B.1 - Interdisciplinary Topics
(Convener: Srinivas Bettadpur)

The Geodetic Reference Antenna in Space (GRASP) - A Mission to Enhance the Terrestrial Reference Frame
(Nerem, Bar-Sever and GRASP Team)

Mass Transport and Climate Variability: Insights via GRACE
(Dickey, de Viron)

Inversion of Multiple Data Sets and GRACE's Contribution to Global Geodesy
(Wu, Colileux, Altamimi, Vermeersen, Gross, Fukumori)

Water and temperature control of Vegetation productivity in Eurasia
(Tong, Velicogna, Kimball)

Hydrological Behavior and Potential Land-Use Impacts in the Central Brazilian Savanna Biome: Preliminary Results from GRACE, TRMM, and MODIS
(Fereira, Bettadpur, Coe, Costa)

Session: B.6 Other (non-Gravity) GRACE Applications
Title: The Geodetic Reference Antenna in Space (GRASP) - A Mission to Enhance the Terrestrial Reference Frame
First Author: R. Steven Nerem
Presenter: R. Steven Nerem
Co-Authors: Yoaz Bar-Sever and the GRASP Team

Abstract: The Geodetic Reference Antenna in Space (GRASP) is a small satellite mission concept, currently being proposed to NASA's Earth Venture 2 (EV-2) announcement of opportunity, that is dedicated to the enhancement of all the space geodetic techniques, promising revolutionary improvements to the definition of the TRF, its densification, and accessibility. GRASP collocates GNSS, SLR, VLBI, and DORIS sensors on a supremely calibrated and modeled spacecraft, offering an innovative space-based approach to a heretofore intractable problem: establishing precise and stable ties between the key geodetic techniques used to define and disseminate the TRF. GRASP also offers a solution to another difficult problem, namely, the consistent calibration of the myriad antennas used to transmit and receive the ubiquitous signals of the present and future Global Navigation Satellite Systems (GNSS). We will describe how errors in the TRF impact our ability to answer key science questions, such as mean sea level rise, and present new analysis of GRASP's capability to improve various aspects of the TRF. We will also discuss opportunities for the geodetic community to contribute, support, and enhance this mission.

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Session: B.1 - Multidisciplinary Science
Title: Mass Transport and Climate Variability: Insights via GRACE
First Author: Jean Dickey
Presenter: Jean Dickey
Co-Authors: Olivier de Viron

Abstract: The GRACE satellite has been monitoring the change in the mass distribution at the Earth surface for nearly 10 years. This becomes enough to study long-term mass change, and to separate interannual variations from trends. This record permits us to analyze detailed mass variances of individual systems, such as the Greenland and Antarctic ice sheets or major continental aquifers. Moreover, the record facilitates the state of inter-relationships between regional gravity changes and the implied mass transport between different parts of the globe. However, care must be taken since these global indices are not orthogonal. We will consider regional mass variations that are highly correlated with global Indices (such as the Southern Oscillation Index) and their relation with teleconnection patterns.

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Session: B.1 - Multidisciplinary Science
Title: Inversion of Multiple Data Sets and GRACE's Contribution to Global Geodesy
First Author: Xiaoping Wu
Presenter: Xiaoping Wu
Co-Authors: X. Collilieux; Z. Altamimi; B.L.A. Vermeersen; R. Gross; I. Fukumori

Abstract: Using a global simultaneous inversion platform, multiple sets of geodetic data and geophysical information have been incorporated to estimate present-day surface mass variations and glacial isostatic adjustment (GIA) signatures and to assess their uncertainties quantitatively. With nearly global coverage and high precision, the GRACE mission contributes the most in this endeavor. However, to separate concurrent geophysical processes and parameters, data of different physical characteristics and reliable geophysical information from physical theory or prior knowledge are required to break the rank deficiencies and for improved consistency and accuracy. Currently, the global inversion is conducted following a kinematic methodology with very conservative and dynamically constructed a priori GIA information. Using GRACE gravity, geodetically measured relative surface velocities, and ocean bottom pressure models, separation of present-day surface mass trend (PDMT) and GIA signatures up to degree and order 60 has been achieved with very high accuracies in many global geodetic parameters such as geocenter velocity, time rate of change in J2, and other low-degree signatures. The reason for using relative velocities is to avoid a possible large drift rate in the realized International Terrestrial Reference Frame (ITRF) origin. Since the combination of data with relative velocities worked so well for the determination of geocenter velocity, it provides a quasi-independent way to validate the velocity component of the realized ITRF origin. More recently, we have conducted a new global inversion of GRACE, absolute ITRF2008 velocities, and ECCO/OMCT ocean bottom pressure models to solve for an ITRF2008 origin drift and a global solid Earth expansion rate, in addition to PDMT, GIA and plate motion parameters. The inversion shows that the origin of ITRF2008 is consistent with the long-term mean center-of-mass of the total Earth system with an accuracy better than 0.5 mm/yr, and the solid Earth is not currently expanding to within an uncertainty of 0.2 mm/yr. Still, many improvements are needed to further strengthen the results. In this presentation, we will also discuss issues of uncertain nature of ocean models for bottom pressure, data sparseness and discontinuity, uncertainties in GIA theories on rotational feedback and its effects, as well as future plans for our GRACE science team investigation.

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Session: B.1 - Multidisciplinary Science
Title: Water and temperature control of Vegetation productivity in Eurasia
First Author: Jinjun Tong
Presenter: Jinjun Tong
Co-Authors: I. Velicogna, J. Kimball

Abstract: We use GRACE measurements of time variable gravity, precipitation, evapotranspiration, and temperature from ERA-interim reanalysis, snow water equivalent (SWE) from AMSR-E, and NDVI and NPP from MODIS to analyze the response of vegetation to changing climate conditions in Eurasian during the period from August 2002 to August 2009. We show that the Yenisey and Lena river basin are warming and wetting, while the Ob river basin is warming and drying. We find that vegetation productivity in the Lena river basin is mainly limited by cold temperature constraints rather than moisture while in the Ob river basin vegetation productivity is mainly controlled by water limitation. We show how the time correlation between terrestrial water storage (TWS) and NPP changes in wet and dry areas and within different land cover types.

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Session: B.1 - Multidisciplinary Science
Title: Hydrological Behavior and Potential Land-Use Impacts in the Central Brazilian Savanna Biome: Preliminary Results from GRACE, TRMM, and MODIS
First Author: Laerte Ferreira
Presenter: Bettadpur Srinivas
Co-Authors: Bettadpur, S.; Coe, M.T.; Costa, M.H.

Abstract: The 2 million km2 Brazilian neotropical moist savanna biome (known as Cerrado), the headwater region of the major rivers of eastern South America, is the main agricultural frontier in the country, with nearly 50% of its original vegetative cover already converted, mostly to pasturelands [1]. As empirical data shows, the dominant pasture landscapes in the Araguaia-Tocantins basin, in the Cerrado - Amazon transition, has driven significant changes in regional runoff, river discharge and the atmosphere water transfer from soil reservoirs through vegetation [2-3]. In fact, in the prevalence of the current business-as-usual conversion scenario, feedbacks between land-cover change and climate are expected to significantly reduce precipitation and further impact surface hydrology [4]. In this study, data from GRACE, TRMM, and MODIS were used to assess the seasonal and interannual hydrological behavior of the three major Cerrado basins. Potential human-induced changes in the water cycle, at the sub-basin level, were also investigated. Specifically, water mass fluxes at the Tocantins-Araguaia, São Francisco and Paranaiba basins, for the 2004 - 2010 period, were evaluated based on monthly GRACE equivalent water thickness (cm) and TRMM precipitation (mm) data (http://trmm.gsfc.nasa.gov/). Gridded GRACE level-3 surface mass anomalies, destriped and smoothed [5], were obtained through the GRACE TELLUS (http://grace.jpl.nasa.gov). At the sub-basin level, 1km MODIS evapotranspiration data (monthly, 2010) [6], available from the Numerical Terradynamics Simulation Group (http://www.ntsg.umt.edu), were also evaluated. Over the three major basins, GRACE temporal signatures follow expected patterns, in agreement with the conspicuous Cerrado seasonality, with the Tocantins - Araguaia basin showing, on average, the largest ground / surface fluxes and amplitudes, what may be attributed, in part, to the key role played by the vast Araguaia flood plain in controlling and buffering the increase and depletion in water storage. At the sub-basin level, direct human-induced influence on the water cycle seems evident, as the proportion of evapotranspiration, relatively to the annual accumulated rainfall, decreases according to the % area converted in each basin.

1- Sano, E.E.; Rosa, R.; Brito, J.L.S.; Ferreira, L.G. Land cover mapping of the tropical savanna region in Brazil. Environmental Monitoring and Assessment, (doi 10.1007/s10661-009-0988-4), 2010.
2- Costa, M. H. et al. Effects of large-scale change in land cover on the discharge of the Tocantins River, Southeastern Amazonia. Journal of Hydrology, v. 283, 206-216, 2003.
3- Coe, M.T.; Latrubesse, M.E.; Ferreira, M.E.; Amsler, M.L. The Effects of Deforestation and Climate Variability on the Streamflow of the Araguaia River, Brazil. Biogeochemistry, 2011 (DOI 10.1007/s10533-011-9582-2).
4- Costa, M.H.; Pires, G.F. Effects of amazon and central Brazil deforestation scenarios on the duration of the dry season in the arc of deforestation. International Journal of Climatology,www.interscience.wiley.com, 2009.
5- Swenson, S. C.; J. Wahr. Post-processing removal of correlated errors in GRACE data, Geophys. Res. Lett., 33, L08402 (doi:10.1029/2005GL025285), 2006.
6- Mu, Q., Zhao, M.; Running, S. W. Improvements to a MODIS Global Terrestrial Evapotranspiration Algorithm. Remote Sensing of Environment, Volume 115, 1781-1800 (doi:10.1016/j.rse.2011.02.019), 2011.

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