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The three spacecraft which constitute the Swarm mission are equipped with the Micro Advanced Stellar Compass (μASC) provided by the Technical University of Denmark (DTU) for attitude determination. Each μASC is comprised of three Camera Head Units (CHUs) for a total of nine cameras on the mission. The CCD sensor inside the CHUs are sensitive to energetic particle irradiation which appear as transient bright pixels dubbed ’Energetic Particle Detections’ (EPDs) on the star field images. For more than five years the μASCs on-board Swarm have transmitted the occurrence of EPDs to ground and thereby effectively added high energy radiation monitoring capabilities to the Swarm mission. The high sensitivity, high sample rate (1-2 Hz), orientation of the camera heads, simultaneous measurements from all three spacecraft and near-polar orbits at an altitude of 450-510 km and allows for continuous and real-time monitoring of the high energy (>65 MeV) proton environment in LEO. This data uncover short and long term changes in particle flux in e.g. the South Atlantic Anomaly (SAA) of relevance for future mission planning. The same radiation monitoring capability exists on NASA’s Magnetospheric Multiscale Mission (MMS) which, due to its highly elliptical orbit, survey the Van Allen radiation belts and detect enhanced radiation levels in the belts associated with geomagnetic storms. Combining data from the μASCs onboard Swarm and MMS provides unique insight into the injection mechanisms and dynamics of very high energy particles which is currently poorly understood. This work presents observations and results using high energy radiation data obtained from the μASC on board ESA’s Swarm mission, from February 2018 to February 2023, in combination with μASC data from MMS.

© 2022 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. In this article, we show the capability of a global navigation satellite system (GNSS) precise orbit determination (POD) low Earth orbit (LEO) data to detect anomalous ionospheric disturbances in the spectral range of the signals associated with earthquakes and tsunamis, applied to two of these events in Papua New Guinea (PNG) and the Solomon Islands during 2016. This is achieved thanks to the new PIES approach (POD-GNSS LEO Detrended Ionospheric Electron Content Significant Deviations). The significance of such ionospheric signals above the swarm LEOs is confirmed with different types of independent data: in situ electron density measurements provided by the Langmuir Probe (LP) onboard swarm LEOs, DORIS, and ground-based GNSS colocated measurements, as it is described in this article. In this way, we conclude the possible detection of the tsunami-related ionospheric gravity wave in PNG 2016 event, consistent with the most-recent theory, which shows that a tsunami (which is localized in space and time) excites a spectrum of gravity waves, some of which have faster horizontal phase speeds than the tsunami. We believe that this work shows as well the feasibility of a future potential monitoring system of ionospheric disturbances, to be made possible by hundreds of CubeSats with POD GNSS receivers among other appropriate sensors, and supported for real-time or near real-time confirmation and characterization by thousands of worldwide existing ground GNSS receivers. This work has been partially supported by the COSTO ESA-funded project (ESA ITT AO/1-9514/18/NL/IA). Also it was partially supported by the 2017 SGR-0851 grant of the Generalitat de Catalunya and by the EU project 101007599 - PITHIA-NRF. The data for this paper are available and they can be requested from H. Yang (h.yang@upc.edu) and M. Hernandez-Pajares (manuel.hernandez@upc.edu).

ELF/VLF waves have been registered in the outer polar cusps simultaneously with high energy electrons fluxes by the satellites Magion 4 (subsatellite to Interball 1), Polar and CLUSTER. Further, we discuss similar observations in the different regions of the ionosphere, where DEMETER registered energetic electrons. The DEMETER satellite operating on the nearly polar orbit at the altitude 650 km crossed different regions in the ionosphere. Registrations of ELF/VLF/HF waves together with the energetic electrons in the polar cusp, in the ionospheric trough and over thunderstorm areas are presented in this paper. The three satellites of ESA’s Swarm mission provide additional information on the ELF waves in the mentioned areas together with electron density and temperature. A brief discussion of the generation of these emissions by the so-called “fan instability” (FI) and beam instability is presented.

The lithospheric magnetic field, which is one of the main objectives of ESA’s mission Swarm, is slowly varying in time due to an induced component. This variation is small (usually it is omitted in the lithospheric modelling) but recent advances in processing strategies and still-growing amount of satellite data open questions whether such an effect should be considered in the development of the lithospheric models—when using data from missions like CHAMP and Swarm. This effect can now be estimated over a period of 17 years (since the launch of CHAMP), and it is shown how the satellite measurements (over the observable part of the spectrum) can be referenced to one common epoch. For this purpose, we first inverted the magnetic field vector from CHAOS-6 over degrees 21–120, after subtraction of a remanent model, to a vertically integrated susceptibility map. Using this susceptibility distribution and taking into account the evolving core fields from the CHAOS-6 model, the time-varying lithospheric signal is computed. The results depend on the time span and the altitude considered, e.g., an altitude of 400 km and a span of 17 years can produce more than 0.5 nT variations resulting in a peak-to-peak value of nearly 1 nT. The vertically integrated quantities appear to be a useful choice for parameterising lithospheric time variations, also for providing data corrections at the satellite altitude. The effect of the choice of the core field, which enters the inversion, on the lithospheric time variation is also studied—this effect is found less important even for core fields 20 years apart.

The study investigates Swarm data including in-situ electron density (ED) measured by Langmuir Probes (LP) and total electron content (TEC) from precise orbit determination (POD) GNSS receivers in time of Chile-Illapel earthquake (EQ) and tsunami in 2015. The research is based on the symbiosis of Swarm data, ground GNSS data and seismic records combined with the information on EQs and tsunamis. The FFT-based filtering and short-term Fourier transform (STFT) analysis are used in detection of seismic ionospheric disturbances (SID) in ED from LP and POD TEC data. The classification of the spectral characteristics of disturbing along-track signals is supported by their simultaneous search in ground GNSS observations, which gives an opportunity for the validation of the spectral recognition. Ground GNSS data, due to several tens of satellites and thousands of stations, provide the only full spatiotemporal view on SIDs and enable the inspection of their spatial shapes, spatial relations and speeds. The location of dense ground GNSS networks is however limited to selected places. Swarm and other LEO satellite data, in turn, are globally distributed, but they are dense only along the orbital tracks. Therefore, 1D nature of Swarm along-track observations, fast satellite movement and limited chance for spatiotemporal correlation due to the non-repeating orbits, strongly require spectral analysis for better recognition of the signals. The detection of SIDs from along-track Swarm data is also complicated due to the variety of disturbing signals occurring in the ionosphere, and the spectral analysis is also crucial there. STFT spectral approach to along-track Swarm data gives an opportunity for distinguishing the signals of different origin. The analyses of Swarm data provide interesting observations of ionospheric disturbances not only directly related with the largest EQ events and tsunami, but also occurring during entire periods of enhanced seismic activity and at larger distances from EQ epicenter. The disturbing signals triggered by the largest EQs and tsunami were also observed. However their amplitude in the ionosphere is not always such dominating as the amplitude of some other, associated disturbances on the neighboring days. This difference in scale can suggest that the electron disturbances in the ionosphere are rather more generally related to the crustal motion and seismic activity, than solely correlated with large EQs.

Applying a multi-parametric approach, we already investigated the preparatory phase of several medium and large (M6.0 ~ M8.3) earthquakes occurred in the last 6 years in different locations in the World. In some cases, a chain of processes from the lithosphere to atmosphere and ionosphere has been successfully detected (e.g. M7.8 Ecuador 2016: Akhoondzadeh, 2018, ASR, https://doi.org/10.1016/j.asr.2017.07.014; Italian seismic sequence (M6.5) 2016-2017: Marchetti et al., 2019, RSoE, https://doi.org/10.1016/j.rse.2019.04.033; M7.5 Indonesia 2018: Marchetti et al., 2019, JAES, https://doi.org/10.1016/j.jseaes.2019.104097). These analyses underline the importance to study all the “spheres” that surround the Earth as suggested by a Geosystemic approach (De Santis et al., 2019, Entropy, https://doi.org/10.3390/e21040412). To analyse the anomalies that occur in the atmosphere we typically calculate the mean and standard deviation of the “historical time series” of the investigated parameter based on around 40 years of data, and then we superpose the value of the same quantity in the earthquake year. If the value overpasses two standard deviations of the historical time series, we define this day/parameter as anomalous. Applying the same methodology presented in previous works that studied climatological parameters such as skin temperature, total column water vapour, aerosols, and SO2, which seem to provide anomalies possibly related to the earthquake preparation phase (e.g. Piscini et al., 2017, PAGeoph, https://doi.org/10.1007/s00024-017-1597-8), here we investigate more atmospheric parameters proposed as possible precursors in the Lithosphere Atmosphere Ionosphere Coupling (LAIC) models (Pulinets and Ouzounov, 2011, JAES, https://doi.org/10.1016/j.jseaes.2010.03.005) such as methane and surface concentration of carbon monoxide. Other parameters, such as dimethylsulfide could be useful in other geophysical events, such as the volcano eruptions (Piscini et al. PAGeoph 2019, https://doi.org/10.1007/s00024-019-02147-x).In this study, we also apply a Worldwide Statistical Correlation (WSC), as it was successfully applied to Swarm satellites electromagnetic anomalies and earthquakes, providing some statistical evidence for such perturbations in ionosphere before the occurrence of M5.5+ earthquakes (De Santis et al., 2019, Sci. Rep., https://doi.org/10.1038/s41598-019-56599-1).The statistical approaches applied to these climatological data, provided by meteorological agencies such as ECMWF and NOAA, provides some interesting concentrations of atmospheric anomalies, preceding from days to several weeks the occurrence of the largest earthquakes from 1980 to 2017.The study of several chemical and physical (e.g. aerosol particles) components in the atmosphere, the involved physical processes, the chemical reactions and chemical constraints (such as the elements lifetime and interactions in the atmosphere) can help to distinguish which LAIC model is more reliable to produce the observed anomalies before the occurrence of a large earthquake.

In the past decade, it has been shown that atomic quantum sensors are a newly emerging technology that can be used for measuring the Earth’s gravity field. Whereas classical accelerometers, based e.g. on capacitive sensing and electrostatic actuation, are limited by relatively high noise at low frequencies, Cold Atom Interferometers (CAI) can be highly accurate over the entire frequency range, which also has the benefit that they do not need any calibration phase. Several studies related to these new sensor concepts were initiated at ESA, mainly focusing on technology development for different instrument configurations (gravity gradiometers and satellite-to-satellite ranging systems) and including validation activities, e.g. two successful airborne surveys with a CAI gravimeter. We will present the first conclusions of these different mission and instrument studies:The first airborne gravity survey during the ESA Cryovex/KAREN 2017 campaign using this technology was conducted by DTU and ONERA. The measurements did not show any drift and the accuracy was found to be less than 4 mGal at 11 km resolution. A second campaign has been conducted by ONERA and CNES in 2019 in the South of France and improved the accuracy by a factor 4, reaching classical airborne survey state-of the art performance. A first space quantum gravity mission concept is based on a gravity gradiometer that delivers a very high common mode rejection, greatly relaxing the drag-compensation requirements. The second concept is based on quantum accelerometers for correcting low frequency errors of electrostatic accelerometers that are used in a low-low satellite-to-satellite ranging concept in order to measure non-gravitational accelerations. For both concepts we will present the expected improvement in measurement accuracy and in the derived Earth gravity field models, taking into account the different types of measurement (e.g. single axis vs. three axis, integration time, etc.) and different mission parameters (e.g. attitude control, altitude of the satellite, lifetime of the mission, etc.). A technology roadmap will be outlined for potential implementation of a quantum inertial sensor geodesy mission within 10-15 years.

The Earth masses reside in a near-hydrostatic equilibrium, while the deviations are, for example, manifested in the geoid, which is nowadays well determined by satellite gravimetry. Recent progress in estimating the density distribution of the Earth allows us to examine individual Earth layers and to directly see how the sum approaches the observed anomalous gravitational field. This study evaluates contributions from the crust and the upper mantle taken from the LITHO1.0 model and quantifies the gravitational spectra of the density structure to the depth of 435 km. This is done without isostatic adjustments to see what can be revealed with models like LITHO1.0 alone. At the resolution of 290 km (spherical harmonic degree 70), the crustal contribution starts to dominate over the upper mantle and at about 150 km (degree 130) the upper mantle contribution is nearly negligible. At the spatial resolution $$

Space weather phenomena such as scintillations of Global Navigation Satellite Systems (GNSS) signals are of increasing importance for aviation, the maritime, and civil engineering industries. The ionospheric plasma irregularities causing scintillations are associated with strong gradients in ionospheric plasma density. To provide nowcasts and forecasts of space weather effects, it is vital to monitor the ionosphere and detect strong density variations. To reconstruct plasma density variations in the polar cap ionosphere, we use total electron content (TEC) estimates from the Swarm satellites' GPS receivers. By considering events where the Swarm satellites are in close proximity, we obtain plasma density variations by inverting TEC measurements on a two-dimensional grid. We first demonstrate the method using synthetic test data, before applying it to real data. The method is validated using in situ Langmuir probe measurements and ground-based TEC observations. We find that the new method can reproduce density variations, although it is sensitive to the geometry of the Swarm satellite constellation and to the calculated plasma temperature. Our proposed method opens new possibilities for ionospheric plasma monitoring that uses GPS receivers aboard low Earth orbit (LEO) satellites.

International audience; Lightnings and particularly TLEs (sprites, jets, elves, halos) are associated with the electromagnetic connections and interactions between atmosphere, ionosphere and magnetosphere. DEMETER was a low-altitude microsatel-lite, it operated from June 2004 till December 2010 on a polar, circular orbit which altitude at the beginning was 710km but it was decreased to 660 km. DEMETER measured variations of the electric field in low frequency range from 0 to 20 kHz. The plasma analyzer instrument measured variations of the ion density 4 s time resolution. Langmuir probe gave the value of the electron temperature and density. A detector of energetic particle measured electrons and protons with energies from 70 keV to 2.34MeV every 4 s in survey mode and 1 s in burst mode. DEMETER has clearly shown, that thunderstorms and TLE can affected the ionosphere even at altitude of its orbit (680km). It registered many strong thunderstorms in Poland during its time of operation. The Swarm constellation comprises 3 identical satellites launched on 22 November 2013 into a near-polar orbit. This set of satellites is still operating. Two of them are operating on the circular, polar orbits with initial altitude 460. Third one has also circular orbit, but with altitude 530. The orbits of the first 2 satellites are in almost the same plane, but third one is close to be perpendicular to the first two. The payload containing Vector Field Magnetometer, Absolute Scalar Magnetometer and Electric Field Instrument among other allows to study the effects in the ionosphere generated by thunderstorms. The measurements performed during flights over thunderstorms areas in Poland will be discussed in our presentation. The discussion of the cross correlation between the ground based registrations (PERUN and VERA systems) and DEMETER and Swarm measurements of the ULF/ELF/VLF waves, electron density and temperature variations in the ionosphere related to the strong thunderstorms in Poland will be presented.

In this chapter the application of the curlometer technique to various regions of the inner magnetosphere and upper ionosphere and for special circumstances of sampling is described. The basic technique is first outlined, together with the caveats of use, covering: the four-spacecraft technique, its quality factor and limitations; the lessons learnt from Cluster data, together with issues of implementation, scale size and stationarity, and description of the key regions covered by related methodology. Secondly, the application to the Earth’s ring current region is outlined, covering: the application of Cluster crossings to survey the ring current; the use of the MRA (magnetic rotation analysis) method for field curvature analysis; the use of THEMIS (Time History of Events and Macroscale Interactions during Sub-storms mission) three-spacecraft configurations to sample the ring current, and future use of MMS (Magnetospheric MultiScale mission) and Swarm data, i.e. the case of small separations. Thirdly, the application of the technique to the low altitude regions covered by Swarm is outlined, covering: the extension of the method to stationary signals; the use of special configurations and adjacent times to achieve 2, 3, 4, 5 point analysis; the use of the extended ‘curlometer’ with Swarm close configurations to compute 3-D current density, and a brief indication of the computation of current sheet orientation implied by 2-spacecraft correlations. Fourthly, the direct coordination of Cluster and Swarm to check the scaling and coherence of field-aligned currents (FACs) is outlined.

We propose a concept for future space gravity missions using cold atom interferometers for measuring the diagonal elements of the gravity gradient tensor and the spacecraft angular velocity. The aim is to achieve better performance than previous space gravity missions due to a very low white noise spectral behavior and a very high common mode rejection, with the ultimate goals of determining the fine structures of the gravity field with higher accuracy than GOCE and detecting time-variable signals in the gravity field better than GRACE., Comment: 10 pages, 6 figures The final publication is available at Springer via http://dx.doi.org/10.1007/s12217-014-9385-x. appears in Microgravity Science and Technology October 2014

We combine the advantages of multi-spacecraft and ground-based monitoring of the geospace environment in order to analyze and study magnetospheric ultra low frequency (ULF) waves. In line with this aim, we also develop and deliver relevant analysis tools based on wavelet transforms and tailored to the Swarm mission. In the preparation phase as well as the lifetime of the Swarm mission, the analysis of isolated ULF wave events— especially those detected in the Pc3 frequency range (20–100 mHz) that a topside ionosphere mission efficiently resolves—can help to elucidate the processes that play a crucial role in the generation of waves and their most defining propagation characteristics. Additionally, we offer a useful platform to monitor the wave evolution from the outer boundaries of Earth’s magnetosphere through the topside ionosphere down to the surface. Data from a single Low Earth Orbit (LEO) satellite (CHAMP), a multi-satellite LEO mission (ST5) and the ongoing multi-satellite magnetospheric mission (Cluster) along with a ground-based magnetic network (CARISMA) are used to demonstrate the potential of our analysis technique in studying wave evolution in detail. A better understanding of the generation and propagation of waves will also allow to geophysically validate some of Swarm’s data products, especially those related to the magnetic and electric fields in geospace. With a carefully selected case study focusing on the recovery phase of a moderate magnetic storm (9 April 2006 with a minimum Dst value of −82 nT) as a starting point, we clearly demonstrate the capabilities offered by our wavelet analysis tools and highlight the options opened to treat various categories of multipoint multi-instrument measurements (both spaceborne and ground-based) for signatures of ULF wave signals as well as the effects of various other sources.

Machine learning techniques have been successfully introduced in the fields of Space Physics and Space Weather, yielding highly promising results in modeling and predicting many disparate aspects of the geospace environment. Magnetospheric ultra-low frequency (ULF) waves can have a strong impact on the dynamics of charged particles in the radiation belts, which can affect satellite operation. Here, we employ a method based on Fuzzy Artificial Neural Networks in order to detect ULF waves in the time series of the magnetic field measurements on board the low-Earth orbit CHAMP satellite. The outputs of the method are validated against a previously established, wavelet-based, spectral analysis tool, that was designed to perform the same task, and show encouragingly high scores in the detection and correct classification of these signals.

The Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite aimed at determining the Earth’s mean gravity field. GOCE delivered gravity gradients containing directional information, which are complicated to use because of their error characteristics and because they are given in a rotating instrument frame indirectly related to the Earth. We compute gravity gradients in grids at 225 km and 255 km altitude above the reference ellipsoid corresponding to the GOCE nominal and lower orbit phases respectively, and find that the grids may contain additional high-frequency content compared with GOCE-based global models. We discuss the gradient sensitivity for crustal depth slices using a 3D lithospheric model of the North-East Atlantic region, which shows that the depth sensitivity differs from gradient to gradient. In addition, the relative signal power for the individual gradient component changes comparing the 225 km and 255 km grids, implying that using all components at different heights reduces parameter uncertainties in geophysical modelling. Furthermore, since gravity gradients contain complementary information to gravity, we foresee the use of the grids in a wide range of applications from lithospheric modelling to studies on dynamic topography, and glacial isostatic adjustment, to bedrock geometry determination under ice sheets.

We show for the first time, with direct, multispacecraft calculations of electric current density, and other methods, matched signatures of field-aligned currents (FACs) sampled simultaneously near the ionosphere at low (similar to 500km altitude) orbit and in the magnetosphere at medium (similar to 2.5 R-E altitude) orbits using a particular Swarm and Cluster conjunction. The Cluster signatures are interpreted and ordered through joint mapping of the ground/magnetospheric footprints and estimation of the auroral zone boundaries (taken as indication of the boundaries of Region 1 and Region 2 currents). We find clear evidence of both small-scale and large-scale FACs and clear matching of the behavior and structure of the large-scale currents at both Cluster and Swarm. The methodology is made possible through the joint operations of Cluster and Swarm, which contain, in the first several months of Swarm operations, a number of close three-spacecraft configurations.

International audience; Data from the first year of ESA's Swarm constellation mission are used to derive the Swarm Initial Field Model (SIFM), a new model of the Earth's magnetic field and its time variation. In addition to the conventional magnetic field observations provided by each of the three Swarm satellites, explicit advantage is taken of the constellation aspect by including east-west magnetic intensity gradient information from the lower satellite pair. Along-track differences in magnetic intensity provide further information concerning the north-south gradient. The SIFM static field shows excellent agreement (up to at least degree 60) with recent field models derived from CHAMP data, providing an initial validation of the quality of the Swarm magnetic measurements. Use of gradient data improves the determination of both the static field and its secular variation, with the mean misfit for east-west intensity differences between the lower satellite pair being only 0.12 nT.

Gravity observations made over the Groningen gasfield from 1978 onwards are available. The existing gravity data were reanalysed and a new survey was carried out. The observed gravity changes obtained during four surveys, spanning an 18-year period, were compared with the gravity effect due to natural gas extraction computed from the reservoir model and the production data. The random error in the gravity values is small enough to detect the effect of gas extraction after a few years (up to 2 μgal/year). The trends obtained from observed and calculated gravity changes agree well within their expected error margins after statistical data snooping. Due to the inadequate measurement set-up of the previous surveys, systematic errors present in the gravity data hampered the use of this data for refinement of the reservoir and the production models. However, with improved gravity monitoring, in particular a very systematic network set-up and well-calibrated instruments, this should now be feasible. By using the network analysis from the 1996 measurements for the planning of a network in space and time, most of the current problems can be avoided.

We discuss the gravity gradient signal measured at the height of the GOCE satellite and compare it with the gravity gradients related to the density contrast between crust and mantle. The gravity gradients are reduced for the topographic masses to emphasize the lithospheric signal. Comparison with the Moho-related signal shows that with a density contrast of 400 kg/m3, the amplitude of the calculated gradients is almost twice that of the observed field. The differences can only partly be explained by the uncertainty of the crustal thickness, but is clearly related to the applied density contrast. Calculation of the gravity gradients requires a reduced density contrast, which is an important consideration for establishing global models, which might otherwise overestimate crustal thickness.

Abstract A 3D basin modeling study was carried out to reconstruct the regional heat flow and source rock maturity in the Rub'al-Khali basin. Gravity gradient data from the GOCE satellite were used to model deep structures, such as the Moho interface. Tectonic heat flow was modeled using the GOCE-based Moho interface to reflect heat flow variations in the basin though time and space. The thermal maturity of Silurian and Jurassic source rocks in the Rub'al-Khali was calculated using the GOCE-constrained basal heat flow model. GOCE-based Moho depth map was calibrated to data from known seismic stations in the region. This map provided input to constrain the heat flow in eth basin. Modeled heat flow values are consistent with known values of heat flow in the region. The model indicates that the Silurian and Jurassic source rocks are generally in the hydrocarbon generation window and the modeled maturity trends are in agreement with the observations in the area.

A 3D basin modeling study was carried out to reconstruct the regional heat flow and source rock maturity in the Rub'al-Khali basin. Gravity gradient data from the GOCE satellite were used to model deep structures, such as the Moho interface. Tectonic heat flow was modeled using the GOCE-based Moho interface to reflect heat flow variations in the basin though time and space. The thermal maturity of Silurian and Jurassic source rocks in the Rub'al-Khali was calculated using the GOCE-constrained basal heat flow model. GOCE-based Moho depth map was calibrated to data from known seismic stations in the region. This map provided input to constrain the heat flow in eth basin. Modeled heat flow values are consistent with known values of heat flow in the region. The model indicates that the Silurian and Jurassic source rocks are generally in the hydrocarbon generation window and the modeled maturity trends are in agreement with the observations in the area. Copyright 2014, International Petroleum Technology Conference. ConocoPhillips; et al.; ExxonMobil; Maersk Oil; Qatar Petroleum; Shell

In this paper the main results concerning the preparatory studies of a future ESA Earth Observation gravity mission are presented: the mission will be ultimately devoted to improve our understanding of the Earth’s mass transport phenomena, the temporal variations of the gravity field, at different temporal and spatial scales, being caused by mass changes of ice sheets and ice caps, continental water cycles, ocean masses dynamics and solid-earth deformations. The “Assessment of a Next Generation Gravity Mission for Monitoring the Variations of the Earth’s Gravity” study (concisely: NGGM) consisted of two parallel activities followed by two consortia: each one has involved European universities and academic institutions for scientific support and requirement assessments, in addition to experts in mission analysis and measurement technologies. Several mission concepts have been studied with well-defined science requirements and accurate sub-system designs: in addition to the drivers due to tight propulsion requirements and accelerometer calibration issues, the technical constraints on power and fuel may dictate the choice of orbit. Thus, for each considered constellation type, the different interactions between dragfree and “loose” formation control have been analyzed, together with the design of the relative attitude control, necessary to ensure the laser link for inter-satellite distance measurement all along the mission phases. The latest results concerning the proposed satellite architectures, laser metrology, attitude and orbit control system and formation flying control concepts are presented in the paper, together with the on-going activities for increasing the technological readiness level of the main subsystems. A broad overview is given on the status of the miniaturized RIT and mN-FEEP breadboarding and testing for what concerns the micro-propulsion subsystem, while, concerning the laser metrology, the laser head and the laser stabilization device are described at unit level, with a discussion on the thermal requirements derivation.

In recent years, global gravity models, both based only on satellite data and from combination with terrestrial data, are increasingly available and particularly useful to construct regional models before more local interpretations on the exploration scale are carried out. Often it is challenging to distinguish clearly between near-surface and regional or even subcrustal signals in the gravity field. Applying simple techniques like wavelength-filtering might lead to an incorrect estimate of the regional and residual field, which may significantly alter estimates of the thickness of sedimentary basins or the size of mineral deposits. An alternative is to use satellite gravity gradients to establish the regional components before studying local geology. Sampietro (2011) presented a global Mohorovicic discontinuity (Moho) depth map, which sparked a discussion about the validity of such results. Especially the question remains about whether crustal thickness estimates based on Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite data have a higher accuracy than models based on global gravity models or terrestrial data. For example, the density contrast between crust and mantle remains a main factor of uncertainty. Here we join this discussion by describing how satellite gravity gradients can be used in addition to terrestrial data sets or global models like EGM2008, and how the combined use of data sets at multiple levels above the Earth’s surface can help confine the uncertainty in both regional and local modeling studies

We present a case study for the North-East Atlantic margin, where we analyze the use of satellite gravity gradients by comparison with a well-constrained 3D model. The model is based on a wealth of seismic profiles, commercial and scientific borehole data from the shelf and mainland Norway, petrophysical sampling and a dense coverage of gravity and aeromagnetic data. The 3D model provides a detailed picture from the upper mantle to the top basement (base of sediments). We analyze how gravity gradients can increase confidence in the modeled structures. Initial results indicate for example that a lateral variable surface density, which reflects geology, has a small influence on the gravity gradients at satellite height. However, the gravity gradients are sensitive to the crustal geometry and upper mantle density structure, which make them an ideal addition to forward and inverse modeling of the lithosphere. The next step will be to calculate a sensitivity matrix for the entire 3D model. This sensitivity matrix describes the relation between calculated gravity gradient data and geological structures with respect to their depth, extent and relative density contrast, and will be used for joint inversion of gravity and gravity gradients.

Launched on March 17th 2009 from the Plesetsk Cosmodrome (Northern Russia), GOCE maps the Earth’s gravity field with unprecedented accuracy and resolution and will be of benefit for many branches of Earth science. This paper gives an overview of the European Space Agency’s (ESA) recent technical developments and activities going beyond the GOCE mission and its technology. It describes the outcome of the recent Laser SST concept studies, the Laser metrology concept and the objectives of the ongoing parallel Next Generation Gravimetry Mission studies, together with an overview on the latest technology development studies on atomic clocks and atom interferometry for possible future gravity sensing.

In 2009 the European Space Agency satellite mission GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) was launched. Its objectives are the precise and detailed determination of the Earth’s gravity field and geoid. Its core instrument, a three axis gravitational gradiometer, measures the gravity gradient components V xx , V yy , V zz and V xz (second-order derivatives of the gravity potential V) with high precision and V xy , V yz with low precision, all in the instrument reference frame. The long wavelength gravity field is recovered from the orbit, measured by GPS (Global Positioning System). Characteristic elements of the mission are precise star tracking, a Sun-synchronous and very low (260 km) orbit, angular control by magnetic torquing and an extremely stiff and thermally stable instrument environment. GOCE is complementary to GRACE (Gravity Recovery and Climate Experiment), another satellite gravity mission, launched in 2002. While GRACE is designed to measure temporal gravity variations, albeit with limited spatial resolution, GOCE is aiming at maximum spatial resolution, at the expense of accuracy at large spatial scales. Thus, GOCE will not provide temporal variations but is tailored to the recovery of the fine scales of the stationary field. GRACE is very successful in delivering time series of large-scale mass changes of the Antarctic ice sheet, among other things. Currently, emphasis of respective GRACE analyses is on regional refinement and on changes of temporal trends. One of the challenges is the separation of ice mass changes from glacial isostatic adjustment. Already from a few months of GOCE data, detailed gravity gradients can be recovered. They are presented here for the area of Antarctica. As one application, GOCE gravity gradients are an important addition to the sparse gravity data of Antarctica. They will help studies of the crustal and lithospheric field. A second area of application is ocean circulation. The geoid surface from the gravity field model GOCO01S allows us now to generate rather detailed maps of the mean dynamic ocean topography and of geostrophic flow velocities in the region of the Antarctic Circumpolar Current.

The European Space Agency (ESA) released a Call for Proposals for the next Earth Explorer Core Mission in March 2005, with the aim to select the 7th Earth Explorer (EE-7) mission for launch in the next decade [1]. Twenty-four proposals were received and subject to scientific and technical assessment. Six candidate missions were selected and further investigated in the preliminary feasibility studies (Phase 0). A further down-selection was made after the User Consultation Meeting held in Lisbon, Portugal in January 2009. Three candidate missions were selected for further feasibility investigations (phase A). Each of the candidate missions is now being defined in detail through two parallel and competing industrial studies and many complementary science and technology studies, aiming to the final down-selection in 2011/12, followed by the mission implementation with a planned launch in the 2016/17 timeframe.

A method for the computation of second derivatives Tuu, Tvv, and Tzz of the disturbance gravity potential from altimetric geoid profiles is proposed. Both the high precision and the data density in profile direction are optimally used when determining the second derivatives Tuu from ascending and Tvv from descending tracks. The differentiation is performed with smoothing cubic B‐splines. At the intersection points of the profiles ∂(δg)/∂z = −Tzz is determined by Laplace's equation. No gridding of data is needed. The method has been tested with Seasat data in the North Atlantic. The signal rms is of Tuu, Tvv is 7.4#lb10−9 s−2 that of Tzz 10.2#lb10−9 s−2.

It is shown by means of an extensive simulation study as well as an experiment using real CHAMP data that it is feasible to accurately estimate non-conservative accelerations from precise GPS-based orbit perturbations. Assuming the availability of high-precision gravity field models, such as anticipated for GRACE and GOCE, an accuracy of better than 50 nm/s2 seems possible for 30-seconds averaged accelerations. The remaining dominant error sources seem to be GPS receiver carrier-phase noise and GPS ephemeris errors.

This paper introduces the first ESA Core Earth Explorer mission, GOCE. in the context of ESA’s Living Planet programme. GOCE will measure highly accurate, high spatial resolution differential accelerations in three dimensions along a well characterised orbit: the mission is planned for launch in early 2006. The mission objectives are to obtain gravity gradient data such that new global and regional models of the static Earth’s gravity field and of the geoid can be deduced at length scales down to 100 km. These products will have broad application in the fields of geodesy, oceanography, solid-earth physics and glaciology.

The fast development of new IT-tools and communication technologies provides new opportunities for computer mediated collaboration in geographically distributed groups. One of the fields suitable for application of these technologies is collaboration among scientists. This opportunity is especially important to many of the smaller European countries where it may be difficult to maintain competent scientific research within highly specialized fields. The new tele-communication technologies provide scientists in smaller countries with opportunities to maintain close collaboration with colleagues in foreign countries in spite of dispersion in time and geographical location, and combined with multimedia to enhance visual representations of scientific data they open up radically new dimensions in research.