4:00pm - 4:20pm
Keynote: New Missions for Improving the Terrestrial Reference Frame: Means and Impacts
The Terrestrial Reference Frame (TRF) is defined by positions and velocities of geodetic sites all around the Earth. DORIS, GNSS, SLR and VLBI techniques are used purposely to realize the TRF whose quality depends on system characteristics and processing pertinence. Mostly the TRF determination suffers from two fundamental problems: yet unrevealed systematic effects in the observations of individual space geodetic techniques and difficulties to accurately measure local ties between the system reference points.
Unfortunately these imperfections reflect on many applications, for instance any bias or drift in the TRF components propagates into the geophysical interpretations that depend on the reference frame, e.g. GIA and mean sea level variability in space and time. The global sea level rise of about 3.3 mm/yr is numerically small, but is well within the range of observational ability.
Hence one way to compensate the current TRF weaknesses is to implement all the space geodetic techniques on a same satellite platform with a very accurate determination of the radio phase centers or laser reflection point against the satellite center of mass. An on-board time unity will reduce as well some technique systematisms.
That is why different GRASP-like satellite missions have been proposed to space agencies with the aim of improving the TRF at the GGOS recommended level: accurate and stable at 1 mm and 0.1 mm/yr respectively.
The presentation aims at discussing the quality level of current TRF, at outlining the error propagation into some geophysical interpretations, at presenting the impact of GRASP-like proposed missions…
4:20pm - 4:35pm
Current Status of the GRACE Follow-On Mission
1GFZ Potsdam, Germany; 2NASA Jet Propulsion Laboratory, Pasadena, CA, United States; 3Center for Space Research, University of Texas, Austin, TX, United States
As of the time of this abstract submission, the GRACE Follow-On satellites have been constructed and transferred to Ottobrunn near Munich for several months of operational testing in the IABG test centre. The Russian/Ukrain Dnepr launcher had to be exchanged and a corresponding new contract has been signed by GFZ and Iridium Satellite LLC. This includes a "Rideshare" between GRACE-FO and 5 Iridium-Next satellites on a Space-X Falcon-9 from Vandenberg Air Force Base in California within the launch period December 2017 till February 2018.
The project team is conducting tests of satellite and instrument operation and performance and putting together updated simulations of expected performance on-orbit, including intersatellite ranging (both microwave and laser), accelerometer, thermal variability and deformation, and other errors. In addition, all required ground analysis software of the Science Data System is in development and testing at JPL, UTCSR, and GFZ, in preparation for fully integrated end-to-end (international) testing from Level-1 through Level-3 data within 2017. In this presentation, we will provide the detailed status of project integration and test, the latest simulations of science performance, and schedule for remaining project milestones.
4:35pm - 4:55pm
Keynote: Science and User Needs for Sustained Observation of Global Mass Transport by Future Gravity Field Mission Concepts
TU Munich, Germany
In an internationally coordinated initiative among the main user communities of gravity field products under the umbrella of IUGG (International Union of Geodesy and Geophysics) the science and user needs for a future gravity field mission constellation (beyond GRACE Follow-On) have been reviewed and defined. Consensus among the user communities of hydrology, ocean, cryosphere, solid Earth, and atmosphere on consolidated science requirements could be achieved. In the frame of this activity, the achievements of the first generation of dedicated gravity missions (CHAMP, GRACE, GOCE) have been discussed, and also the current limitations of these missions have been identified.
The consolidation of the user requirements became necessary, because several future gravity field studies have resulted in quite different performance numbers as a target for a future gravity mission (2025+). Based on limited number of mission scenarios, which took also technical feasibility into account, a consolidated view on the science requirements among the international user communities was derived, distinguishing between a threshold scenario and a more ambitious target scenario. Research fields that could not be tackled by current gravity missions have been identified, and the added value (qualitatively and quantitatively) of these scenarios with respect to science return has been evaluated. Beyond scientific objectives, also the societal benefit of sustained observation of the Earth’s gravity field and its temporal variation, such as operational and service applications, have been identified.
Beyond the resulting documentation, which shall form the basis for further programmatic and technological developments, this international initiative also triggered the IUGG Resolution No. 2 adopted by the IUGG Council (Prague 2015), underlining the importance of “Future Satellite Gravity and Magnetic Mission Constellations“.
In this contribution, the main results of this initiative will be presented. An overview of the specific requirements of the individual user groups, the consensus on consolidated science and user needs for observing global mass transport to understand global change and to benefit society, as well as the new research fields that have been identified during this process will be outlined and discussed. Additionally, the feasibility of the proposed mission scenarios will be analysed, focussing on the design of and double pair missions based on inter-satellite tracking, and innovative processing and gravity modelling approaches for this type of missions will be presented and discussed.
4:55pm - 5:10pm
Towards a Sustained Observing System for Mass Transport to Understand Global Change and to Benefit Society
1Delft University of Technology, Netherlands, The; 2University of Texas at Austin, USA; 3University of South Florida, USA; 4Institute de Physique du Globe de Paris, France; 5Technical University of Munich, Germany; 6University of Sheffield, United Kingdom; 7NASA Goddard Space Flight Center, USA; 8Jet Propulsion Laboratory, California, USA
The NASA and ESA space agencies established the Interagency Gravity Science Working Group (IGSWG) in 2013 to advise on future gravity mission concepts. Both NASA and ESA acknowledge the need for continued global observation of mass transport. Observing mass transport with the highest possible accuracy and spatial resolution and with temporal resolutions from daily to monthly is crucial for understanding the functioning and evolution of the Earth system (climate, geo-hazards, water cycle). Improved observation of global mass transport in terms of temporal and spatial resolution would benefit a diversity of Earth science domains (e.g. hydrology, oceanography, cryospheric sciences, solid Earth sciences, atmospheric sciences) for both scientific and application focused users, and are necessary to fully characterize diverse global change processes.
The working group finalized its activities in 2016 by delivering a report with the title "Towards a sustained observing system for mass transport to understand global change and to benefit society". This report addresses the compatibility between user requirements, constellation concepts, and expected performance. In addition, a roadmap for implementation in the post-2020 time frame is included. This roadmap defines the path towards sustained observation of mass transport with the required accuracy and spatio-temporal resolution, while addressing the need for cooperation between different space agencies and/or providers, and assessing required activities such as studies and technological developments for both the near and longer terms.
Coordinators ESA and NASA
John Labreque, Thomas Johnson, Ben Phillips (NASA)
Roger Haagmans, Luca Massotti, Christian Siemes (ESA)
5:10pm - 5:25pm
Impact of Orbit Design Choices on the Gravity Field Retrieval of Next Generation Gravity Missions - Insights on the ESA-ADDCON Project
1Technical University of Munich, Germany; 2Delft University of Technology, Netherlands; 3University of Luxembourg, Luxembourg; 4University of Stuttgart, Germany; 5European Space Agency
Next Generation Gravity Missions (NGGMs) expected to be launched in the mid-term future have set high anticipations for an enhanced monitoring of mass transport in the Earth system, establishing their products applicable to new scientific fields and serving societal needs. The European Space Agency (ESA) has issued several studies on concepts of NGGMs. Following this tradition, the project “Additional Constellations & Scientific Analysis Studies of the Next Generation Gravity Mission” picks up where the previous study ESA-SC4MGV left off.
One of the ESA-ADDCON project objectives is to investigate the impact of different orbit configurations and parameters on the gravity field retrieval. Given a two-pair Bender-type constellation, consisting of a polar and an inclined pair, choices for orbit design such as the altitude profile during mission lifetime, the length of retrieval period, the value of sub-cycles and the choice of a prograde over a retrograde orbit are investigated. Moreover, the problem of aliasing due to ocean tide model inaccuracies, as well as methods for mitigating their effect on gravity field solutions are investigated in the context of NGGMs.
The performed simulations make use of the gravity field processing approach where low-resolution gravity field solutions are co-parameterized in short-term periods (e.g. daily) together with the long-term solutions (e.g. 11-day solution). This method proved to be beneficial for NGGMs (ESA-SC4MGV project) since the enhanced spatio-temporal sampling enables a self-de-aliasing of high-frequency atmospheric and oceanic signals, which may now be a part of the retrieved signal. The potential added value of having such signals for the first time in near real-time is assessed within the project.
This paper demonstrates the preliminary results of the ESA-ADDCON project focusing on aspects of orbit design choices for NGGMs.
5:25pm - 5:40pm
GOCE and Beyond: Status and Activities
European Space Agency
This presentation provides an overview of the current status of activities in ESA related to the Gravity field and steady-state Ocean Circulation Explorer (GOCE) mission which was ESA’s first Earth Explorer in orbit between 17 March 2009 and 11 November 2013. GOCE determined geoid heights with centimetre-level accuracy and spatial variations in the static gravity field to one part per million (ppm), in both cases with a (half-wavelength) spatial resolution of 100 km on Earth’s surface. The geoid, gravity and gravity gradients of GOCE have been used for many scientific and practical applications. These related to for example to oceanography, solid Earth geophysics, aeronomy, height unification and GNSS levelling. Also more recently studies on time variations of gravity signals and ice mass balance were performed and global modelling efforts like 3D Earth were initiated. Recently, the latest, most up to date GOCE processing that led to the release 5 models has been critically reviewed and ideas for the future activities emerged. These will also be presented.