DETERMINISTICALLY-MODIFIED INTEGRAL ESTIMATORS OF GRAVITATIONAL TENSOR

The Earth’s global gravity field modelling is an important subject in Physical Geodesy. For this purpose different satellite gravimetry missions have been designed and launched. Satellite gravity gradiometry (SGG) is a technique to measure the second-order derivatives of the gravity field. The gravity field and steady state ocean circulation explorer (GOCE) is the first satellite mission which uses this technique and is dedicated to recover Earth’s gravity models (EGMs) up to medium wavelengths. The existing terrestrial gravimetric data and EGM scan be used for validation of the GOCE data prior to their use. In this research, the tensor of gravitation in the local north-oriented frame is generated using deterministically-modified integral estimators involving terrestrial data and EGMs. The paper presents that the SGG data is assessable with an accuracy of 1-2 mE in Fennoscandia using a modified integral estimatorby the Molodensky method. A degree of modification of 100 and an integration cap size of 2.5° for integrating 5´x5´ terrestrial data are proper parameters for the estimator

Benefit of Quantum technology for future earth observation from space - gradiometry case

A big interest exists in geoscience disciplines to know the mass variations of the Earth with high resolution and accuracy. For monitoring climate change processes at the required level, it is essential to select the appropriate sensor technology and satellite missions. Future satellite missions will strongly depend on the advancement of novel technology and dedicated observation concepts of the Earth's gravitational field. The first objective of this study is to characterize various quantum and hybrid gradiometer concepts and to describe their respective error properties. As a result of their white noise behavior at low frequencies, Cold Atom Interferometry (CAI) accelerometers and gradiometers are perfectly suited as complementary methods to classical electrostatic concepts. Future gravity satellite missions could greatly benefit from accelerometers and gradiometers applying atom interferometry, alone or in some hybrid constellation. The comparison will demonstrate the differences in the spectral behavior as well as the mutual benefit of CAI-based and classical electrostatic gradiometers (as used in GOCE). Using simulated atom-interferometric and hybrid gradient measurements along one or more gradiometer axes in GOCE-like orbits, we determine the gravity field in spherical harmonics coefficients for the various cases and discuss the pros and cons of the selected concepts

DETERMINISTICALLY-MODIFIED INTEGRAL ESTIMATORS OF GRAVITATIONAL TENSOR

The Earth's global gravity field modelling is an important subject in Physical Geodesy. For this purpose different satellite gravimetry missions have been designed and launched. Satellite gravity gradiometry (SGG) is a technique to measure the second-order derivatives of the gravity field. The gravity field and steady state ocean circulation explorer (GOCE) is the first satellite mission which uses this technique and is dedicated to recover Earth's gravity models (EGMs) up to medium wavelengths. The existing terrestrial gravimetric data and EGM scan be used for validation of the GOCE data prior to their use. In this research, the tensor of gravitation in the local north-oriented frame is generated using deterministically-modified integral estimators involving terrestrial data and EGMs. The paper presents that the SGG data is assessable with an accuracy of 1-2 mE in Fennoscandia using a modified integral estimatorby the Molodensky method. A degree of modification of 100 and an integration cap size of for integrating terrestrial data are proper parameters for the estimator

Quantum technology for future earth observation from space - gradiometry case

In various geoscience disciplines, there is a huge interest in knowing the mass variations of the Earth with high resolution and accuracy. It is vital for monitoring climate change processes to define corresponding requirements for the sensor technology and for possible satellite missions. The future satellite missions will strongly depend on the advancement of novel technology and beneficial observation concepts of the Earth gravitational field. In this study, various quantum and hybrid gradiometer concepts are first characterized and corresponding error properties are described. Here, special attention is paid to Cold Atom Interferometry (CAI) accelerometers and gradiometers that will perfectly supplement the classical electrostatic concepts due to their white noise behavior at low frequencies. Those, accelerometers and gradiometers using atom interferometry have great potential for increasing the accuracy of future gravity satellite missions. We will compare hybrid with classical electrostatic gradiometers (as also used in GOCE) and illustrate their different spectral behavior as well as their mutual benefit. Using simulated atom-interferometric and hybrid gradient measurements along one or more gradiometer axes in GOCE-like orbits, we determine the gravity field in spherical harmonics coefficients for the various cases and discuss the pros and cons of the selected concepts

Cold Atom Interferometry Accelerometry for Future Low-Low Satellite-to-Satellite Tracking and Cross-track Gradiometry Satellite Gravity Missions

Satellite gravity missions give unprecedented insights in the Earth system. However, a further improvement in spatial and temporal resolution is required to better monitor the various geo-processes. When considering the sensors of satellite missions, the accelerometers are the limiting factors. Cold Atom Interferometry (CAI) accelerometers are characterized by their long-term stability and an accurate knowledge of the scale factor. Closed-loop simulations are performed in order to quantify the influence of different accelerometer performances on the gravity field recovery. The impact of the scale factor knowledge on the acceleration measurement is evaluated in terms of a requirement based on the non-gravitational acceleration signal and the accelerometer noise. Furthermore, the variation of the non-gravitational acceleration signal within one interferometer cycle is studied. It is demonstrated that both aspects are significant. The impact on the acceleration measurements can be reduced to an acceptable level by drag compensation. Moreover, the addition of a CAI cross-track gradiometer to a low-low Satellite-to-Satellite Tracking mission is investigated, as supplemental observations in east-west direction are provided. This combination enhances the estimation of the high-degree coefficients and reduces the striping effects in north-south direction. We acknowledge the support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - Project-ID 434617780 - SFB 1464 and under Germany's Excellence Strategy - EXC-2123 Quantum-Frontiers - 390837967 and the support by Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR) for the projects Q-BAGS and QUANTGRAV

Cold atom interferometry accelerometry for future low-low satellite-to-satellite tracking and cross-track gradiometry satellite gravity missions

International audienc

Cold atom interferometry accelerometry for future low-low satellite-to-satellite tracking and cross-track gradiometry satellite gravity missions

International audienc

Beyond MAGIC: Evaluation of Novel Sensors and Satellite Formation Flights for Future Gravimetry Missions

For more than two decades, satellite gravimetry missions have provided unique data about mass redistribution processes in the Earth system. Ongoing climate change underlines the urgent need to continue uninterruptedly this kind of measurements with enhanced concepts and sensors. Here we focus on performance evaluation of novel accelerometers (ACC) and satellite formation flights. Only electrostatic accelerometers (EA) were utilized in satellite gravimetry missions at Low Earth Orbit (LEO) so far. EAs are one of the limiting factors in current space gravimetry dominating the error contribution at low frequencies, mostly because of the polarization wire that connects the Test Mass (TM) with the electrode housing. One focus of this study is modelling wireless enhanced EAs with laser-interferometric readout, so called "optical accelerometers" and evaluating their performance at LEOs. Contrary to present-day EAs, which measure capacitively the TM displacement and actuate it electrostatically, optical ACC, beside a similar actuation scheme, track the TM with laser interferometry. Optical accelerometry is based on promising results of LISA-Pathfinder which demonstrated the benefit of using optical ACC and UV TM discharge. This allows to sense the non-gravitational accelerations several orders of magnitude more accurate than it is realized in current gravimetry missions. Contrary to electrostatic or optical accelerometry, in Cold Atom Interferometry (CAI), atom clouds act as test masses. The unknown acceleration is calculated from the phase shift of two interfering atomic states of an atom cloud which is manipulated with pulses of two counter propagating laser beams. We model the full circle of gravimetry missions using various software parts: an orbital dynamics software, a software module, mainly developed by IGP, for modelling novel electrostatic and optical accelerometers including the major noise sources, and a software package for gravity field recovery developed at IfE. CAI and hybridized (EA+CAI) ACCs performance analyses were also carried out at IfE. In this presentation, we compare the performance of different novel accelerometers and gradiometers, i.e. enhanced electrostatic, optical, CAI and hybridized (EA+CAI), as well as demonstrate and evaluate alternative satellite formation flights and combination concepts, such as pendulum, Bender and ll-sst with cross-track gradiometry. Improved results of the recovered gravity fields, including the effect of insufficiently known background models for high-frequency mass variations, will be shown for various mission scenarios and sensors

Moho density contrast in central Eurasia from GOCE gravity gradients

Seismic data are primarily used in studies of the Earth's inner structure. Since large partsof the world are not yet sufficiently covered by seismic surveys, products from the Earth's satellite observation systems have more often been used for this purpose in recent years. In this study we use the gravity-gradient data derived from the Gravity field and steady-state Ocean Circulation Explorer (GOCE), the elevation data from the Shuttle Radar Topography Mission (SRTM) and other global datasets to determine the Moho density contrast at the study area which comprises most of the Eurasian plate (including parts of surrounding continental and oceanic tectonic plates). A regional Moho recovery is realized by solving the Vening Meinesz-Moritz's (VMM) inverse problem of isostasy and a seismic crustal model is applied to constrain the gravimetric solution. Our results reveal that the Moho density contrast reaches minima along the mid-oceanic rift zones and maxima under the continental crust. This spatial pattern closely agrees with that seen in the CRUST1.0 seismic crustal model as well as in the KTH1.0 gravimetric-seismic Moho model. However, these results differ considerably from some previously published gravimetric studies. In particular, we demonstrate thatt here is no significant spatial correlation between the Moho density contrast and Moho deepening under major orogens of Himalaya and Tibet. In fact, the Moho density contrast under most of the continental crustal structure is typically much more uniform.Funders: National Science Foundation of China (NSFC), 41429401; Czech Ministry of Education, Youth and Sport, LO1506</p