodies. In this paper, we analyzed and discussed the application scope and the limitation of CGGT using a complex synthetic model. We found that the large eigenvalue only can be used to outline edges of positive density bodies, and the small eigenvalue only can be used to delineate edges of negative density bodies. However, in the actual geological situation, the positive and negative density bodies usually coexist simultaneously. Therefore, it has certain limitations to detect edges using this method directly. In view of the limitations of the method, we combined the gravity anomaly with large eigenvalues, and proposed a new improved method for the eigenvalues of CGGT. The improved method can be utilized to outline edges of causative sources in any case. It was tested on synthetic model data and real field data. All of the results have shown that the new improved method is effective for edge detection.

The forces acting upon a rock mass can result in physical changes on either side of the fault plane that are known as fracture zones. This tectonic activity will lead to a difference in the density of fracture zones from the density of surrounding rocks. This condition can be detected using gravity method. The changes of rocks density in contrast to fracture zones are relatively small, so a rigorous technique of gravity data processing to detect its presence is required. This research has developed and implemented the gravity gradient technique as one of the processing and acquisition techniques of gravity data which is found to have a high accuracy to detect the boundaries of rock density contrast changes. For the purposes of analyzing the gravity responses in identifying fracture zones, the characteristics of the gravity and its gradient responses of fracture zones in a strike-slip fault system were analyzed based on the forward and inverse modeling results. Furthermore, the gradient and gravity anomaly inversions were applied to the gravity data towards Palu-Koro strike-slip fault, a segment of the Palu City, Central Sulawesi, Indonesia. The measurement results show that the gravity gradient anomaly has a higher sensitivity compared to its gravity anomaly in detecting the fracture zones. In addition, the inversion result of the gravity gradient anomaly shows that the boundaries of lateral changes in the distribution of density contrast of fracture zones can be identified more accurately.

The average acceleration approach was applied to recover a gravity field model Model_ACA from GOCE precise science orbits from September 2 to November 2, 2010, and furthermore a so called sequential least square adjustment was used. The model was compared with other gravity field models based on CHAMP, GRACE and GOCE. The result shows that the model is superior to gravity field based on CHAMP, and with higher accuracy than other international gravity field models based on only GOCE data before 80 degree. The degree geoid height of Model_ACA reaches 3 cm up to 90 degree and order.

Downward continuation is one of the vital steps in pre-processing of satellite gravity gradient (SGG) data when recovering the earth gravity field by space-wise method. Mathematic downward continuation model of the SGG data based on Poisson integral iteration method was constructed, of which the downward continuation effects based on ‘Direct’ and ‘Remove-Restore’ schemes were analyzed and discussed with simulated SGG data. Results show that the precision of ‘Remove- Restore’ scheme is better than that of the ‘Direct’ scheme at the height of both 5 kilometers and 250 kilometers, i.e., the ‘Remove- Restore’ technique could improve the precision of downward continuation results based on Poisson integral iteration method in a certain degree.

The problem of Earth pointing attitude control for a spacecraft with magnetic actuators is addressed and a complete architecture combining algorithms for detumbling, attitude acquisition and nominal attitude regulation is proposed. Simulation results illustrate the performance of the proposed control law.

We have observed for aerogel nearly filled with superfluid helium that the helium II liquid-vapour interface in the aerogel takes a shape that does not change with respect to gravity (the longest time studied was 3 hr.). the most likely reason we observe a fixed helium II liquid-vapour interface is due to the presence of capillary forces. We have concentrated our studies on the serogel nearly filled with superfluid helium since this is when capillary forces are weakest and least understood. The distribution of helium II in the aerogel is subsequently most susceptible to gravity. We conclude that the helium II liquid-vapour interface will not change shape due to gravitational forces of 1 g for any amount of helium in the aerogel. This makes aerogel a very promising candidate for gravitational missions such as STEP (Satellite Test of the Equivalence Principle) or GOCE (Gravity Field and Ocean Circulation Explorer) that are susceptible to helium II motion. In the case of STEP, gravity gradient forces of magnitude 10−7 g act on the superfluid helium at twice orbital frequency. The motion of helium II produces a gravitational signal in the bandwidth of the STEP measurement. The use of aerogel would eliminate this signal. Thus, trying to isolate this signal by experimental procedure or data analysis is no longer necessary.

The ground-based interferometers currently under construction share their goal and principle of operation with the space project LISA: the detection and measurement of gravitational waves by laser interferometry. There are, however, differences in the frequency ranges (and thus the detectable sources) and in the noise requirements. A lower frequency limit for ground-based detection is, in practice, dictated by seismic noise, and yet more fundamentally by ‘gravity gradient noise’: geophysical, meteorological, and man-made motions of large masses. Ground-based detectors are expected to cover the range from a few Hz to a few kHz. It is only in space that detection of signals below, say, 1 Hz is possible, opening a wide window to a different class of interesting sources of gravitational waves. Actually, many requirements in the ground-based detectors turn out to be more stringent than the ones in space. Thus LISA can profit from a wealth of long-time experience gathered in the prototypes for ground-based interferometers. The recent years have brought a great break-through in the quest for earth-bound detection: on five sites the world over, detectors of armlengths from 0.3 to 4 km are being built. A review of these projects will be given, stressing the similarities, but also the differences, in their respective concepts. First operation of all of the ground-based interferometers is expected around the years 2000/2001, leading to an era of world-wide collaboration in gravitational wave astronomy.

One of the significant application of magnetic fluids technology is given by inertial and gravity sensors. Some of the present and coming achievements in the research, development and applications of various inertial sensors are summarized. The paper presents some results, developed mainly by GRL Bucharest, in particular for applications in acceleration and gravity gradient sensors.

It is shown that microgravity conditions offer the natural environment for the research and applications of magnetic fluid composites. Examples of applications of such media in microgravity conditions are given for inertial and gravitational gradient sensors.

This paper describes the science payloads and experiments of the SUNSAT microsatellite which is to be launched in 1998. A very modular satellite mechanical structure has enabled the addition of additional experiments at a late stage of the program. The design and performance measurements of the engineering and technology payloads (a 10m resolution imager, an accurate ADCS system, a DSP processor board, gravity gradient boom and the solar panels) are reported. The science payloads —including a precision GPS receiver, laser retro-reflectors, magnetometer, and various school experiments — are described, indicating that a very complex microsatellite was developed as the first venture into space by a South African university.

The Lyapunov argument used in Wisniewski and Blanke, (Automatica 35 (1999) 1201) to establish asymptotic stability of a magnetic control law for an earth-orbiting spacecraft is incorrect. It is shown here that a small change to the assumed form of the control law can remedy the situation.

A very large Earth oriented antenna structure which is stabilized by the gravity gradient force is analyzed and its feasibility is discussed. Stresses caused by gravity forces are analytically obtained by assuming that the antenna reflector is a spherical membrane. It is shown that a compression membered flexible reflector maintains its contour by adjusting the length of tethers which connect the reflector and the spacecraft main body.

The ambient level of gravity field is lower over the West African Craton than over the adjacent younger Mauritanides province in West Africa. The stacks of Bouguer gravity profiles taken across the region over which the ambient gravity field is distinctly different on either side are broadly outlined by minima and maxima anomalies with well-defined steep gravity gradient separating them. The crustal structure on either side of this steep gradient is clearly different. To the east the negative anomalies are over the craton and to the west the positive anomalies are over the younger Mauritanides structure. The gravity maxima with an amplitude of about 50 mgal is considered as the gravity signature of the boundary between the two structural units. The western outline of the craton in Mauritania and Senegal has been delineated on the basis of this gravity signature. The interpretation suggests that there has been overthrusting of the Mauritanides onto the craton of between 50 to 120 km. In Senegal, this interpretation is in close agreement with seismic result which indicates thrusting of about 80 km of the Mauritanides onto the craton. The western limit of the craton in the study area is concealed beneath Mauritanides fold belt making gravity survey more appropriate tool for its delineation than surface mapping as it can delineate structural boundary over hidden basement or where structural units have been overthrust.

It is shown to be possible to damp small oscillations of a gravity gradient stabilized satellite in circular orbit by three changes of the mass distribution. The time program of the changes is calculated for the linearized equations of motion. Using the program for the nonlinear motion some parameters must be varied.