GRACE Gravity Recovery and Climate Experiment

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GRACEGravity Recovery and Climate Experiment

• Use in measuring Earths gravitational field and
  geoids
• By
• Jacob Launder

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Earth and TOPEX/Poseidon

• Earth does not have same gravity everywhere.
• TOPEX measures SSH.
• Changes can be from a range of things though.

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What GRACE is

• 2 satellites orbiting Earth
• Use K-band microwaves to measure distance
  changes.
• Use GPS and Accelerometers as well.

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Instruments

• KBR- Ranging instrument
• Accelerometer (ACC) ONERA Superstar
  Accelerometer
• Star Camera Assemblies (SCA) For attitude data
• Laser Corner-Cube Reflector Assembly (LRA)- orbit
  verification

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How it works

• One satellite 220km ahead.
• Changes in a micrometer
• Movements cause by strengths in gravity

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World Map
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How this Helps

• Before these measurements could only be done by
  ground based measurements
• All satellite depictions would be much more
  vague.
• Now the gravitational anomaly can be seen on a
  worldwide scale using satellites.

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TOPEX GRACE

• Used for causes in SSH.
• GRACE can find geoid, while TOPEX can measure SSH
• The data together will be able to see what
  causes the SSH to vary from the form of the
  geoid.
• Temp. or currents

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SSH from GRACE and Jason-1

• Important for climate because it shows heat
  content and the amount in upper layer.
• Heat can then return to atmosphere.

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Dynamic Topography

• DT missing piece because oceans are not
  stationary.
• Because of winds and ocean movement.
• The ultimate goal with GRACE
• Need SSH and Geoid
• Only 1 of total topography variation
• But very important for current speed and
  direction

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Conclusion

• GRACE- twin satellites measuring geoid
• This couples with TOPEX/Poseidon data will give
  Dynamic Topography
• Used to help understand changes in SSH
• Hopes are to strengthen models and understand the
  oceans role in regulation Earths climate.