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GRACE:
Gravity Recovery And Climate Experiment
An Earth System Science Pathfinder (ESSP) Mission

Byron D. Tapley
(Principal Investigator)
Center for Space Research
The University of Texas at Austin

Chris Reigber
(Co-Principal Investigator)
GeoForschungsZentrum
Potsdam

GRACE HPC Poster



GRACE Mission

Flight Configuration for GRACE Science Goals
High resolution, mean & time variable gravity field mapping for Earth System Science applications

Mission Systems
Instruments

  • HAIRS (JPL/SSL/APL)
  • SuperSTAR (ONERA)
  • Star Cameras (DTU)
  • GPS Receiver (JPL)
Satellite (JPL/DSS)
Launcher (DLR/Eurokot)
Operations (DLR/GSOC)
Science (CSR/JPL/GFZ)

Orbit
Launch: February 2002
Altitude: 485 km
Inclination: 89 deg
Eccentricity: ~0.001
Lifetime: 5 years
Non-Repeat Ground Track, Earth Pointed, 3-Axis Stable

COMPUTATIONAL CHALLENGE

Up to 180x180 spherical harmonics (~32,400 parameters) n

  • 180x180 solution may be required to accurately smooth to 160x160
Daily computational task
  • Numerical integration of ~194,000 dif. eq (6n)
  • Process ~17,280 SST observations (m)
  • Calculate and write 4.5 Gbytes of partial derivatives
  • Accumulate partials (m*n*n ~18 trillion FLOPs)
  • Comparable requirements for GPS data
Requires > 8 Gbytes of machine memory for accumulation, solution, and covariance (n*n)
  • Solution covariance alone will be 4.2 Gbytes (n*n/2)

COMPUTATIONAL REQUIREMENTS

HPC Resources Used

  • TACC T3Es, NASA T3E and ORIGIN 2000, CSR/TACC Cray SV-1
  • TACC SGI/STK Data Archive
Computational rate (for 180x180 solution)
  • Each day's processing requires 30-60 CPU hours (@200 Mflops)
  • Must be able to process several days worth of data each day
Storage requirements (for 180x180 solution)
  • ~8 Gbytes or partials each day (shprt term storage)
  • 400-800 Gbytes of information equations and covariances each year
If computational load shared between CSR and remote computers, ~8 Gbytes/day must move across internet

On order of 100,000 CPU hours per year

COMPUTATION STRATEGIES

Generate daily data equations concurrently on current vector platform (essentially parallel/vector)

  • Edit data & integrate satellite trajectories
  • Calculate and write partials (~8 Gbytes/day)
Accumulate and solve information equations on available parallel platforms
  • Already demonstrated to be highly parallel process
  • Using computing resources elsewhere requires moving hunmdreds of Gbytes of data across internet

GRACE Processing Flow


GRACE: Mission Concept

DEMONSTRATED PERFORMANCE

Working with PLAPACK developers to enhance parallel performance

Using 32 T3E nodes, calculate soultion and covariance for 110x110

  • 334 Mflops/node (50% peak), 11 Gflops total, 7 min wallcloack
Using 512 T3E nodes, calculate solution and covariance for 200x200
  • 183 Mflops/node (30% peak), 94 Gflops effective total speed
Using a single SV-1 MultiStreaming Processor, nearly 1 Gflop attained for 120x120 data accumulation (MSP has 4.8 Gflop theoretical peak)
  • Actual performance significantly affected by overall load on machine due to memory bandwidth limitations
Go to the UTopia web site
Go to University of Texas web site

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The GRACE mission is jointly implemented by NASA and DLR under
the NASA Earth System Science Pathfinder Program.

Last Modified: Thu Feb 12, 2004
CSR/TSGC Team Web