Abstact.Three gravity field models, parameterized in terms of spherical harmonic coefficients, have been computed from 71 days of GOCE (Gravity field and steady-state Ocean Circulation Explorer) orbit and gradiometer data by applying independent gravity field processing methods. These gravity models are one major output of the European Space Agency (ESA) project GOCE High-Level Processing Facility (HPF). The processing philosophies and architectures of these three complementary methods are presented and discussed, emphasizing the specific features of the three approaches. The resulting GOCE gravity field models, representing the first models containing the novel measurement type of gravity gradiometry ever computed, are analyzed and assessed in detail. Together with the coefficient estimates, full variance-covariance matrices provide error information about the coefficient solutions. A comparison with state-of-the-art GRACE and combined gravity field models reveals the additional contribution of GOCE based on only 71 days of data. Compared to combined gravity field models, large deviations appear in regions where the terrestrial gravity data are known to be of low accuracy. The GOCE performance, assessed against the GRACE-only model ITGGrace2010s, becomes superior at degree 150, and beyond. GOCE provides significant additional information of the global Earth gravity field, with an accuracy of the 2-months GOCE gravity field models of 10 cm in terms of geoid heights, and 3 mGal in terms of gravity anomalies, globally at a resolution of 100 km (degree/order 200).

Both GRACE and GOCE have proven to be very successful missions, providing a wealth of data which are exploited for geophysical studies such as climate changes, hydrology, sea level changes, solid Earth phenomena, with benefits for society and the whole world population. It is indispensable to continue monitoring gravity and its changes from space, so much so that a GRACE follow-on mission has been launched in 2018.In this paper a new satellite mission concept named MOCASS is presented, which can be considered as a GOCE follow-on, based on an innovative gradiometer exploiting ultra-cold atom technology and aimed at monitoring Earth mass distribution and its variations in time. The technical aspects regarding the payload will be described, illustrating the measurement principle and the technological characteristics of a Cold Atom Interferometer that can measure gravity gradients. The results of numerical simulations will be presented for a one-arm and a two-arm gradiometer and for different orbit configurations, showing that an improvement with respect to GOCE could be obtained in the estimate of the static gravity field over all the harmonic spectrum (with an expected error of the order of 1 mGal at degree 300 for a 5-year-mission) and that estimates are promising also for the time-variable gravity field (although GRACE is still performing better at very low degrees). Finally, the progress achievable by exploiting MOCASS observations for the detection and monitoring of geophysical phenomena will be discussed: the results of simulations of key geophysical themes (such as mass changes due to hydrology, glaciers and tectonic effects) with expected gravity change-rates, time constants and corresponding wavelengths, show that an improvement is attainable and that signals invisible to past satellites could be detected by exploiting the Cold Atom technology.

For many years the gravity field of the Earth was only seen by satellite geodesy as the main factor affecting the orbit and consequently it was retrieved together with a number of other perturbations. It is since the advent of a new generation of accelerometers that non gravitational perturbations could be separated from the gravity effects and a new era of gravity field estimates from space was born. In the preparatory work of data analysis for the new missions, performed by the geodetic community, three approaches have been proposed and numerically tested: the brute force method (direct approach), the semi analytical (time-wise) method and the space-wise method. In particular, the time-wise method takes advantage of the incoming time flow of data and, after performing a Fourier transform of the observation equations, exploits the prevailing block diagonal structure of the normal equations to estimate the harmonic coefficients of the gravity field. Complementary to it, the spacewise approach has been developed, which goes back to the traditional computation of the harmonic coefficients by some integration technique or by collocation. Some advantages and disadvantages are peculiar of both methods; particularly the space-wise approach has for long ignored the marked signature of the noise spectrum due to the specific measuring conditions of space-born accelerometers. The application of a proper Wiener filter, exploiting the correlation along the orbit, embedded into an iterative scheme seems to be the right answer. In the paper the solution of this major problem of the space-wise approach is illustrated and simulation results are discussed

No abstract

It is incontrovertible that an exchange of files is essentially required at several stages of the workflow in the architecture, engineering, and construction (AEC) industry. Therefore, investigating and detecting the capabilities/inabilities of building information modeling (BIM) software packages with respect to interoperability can be informative to stakeholders who exchange data between various BIM packages. The work presented in this paper includes a discussion on the interoperability of different software platforms commonly used in the AEC industry. Although, in theory, flawless interoperability of some types of files between different BIM platforms is ensured, in practical applications, this is not always the case. Hence, this research aims to identify faults in data exchange by assessing different possible scenarios where a sample Industry Foundation Classes (IFC) four-dimensions (4D) BIM model and related Gantt charts are exchanged. Throughout the interoperability analysis of both IFC file and Gantt charts, the following checks were carried out: geometrical and nongeometrical information exchange through IFC files, 4D information correct readability, and presence of missing schedule information in Gantt charts after their import/export procedure. The results show that interoperability between the analyzed platforms is not always ensured, providing useful insight into realistic scenarios.