Lasers and Ultracold Atoms for a Changing Earth

Applying new technology rooted in quantum mechanics and relativity to terrestrial and space geodesy will sharpen our understanding of how the planet responds to natural and human-induced changes.

Monitoring critical infrastructure and anthropogenic hazards in Malaga province (southern Spain) using SAR remote sensing

<p>Land surface is in constant motion due to both natural causes and human activity. Over time, many measurement techniques have been developed to study the deformation of the earth's surface. Some of them, despite having different levels of accuracy, are slow and time consuming (e.g., classical geodetic techniques). The introduction of space geodesy techniques such as GNSS systems and SAR remote sensing have offered new opportunities for precision deformation control in the field of space geodesy. In particular, using satellite radar interferometry (InSAR) as an Earth Observation routine technique, the deformation of large areas of the terrain can be monitored providing displacements at a relatively low cost compared with other ground-based techniques. Nowadays, we are living in the golden age of InSAR as there has never been as much SAR data from different missions as there is today. Of particular importance is the Copernicus program of the European Commission and ESA, which provides us with an inexhaustible source of free SAR data with extraordinary potential for monitoring the earth's surface thanks to the constellation of Sentinel-1 SAR satellites. Thanks to the great capability of SAR remote sensing, many civil infrastructures can be monitored and inspected from space without the need for physical intervention on the ground, greatly reducing costs and execution time. The advanced InSAR time series algorithms allow us to investigate the displacements of these infrastructures with uncertainties of the order of 1 mm/year, interpreting time series of interferometric phases at coherent point reflectors (PS). The use of C-band SAR data from ERS-1/2, Envisat, and Sentinel-1 has allowed us to monitor the southeast of the province of Málaga in southern Spain during the last thirty years, obtaining a deformation pattern of some critical infrastructures in the area. We can highlight, among them: the Limonero dam inaugurated in 1983, whose reservoir regulates the avenues of the Guadalmedina river and serves as a water supplying source for the city of Malaga; the Málaga-Costa del Sol international airport, an important airport for Spanish tourism as it is the main airport serving the Costa del Sol; the Málaga harbor, an industrial area, or some roads and railways. Of special importance is an urban sector with an intensive overexploitation of aquifers. Due to the increase in population because of the expansion of the tourism industry in the Benalmádena coast and Torremolinos area, the aquifers are being affected after the intensive overexploitation of groundwater with the consequent subsidence of the terrain, continuous and increased over time. In this contribution, we show our results of the SAR remote sensing application in this area of the southern Spanish coast.</p>

Exploring LEO cube satellite technology for space geodesy: SLR-VLBI POD in the GGOS era

<p>With test satellites already in space, the Swiss company Astrocast is currently in the process of establishing a constellation of about 80 nanosatellites for commercial purposes that are operating in a low Earth orbit (LEO). As a result of the collaboration with ETH Zürich, such satellites will be equipped with both low-cost multi-GNSS dual-frequency receivers and a small array of laser retroreflectors for satellite laser ranging (SLR). In the future, this set of geodetic instruments could be also extended with a simple, compact and low-power transmitter compliant with the next-generation very long baseline interferometry (VLBI) system, known as the VLBI Global Observing System (VGOS). Therefore, apart from scientific studies based on such state-of-the-art multi-GNSS receivers in space, the Astrocast nanosatellite network could also be examined in terms of satellite co-locations. In this case, the new geometrical connections in space could be realized together with all ground-based instruments that can observe the co-location satellites. Assuming sufficient precision of such observations and good knowledge of the spacecraft environment, this approach could result in an enhanced quantity of tie measurements at a high spatio-temporal resolution, potentially leading also to an enhanced quality of common geodetic parameters. However, accurate orbit determination is of high importance, whenever considering potential co-location in space or, in general, estimating various global parameters of geophysical interest.<br>In this contribution, we focus on precise orbit determination (POD) of LEO Astrocast-type nanosatellites based on global SLR-only, VGOS-only as well as combined SLR-VGOS observations. The impact of this concept on various geodetic parameters and the derived orbits is studied on the basis of Monte-Carlo simulations carried out with the c5++ analysis software. All simulated data are combined on the observation level and used to derive satellite orbits and to estimate both, station-based and global geodetic parameters. Our study is based on VGOS-type schedules created in VieSched++ and consisting of both quasar and satellite observations. In addition to the simulated laser measurements to Astrocast satellites, the SLR-related solutions include also global observations to LAGEOS-1/2 satellites. Our considerations involve solutions with different time intervals, satellite observation precision levels and quantity of the considered cube satellites, providing thus initial insights concerning prospective utilization of LEO cube satellite technology for space geodesy in the era of the Global Geodetic Observing System.</p>

Consistent Weather-Dependent Corrections for Space Geodesy; Validation via GNSS and VLBI Analysis

<p align="justify"><span>W</span><span>hether utilizing consistent models to describe weather-dependent effects on geodetic observations or a collection of models that yield accurate results individually, has </span><span>remained an unanswered question in space geodesy. </span><span>We study the superimposed effect of atmospheric refraction and environmental loading on GNSS and VLBI data analysis. Variable atmospheric refraction and site displacements induced by non-tidal geophysical loading constitute a large contribution to the modern space geodetic data analysis error budget. State-of-the-art weather models such as ECMWF‘s operational analysis and the atmospheric reanalysis ERA5 have proven to be an accurate forcing data set to drive relevant measurement corrections. Since the effects of these phenomena (refraction and loading) on geodetic observables exhibit non-trivial correlations with each other at a multitude of spatio-temporal scales, employing inconsistent data sets may deteriorate the geodetic results, such as the station coordinates and the Earth rotation parameters. The purpose of this contribution is twofold: (i) present our strategy towards consistent weather-dependent models and explore the merits stemming from the adoption thereof, and (ii) evaluate atmospheric delay and geophysical loading models consistently derived from ERA5 via the reanalysis of GNSS and VLBI data. To identify the extent to which the application of inconsistently forced reduction models causes discrepancies in the geodetic adjustment, we carried out a series of Monte Carlo runs. GNSS and VLBI observations were simulated employing ERA5-driven data (ray-traced delays and loading displacements), but reduced by applying a version thereof subjected to systematic and random noise driven from the performance of state-of-the-art models, at the observation equation level. To evaluate the model coupling with real data, we conduct a GNSS and VLBI repro and compare our new solutions to the GFZ‘s contribution to ITRF2020.</span></p>

Twelve Years of High Frequency Absolute Gravity Measurements at the UK’s Space Geodesy Facility: Systematic Signals and Comparison with SLR Heights

Absolute gravity measurements taken on a near-weekly basis at a single location is a rarity. Twelve years of data at the UK’s Space Geodesy Facility (SGF) provides evidence to show that the application of results from international comparisons of absolute gravimeters should be applied to data and are critical to the interpretation of theSGF gravity time series of data from 2007 to 2019. Though residual biases in the data are seen. The SGF time series comprises near weekly data, with exceptions for manufacturer services and participation in international instrument comparisons. Each data set comprises hourly data taken over 1 day, with between 100 and 200 drops per hour. Environmental modelling indicates that the annual groundwater variation at SGFof some 2 m influences the gravity data by 3.1 μGal, based upon some measured and estimated soil parameters. The soil parameters were also used in the calculation of the effect of an additional telescope dome, built above the gravity laboratory, and have been shown to be realistic. Sited in close proximity to the long-established satellite laser ranging (SLR) system and the global navigation satellite systems (GNSS) the absolute gravimetry (AG) measurements provide a complimentary geodetic technique, which is non space-based. The SLR-derived height time series provides an independent measurement of vertical motion at the site which may be used to assess the AG results, which are impacted by ground motion as well as mass changes above and below the instruments.

Plate and faults boundary detection using gravity disturbance and Bouguer gravity anomaly from space geodesy

Nowadays, satellite technology has developed significantly. Geodesy satellites such as Grace and Grace-FO can be used for subsurface mapping. The mapping is in the form of detection of the plate details, faults, and regional geodynamic conditions. This study aims to detect plate and faults from space geodesy using the gravity disturbance and Bouguer gravity anomaly parameter. The study area is in the Sunda Strait. Gravity disturbance is one of the gravity model parameters. Gravity disturbance is the gravitational potential of the topography expressed by the spherical harmonic model and the topographic effect by Barthelmes's calculations. Gravity disturbance can visualize subsurface conditions. Bouguer gravity anomaly is needed to get the condition on subsurface objects. This parameter visualizes subsurface conditions in the form of rocks and non-rocks. These conditions can distinguish oceanic crust and continental crust. Gravity contours are needed to obtain plate and faults predictions. The results obtained are validated patterns and shapes with plate and faults secondary data. The tolerance used in this validation is 80%. The gravity disturbance parameter obtained a value of 83% in verifying the accuracy of assessment in plate and faults detection. The Bouguer gravity disturbance parameter obtained a verification value of accuracy assessment in plate detection but 65% in faults detection. This accuracy assessment uses pattern and texture parameters in detecting the similarity of two or more images. This plate and faults detection results are more detailed and can be used for geophysical, geological, earthquake, and earth dynamics applications.