João De Teixeira da Encarnação

Delft University of Technology | TU · Department of Space Engineering (SpE)

The Next Generation Gravity Mission (NGGM), currently in a feasibility study phase as a candidate Mission of Opportunity for ESA-NASA cooperation in the frame of the Mass Change and Geo-Sciences International Constellation (MAGIC), is designed to monitor mass transport in the Earth system by its variable gravity signature with increased spatial and...

Plain Language Summary The West Antarctic Ice Sheet (WAIS) rests largely below sea level, and so is particularly vulnerable to anthropogenic climate change. The space gravimetry mission GRACE revealed that WAIS mass loss had accelerated until rapid mass loss abruptly paused in 2015. The much‐reduced rates of ice mass loss prevailed until the middle...

Although the knowledge of the gravity of the Earth has improved considerably with CHAMP, GRACE, and GOCE (see appendices for a list of abbreviations) satellite missions, the geophysical community has identified the need for the continued monitoring of the time-variable component with the purpose of estimating the hydrological and glaciological year...

In preparation for the Center for Space Research Release 6 of Gravity Recovery and Climate Experiment (GRACE) data, 32 accelerometer parameterization schemes are analyzed, which combine skew-symmetric, symmetric, and full-scale matrices with four different bias parameterizations inspired on those used on Release 5. After three selection stages, it...

Although the knowledge of the gravity of the Earth has improved considerably with CHAMP, GRACE and GOCE satellite missions, the geophysical community has identified the need for the continued monitoring of the time-variable component with the purpose of estimating the hydrological and glaciological yearly cycles and long-term trends. Currently, the...

We demonstrate that the Swarm mission serves as an interesting source of global gravimetric data to fill gaps and periods not covered by the GRACE and GRACE-FO missions, be it with reduced spatial resolution. We illustrate that major geophysical signals that take place during such periods can be observed by Swarm at regional scales. For the first 5...

This report validates the combined gravity field models produced on the context of the Multi-approach Gravity Field Models from Swarm GPS data project. We describe the approach for combining individual gravity field solutions (i.e. those produced by the various partners) and validate of the combined models by comparing them with GRACE.

This Technical Note presents processing details of the kinematic orbits and gravity field estimation approachea, as well as data format specifications. Find this document at: https://earth.esa.int/web/guest/missions/esa-eo-missions/swarm/activities/scientific-projects/disc#MAGF

Since 2013, the Swarm satellite constellation has allowed us to observe the Earth’s large-scale mass transport processes. We present the nearly complete time series of monthly gravity field models derived from the data collected by Swarm’s GPS receivers, from December 2013 to September 2018. These models are the result of the combination of four in...

The United States and Germany (NASA and GFZ) joint GRACE (Gravity Recovery And Climate Experiment) Follow-On (FO) twin-satellite mission has been successfully launched on May 22, 2018, to continue the climate data record collected by the successful GRACE mission which ceased operation on July 2017, with the GRACE instrument and its data degraded mu...

This Technical Note intends to: i) provide guidelines for GPS data screening or weighting strategies to efficiently mitigate ionosphere-induced artifacts in the gravity field; ii) recommend the inclusion of measured or modelled non-gravitational accelerations in the production of the gravity field models (WP421 to WP424); and iii) conclude on the a...

Since April 2011, the thermal control of the accelerometers on board the GRACE satellites has been turned off. The time series of along-track bias clearly show a drastic change in the behaviour of this parameter, while the calibration model has remained unchanged throughout the entire mission lifetime. In an effort to improve the quality of the gra...

The Swarm satellites continue to provide high-quality hl-SST data. We use these data to derive the time-varying gravity field of the Earth at 1500km resolution, on a monthly basis since December 2013. We combine the gravity field solutions computed with the data of all three satellites, as provided by the Astronomical Institute (ASU), Astronomical...

The Swarm satellite mission provides important information regarding the temporal changes of Earth’s gravity field. Several European institutes routinely process Swarm GPS data to produce kinematic orbits, which forms the basis for the estimation of monthly gravity fields. Each institute follows a different gravity field estimation approach and all...

The Swarm satellites were launched on November 22, 2013, and carry accelerometers and GPS receivers as part of their scientific payload. The GPS receivers do not only provide the position and time for the magnetic field measurements, but are also used for determining non-gravitational forces like drag and radiation pressure acting on the spacecraft...

It is of great interest to numerous geophysical studies that the time series of global gravity field models derived from Gravity Recovery and Climate Experiment (GRACE) data remains uninterrupted after the end of this mission. With this in mind, some institutes have been spending efforts to estimate gravity field models from alternative sources of...

The Earth’s Magnetic Field and Environment Explorers (Swarm), launched in November 2013, aim at improving the knowledge of the geomagnetic field. Nevertheless, the data gathered by the Global Positioning System (GPS) and star tracker instruments are also useful for geodetic applications, in particular to measure large-scale temporal variations of E...

The GPS instruments on-board the three Earth’s Magnetic Field and Environment Explorer (Swarm) satellites provide the opportunity to measure the gravity field model at basin-wide spatial scales. In spite of being a geo-magnetic satellite mission, Swarm’s GPS receiver collects highly accurate hl-SST data (van den IJssel et al., 2015), which has been...

Since 2002 Gravity Recovery and Climate Experiment (GRACE) provides monthly gravity fields from K-band ranging (KBR) between two GRACE satellites. These KBR gravity monthlies have enabled the global observation of time-varying Earth mass signal at a regional scale (about 400 km resolution). Apart from KBR, monthly gravity solutions can be computed...

The Swarm satellites were launched on November 22, 2013, and carry accelerometers and GPS receivers as part of their scientific payload. The GPS receivers do not only provide the position and time for the magnetic field measurements, but are also used for determining non-gravitational forces like drag and radiation pressure acting on the spacecraft...

The project European Gravity Service for Improved Emergency Management (EGSIEM) of the Horizon 2020 Framework Programme for Research and Innovation of the European Commission has started in January 2015. EGSIEM shall demonstrate that observations of the redistribution of water and ice mass derived from the current GRACE mission, the future GRACE-FO...

SWARM is an ESA mission of three satellites to study the geomagnetic field, each equipped with a GPS receiver, which were successfully placed in orbit in November 2013. Over the year 2014, there were several changes in the processing of Swarm GPS data that improved the quality of obtained gravity field solutions. Although the accuracy and resolutio...

We present the results of a study of the impact of orbit positioning noise (OPN) caused by incomplete knowledge of the Earth’s gravity field on gravity models estimated from satellite gravity data. The OPN is simulated as the difference between two sets of orbits integrated on the basis of different static gravity field models. The OPN is propagate...

The main objective of the thesis is to identify the optimal set-up for future satellite gravimetry missions aimed at monitoring mass transport in the Earth’s system.The recent variability of climatic patterns, the spread of arid regions and associ- ated changes in the hydrological cycle, and vigorous modifications in the ice coverage at polar regio...

The European Space Agency (ESA) Swarm mission was launched on 22 November 2013 to study the dynamics of the Earth’s magnetic field and its interaction with the Earth system. The mission consists of three identical satellites, flying in carefully selected near polar orbits. Two satellites fly almost side-by-side at an initial altitude of about 480 k...

Temporal aliasing is expected to add up to the error budget of future gravity satellite missions of low-low satellite-to-satellite tracking (LL-SST) type in such a way, that could act as a constraining factor on their way to achieve the expected accuracy that new generation sensors could provide. Within the scope of the ESA-SC4MGV project, we inves...

The three-satellite ESA Swarm mission aims at mapping the Earth’s global geomagnetic field at unprecedented spatial and temporal resolution and precision. Swarm also aims at observing thermospheric density and possibly horizontal winds. Precise orbit determination (POD) and Thermospheric Density andWind (TDW) chains form part of the Swarm Constella...

The ability of satellite gravimetry data to validate global static models of the Earth's gravity field is studied. Two types of data are considered: K-band ranging (KBR) data from the Gravity Recovery and Climate Experiment (GRACE) mission and Satellite Gravity Gradiometry (SGG) data from the GOCE (Gravity field and steady-state Ocean Circulation E...

Swarm, a three-satellite constellation to study the dynamics of the Earth’s magnetic field and its interactions with the Earth system, is expected to be launched in late 2013. The objective of the Swarm mission is to provide the best ever survey of the geomagnetic field and its temporal evolution, in order to gain new insights into the Earth system...

In the framework of the ESA GOCE+ project, we are developing algorithms to retrieve thermospheric densities and crosswind speeds from GOCE observations. The resulting data on the thermosphere will complement and extend existing thermosphere datasets, such as those derived from CHAMP and GRACE data. The data processing and the resulting data set are...

The goal of this study is to help define the precise positioning requirements needed to observe time-variable gravity with the upcoming Iridium NEXT satellite constellation. Various sources of orbit error that might be expected for the Iridium NEXT satellites are discussed, and a simulation study exploring the impact of these errors on the expected...

The ability to measure temporal gravity field variations is of great interest to the Earth sciences community. These gravity measurements provide a unique source of information about Earth's mass transport processes, such as ocean currents, sea-level change, atmospheric variations, continental hydrology, movements of the solid earth, and the flux o...

A comprehensive study has been carried out to possible future gravity field missions or Next Generation Gravity Missions (NGGM). The study team was led by Thales Alenia Space (TAS) and included both industrial partners and scientific institutes, where the latter were coordinated by DEOS. The study covered all aspects from science requirements, sens...

Gravity Recovery And Climate Experiment (GRACE) satellite mission shows a somewhat worse performance than the baseline one, which was defined at the mission design phase. A common opinion is that this quality degradation is caused by a lack of knowledge about rapid mass transport processes (for instance, atmospheric pressure changes), so that the c...

Gravity Field and Steady-State Ocean Circulation Explorer is a satellite gravimetry mission launched in 2009 in order to measure the Earth's gravity field and geoid with an unprecedented accuracy and spatial resolution. To that end, the GOCE satellite is equipped with a unique Satellite Gravity Gradiometer (SGG) that measures (primarily) diagonal e...

Spectral analysis of data noise is performed in the context of gravity field recovery from inter-satellite ranging measurements acquired by the satellite gravimetry mission GRACE. The motivation of the study is two-fold: (i) to promote a further improvement of GRACE data processing techniques and (ii) to assist designing GRACE follow-on missions. T...

The spatiotemporal resolution of the time-variable gravity field models derived from current dedicated gravity field missions is inherently limited by their ground-track coverage. Furthermore, the results are subject to aliasing effects caused by submonthly mass transport signals, such as those caused by atmospheric and ocean processes. To address...

This study explores the feasibility of using satellite constellations to improve the determination of Earth's time variable gravity field. Current dedicated gravity field missions such as GRACE have provided valuable observations of the global gravity field; however, as single satellites (or satellite pair in the case of GRACE), their ground track...

The satellite gravity mission GRACE (Gravity Recovery And Climate Experiment), which was launched in 2002, offers a unique opportunity to monitor tiny variations of the Earth's gravity and associated mass transport from space. In particular, the redistribution of water in the Earth's system can be traced in this way, which is critical for monitorin...

The data acquired by the KBR (K-Band Ranging) system on board the GRACE (Gravity Recovery And Climate Experiment) satellites is currently a valuable source of information for recovery of static and dynamic parts of the Earth's gravity field (particularly, at the global scale). To derive the static part, sufficiently long data spans are needed. On t...

This study will assess the feasibility of using a constellation of non-dedicated satellites to determine Earth's time-variable gravity field. Precise orbit data from the FORMOSAT-3/COSMIC satellite constellation will be processed and the results will be compared to theoretical predictions. Provided accurate knowledge of the satellite orbits through...

The monitoring of Earth's gravity field from space has witnessed great progress through the launch of several dedicated satellite missions over the past decade, but the mission life times for all of these missions are projected to end within the next five years. Looking forward to potential follow-on missions, there are limitations in the current g...

Temporal variations of the Earth’s gravity field are traditionally represented with a set of spherical harmonic coefficients derived once per month. In practice, however, the gravity field changes continuously (e.g. because of on-going hydrological processes). This discrepancy causes temporal aliasing which manifests itself as errors in the obtaine...

A thermal laser thruster depends on introduction of a high energy laser beam, absorption by the fluid propellant, confinement of the hot propellant gas with minimal losses, and conversion of thermal to kinetic energy in the nozzle. Based on thermodynamic constraints, efficient energy conversion is possible in either the subsonic Laser Supported Com...

Ground to orbit launch using laser propulsion requires a thermal system. Physically allowed thermal concepts are discussed and compared. It is argued that the laser supported detonation (LSD) mechanism presents a number of advantages over the alternatives. Numerical simulations of ascent trajectories for a system based on the LSD mechanism were per...

It is widely known that producing a single stage to orbit spacecraft is no easy task. It is also understood that it will be the first steady step towards spacecraft that operate in much the same way as today's airliners. This, in turn is believed to decrease the economical cost of reaching space through more efficient use of a single vehicle and hi...