G21C-01
The GRACE Mission: Status and Future Prospects
The mass transport between the earth's atmosphere, oceans and solid earth is a critical component of global climate change processes and is an important component of the signals associated with global sea level and polar ice mass change, depletion and recharge of continental aquifers, and change in the deep ocean currents. This mass exchange has a gravitational signal, which can be monitored as an indication of the mass exchange process. The Gravity Recovery and Climate Experiment (GRACE) is a joint NASA and DLR mission whose purpose is to improve our understanding of the Earth's dynamical system by making pioneering measurements of the gravity signals associated with mass exchange between its components. The twin satellites involved in the GRACE mission were launched on March 17, 2002 and initiated scientific measurements in May 2002. The mission completed a six-year measurement sequence in March 2008. During this interval, GRACE has provided an accurate measurement of the time-variability and long-term mean mass distribution of the Earth's dynamic system. During the six-year interval, GRACE has provided global measurements of mass flux between the land, ocean, atmosphere and the cryosphere with un-precedented detail and accuracy. In this presentation, we will summarize the state of the GRACE mission, and describe plans for the coming years. We will survey the state of the multi-disciplinary science applications of the GRACE mission that are conducted in conjunction with various satellite missions (TOPEX/Poseidon, Jason-1, ICESat, GOCE) and discuss the scientific concerns for a Grace Follow-on Mission.
G21C-02 INVITED
GOCE: Status Shortly After Launch
Since September this year GOCE is in orbit. Its objective is the measurement of the Earth's gravity field and geoid with high precision and spatial resolution. One of its primary goals is the determination of the global surface ocean circulation, in conjunction with more than 15 years of satellite altimetry data. Ocean circulation and derived from it ocean transport and sea level change are key parameters in climate modelling. GOCE will also to contribute to solid Earth physics, geodesy and surveying. GOCE is unique in several ways. It carries the first satellite gravity gradiometer. This very delicate instrument consists of three orthogonal pairs of high precision accelerometers. The measurement principle is differential accelerometry. Its orbit altitude is less than 270 km. It is kept in this low orbit free of drag by active drag compensation in flight-direction. Attitude control is done by magnetic torquers. Stiff carbon sandwich material and temperature stabilization prevent gravitational noise from the spacecraft. The presentation will inform about the status of the mission in terms of science data processing and data quality.
G21C-03
GOCE: Initial In-Orbit Experience
By the time of the Fall Meeting the GOCE mission is expected to have been in orbit for a couple of months.
This paper describes the initial in-orbit experience with the satellite and its instrumentation, focussing on the
commissioning and calibration activities. Also described are the first data processing efforts, including a very
preliminary estimate of the data quality. GOCE is launched by a Rockot launch vehicle into a 96.7°
sun-synchronous orbit of 280 km altitude from which it will decay down to an initial measurement altitude of
263 km. The satellite will map the Earth's gravity field at unprecedented spatial resolution and accuracy for
about 20 months (nominal mission).
http://www.esa.int/goce
G21C-04 INVITED
Future Prospects and Plans for Improved GRACE Data Products
The GRACE RL04 gravity field data products from UTCSR, GFZ and JPL have been available to the user
community for more than 18 months. In this time, we have reached a better understanding of the quality of
these products, and its connection to the quality and attributes of the input data and background models
used in earlier data processing. In this paper, we will summarize the important lessons learnt in the recent
past in this respect. We will describe the planned upgrades to the quality and attributes of the Level-1B and
Level-2 data products. The re-processing for Release-05 is planned for early 2009, and we will discuss the
readiness status for this new release.
http://www.csr.utexas.edu/grace
G21C-05
Towards GFZ EIGEN-GRACE06S Gravity Field Time Series
GFZ as part of the GRACE Science Data System has processed almost the complete GRACE mission data. The resulting time series of nearly 70 monthly gravity field solutions is called EIGEN-GRACE05S (or RL04 in the SDS nomenclature) and depicts various time-varying mass variation signals in the system Earth such as the continental hydrological cycle, ice mass change in Antarctica and Greenland or the Sumatra Earthquake in December 2004. Because unfortunately, the error level of EIGEN-GRACE05S is still about a factor of 15 above the pre-launch simulated baseline accuracy, we are going to reprocess all data with improved background models and processing standards. The presentation will focus on existing ideas for the improvement of RL05 and their benefits.
G21C-06
Global and Regional Mass Flux Solutions from GRACE KBRR Data Based on Various Treatments of Spherical Harmonic Coefficients Including Mascons
We examine various approaches to gain increased temporal and spatial resolution in mass flux estimates made from spherical harmonic solutions based on GRACE K-band range rate (KBRR) data. Although some of the solutions we present use standard post-solution smoothing and averaging techniques, our study focuses only on techniques applied at the solution stage (during the estimation process). The advantage of forward modelling of known signals from hydrology and glacial isostatic adjustment (GIA) are examined. Regional and possibly global solutions made from lumped spherical harmonics (mascons) are also examined.
G21C-07
Reiteration of GRACE data processing at CNES/GRGS
The GRACE mission, already more than 6 years in operation, has provided a large-scale vision of temporal gravity variations on the Earth surface. It is presently profitable to entirely reprocess the GRACE data thanks to more accurate a priori models as well as improved computation strategies. In this context the CNES/GRGS team has undertaken a full reiteration of the GRACE and LAGEOS data processing, based on upgraded models for generating: 1) a time-series of truly 10-day gravity field models from spherical harmonic degree 1 to 50 and 2) a static satellite-only gravity field model up to degree and order 160, but in which annual and semi-annual periodic components as well as drift are modelled up to degree 30. In addition, tidal coefficients for long period, diurnal and semi-diurnal waves have been adjusted as well in order to minimize aliasing effects. The adjusted tide constituents were selected based on a sensitivity analysis using the GRACE orbit parameters and the precision of the KBR instrument. Strategy, results and validations of this reiteration (which is made available on the http://bgi.cnes.fr web site) will be presented. In particular, the problem of geoid signal attenuation due to constraining the solutions will be addressed.
G21C-08
Analysis of GRACE Solutions: Implications for Large Scale Global Change Results
We continue to utilize our capability to perform comprehensive spherical harmonic and mascon solutions to compare and contrast the effects of the selected solution basis function and of the range of plausible analyst choices in terms of specific solution parameterization (spatial resolution, nuisance parameters, etc). We have been successful this year in identifying and understanding, for the first time, several weakly determined solution characteristics (especially at the long-mid spatial scales) of both harmonic and mascon solutions from GRACE, the understanding of which can have significant impact on mass change estimates derived from either method. We will discuss these sensitivities, how they map into oceanic and ice mass solutions, and how we recommend handling them in future GRACE data releases. In addition, we will summarize several new aspects of the next generation of JPL GRACE gravity data (Release 5), including ocean tide model, GPS receiver and transmitter phase center maps, and other improvements.