Testing General Relativity with Satellite Laser Ranging: Recent Developments

In this paper the most recent developments in testing General Relativity in the gravitational field of the Earth with the technique of Satellite Laser Ranging are presented. In particular, we concentrate our attention on some gravitoelectric and gravitomagnetic post--Newtonian orbital effects on the motion of a test body in the external field of a central mass.Comment: Latex2e, 10 pages, no figures, no tables. Paper presented at COSPAR2002 conference held in Houston, TX, from 10 October 2002 to 19 October 2002. To appear in Advance in Space Research. References added and update

Development of the TanDEM-X Calibration Concept: Analysis of Systematic Errors

The TanDEM-X mission, result of the partnership between the German Aerospace Center (DLR) and Astrium GmbH, opens a new era in spaceborne radar remote sensing. The first bistatic satellite synthetic aperture radar mission is formed by flying the TanDEM-X and TerraSAR-X in a closely controlled helix formation. The primary mission goal is the derivation of a high-precision global digital elevation model (DEM) according to High-Resolution Terrain Information (HRTI) level 3 accuracy. The finite precision of the baseline knowledge and uncompensated radar instrument drifts introduce errors that may compromise the height accuracy requirements. By means of a DEM calibration, which uses absolute height references, and the information provided by adjacent interferogram overlaps, these height errors can be minimized. This paper summarizes the exhaustive studies of the nature of the residual-error sources that have been carried out during the development of the DEM calibration concept. Models for these errors are set up and simulations of the resulting DEM height error for different scenarios provide the basis for the development of a successful DEM calibration strategy for the TanDEM-X mission

LAGEOS-type Satellites in Critical Supplementary Orbit Configuration and the Lense-Thirring Effect Detection

In this paper we analyze quantitatively the concept of LAGEOS--type satellites in critical supplementary orbit configuration (CSOC) which has proven capable of yielding various observables for many tests of General Relativity in the terrestrial gravitational field, with particular emphasis on the measurement of the Lense--Thirring effect.Comment: LaTex2e, 20 pages, 7 Tables, 6 Figures. Changes in Introduction, Conclusions, reference added, accepted for publication in Classical and Quantum Gravit

Estimating the decay rates of orbital debris through upper-atmosphere density data supplemented with on-board accelerometer measurements

This thesis is focused on research of an accurate method to compute atmospheric density. It presents a comparison between data calculated by MSISE-90 model and ones obtained by the accelerometers on-board of GRACE. It describes a possible new satellite METRIC, which has, as goal, the improve of density data in upper atmoshpere to have better estimate of air drag and, consequently, of satellite operative life.ope

Short Report of IVS Working Group 5 (WG5) on Space Science Applications - An IVS Perspective

No abstract availabl

Simulated Satellite Formation Flights for Detecting the Temporal Variations of the Earth’s Gravity Field

In this thesis, the concept of satellite formation flight (SFF) is studied by means of simulated satellite observations. With various formation types enabling inter-satellite measurements in various directions (e.g. along-track, cross-track or radial), the principal tasks in global gravity field recovery are tackled: the determination of the static gravity field and the detection of its temporal variations. The investigated formation flight types include GRACE, Pendulum, GRACE-Pendulum, Radial wheel and Inclined wheel configurations. For each formation type, appropriate orbit parameters are determined to receive homogeneous subsatellite track patterns required for a high spatial resolution. In addition, orbit designs are developed which allow an enhancement of the temporal resolution (i.e. sub-month solutions). The investigated formation flight types of this case include GRACE-24days, GRACE-12days, Multi-GRACE ΔM and Multi-GRACE ΔΩ configurations. In the static gravity field analysis, the test scenarios cover different spectral ranges of the Earth’s gravity field up to the spherical harmonics degree 180. The detection of the temporal variations is performed using physical models from ocean tides, atmosphere, ocean and continental hydrology. The numerical computations show that significant improvements are achieved from the formation flights for the recovery of the global static gravity field and the detection of its temporal variations. Thus, the study provides an outlook on the progress in the gravity field modeling that is achievable by future satellite missions.Simulierte Satellitenformationsflüge zur Bestimmung der temporalen Variationen des Erdgravitationsfeldes In der vorliegenden Arbeit wird mit Hilfe simulierter Satellitenbeobachtungen das Konzept des Satellitenformationsflugs (SFF) untersucht. Mit verschiedenen Formationstypen, mit denen Intersatellitenmessungen in verschiedenen Richtungen gesammelt werden können (z.B. along-track, cross-track oder radial), werden die beiden wesentlichen Aufgaben der globalen Gravitationsfeldbestimmung bearbeitet, die Bestimmung des statischen Gravitationsfeldes und die Bestimmung seiner zeitlichen Variationen. Die untersuchten Formationstypen umfassen GRACE, Pendulum, GRACE-Pendulum, Radial wheel and Inclined wheel Konfigurationen. Für jeden Formationstyp werden geeignete Bahnparameter ermittelt, um die für eine hohe räumliche Auflösung notwendige gleichmäßige Überdeckung der Erde mit Subsatellitenbahnen zu erreichen. Außerdem werden Formationsdesigns entworfen, die eine Verbesserung der zeitlichen Auflösung erlauben (submonatliche Lösungen). Die untersuchten Formationstypen dieses Falls umfassen GRACE-24days, GRACE-12days, Multi-GRACE ΔM und Multi-GRACE ΔΩ Konfigurationen. Bei der Bestimmung des statischen Schwerefeldes werden den Testszenarien unterschiedlich hoch aufgelöste Feldmodelle bis Grad 180 der Kugelfunktionsentwicklung zugrunde gelegt. Die Simulation der zeitlichen Variationen erfolgt mit physikalischen Modellen für die Ozeangezeiten, für die Massenverlagerungen in Atmosphäre und Ozeanen und für die kontinentale Hydrologie. Die numerischen Untersuchungen zeigen, dass signifikante Verbesserungen sind von Satellitenformationsflügen zur Bestimmung des statischen Gravitationsfeldes und der Bestimmung seiner zeitlichen Variationen erreicht. Die Arbeit liefert damit einen Ausblick auf den Fortschritt in der Gravitationsfeldbestimmung, der mit zukünftigen Satellitenmissionen möglich sein wird

Comparison of accelerometer data calibration methods used in thermospheric neutral density estimation

Ultra-sensitive space-borne accelerometers on board of low Earth orbit (LEO) satellites are used to measure non-gravitational forces acting on the surface of these satellites. These forces consist of the Earth radiation pressure, the solar radiation pressure and the atmospheric drag, where the first two are caused by the radiation emitted from the Earth and the Sun, respectively, and the latter is related to the thermospheric density. On-board accelerometer measurements contain systematic errors, which need to be mitigated by applying a calibration before their use in gravity recovery or thermospheric neutral density estimations. Therefore, we improve, apply and compare three calibration procedures: (1) a multi-step numerical estimation approach, which is based on the numerical differentiation of the kinematic orbits of LEO satellites; (2) a calibration of accelerometer observations within the dynamic precise orbit determination procedure and (3) a comparison of observed to modeled forces acting on the surface of LEO satellites. Here, accelerometer measurements obtained by the Gravity Recovery And Climate Experiment (GRACE) are used. Time series of bias and scale factor derived from the three calibration procedures are found to be different in timescales of a few days to months. Results are more similar (statistically significant) when considering longer timescales, from which the results of approach (1) and (2) show better agreement to those of approach (3) during medium and high solar activity. Calibrated accelerometer observations are then applied to estimate thermospheric neutral densities. Differences between accelerometer-based density estimations and those from empirical neutral density models, e.g., NRLMSISE-00, are observed to be significant during quiet periods, on average 22 % of the simulated densities (during low solar activity), and up to 28 % during high solar activity. Therefore, daily corrections are estimated for neutral densities derived from NRLMSISE-00. Our results indicate that these corrections improve model-based density simulations in order to provide density estimates at locations outside the vicinity of the GRACE satellites, in particular during the period of high solar/magnetic activity, e.g., during the St. Patrick's Day storm on 17 March 2015

Remote Sensing by Satellite Gravimetry

Over the last two decades, satellite gravimetry has become a new remote sensing technique that provides a detailed global picture of the physical structure of the Earth. With the CHAMP, GRACE, GOCE and GRACE Follow-On missions, mass distribution and mass transport in the Earth system can be systematically observed and monitored from space. A wide range of Earth science disciplines benefit from these data, enabling improvements in applied models, providing new insights into Earth system processes (e.g., monitoring the global water cycle, ice sheet and glacier melting or sea-level rise) or establishing new operational services. Long time series of mass transport data are needed to disentangle anthropogenic and natural sources of climate change impacts on the Earth system. In order to secure sustained observations on a long-term basis, space agencies and the Earth science community are currently planning future satellite gravimetry mission concepts to enable higher accuracy and better spatial and temporal resolution. This Special Issue provides examples of recent improvements in gravity observation techniques and data processing and analysis, applications in the fields of hydrology, glaciology and solid Earth based on satellite gravimetry data, as well as concepts of future satellite constellations for monitoring mass transport in the Earth system