GRACEGRACE“Gravity Recovery and Climate “Gravity Recovery and Climate

Experiment”Experiment”

Use in measuring Earth’s Use in measuring Earth’s gravitational field and geoidsgravitational field and geoids

By By Jacob LaunderJacob Launder

Earth and TOPEX/PoseidonEarth and TOPEX/Poseidon

Earth does not Earth does not have same gravity have same gravity everywhere.everywhere.

TOPEX measures TOPEX measures SSH.SSH.

Changes can be Changes can be from a range of from a range of things though.things though.

What “GRACE” is…What “GRACE” is…

2 satellites orbiting 2 satellites orbiting EarthEarth

Use K-band Use K-band microwaves to microwaves to measure distance measure distance changes.changes.

Use GPS and Use GPS and Accelerometers as Accelerometers as well.well.

InstrumentsInstruments

KBR- Ranging instrumentKBR- Ranging instrument Accelerometer (ACC) – ONERA Accelerometer (ACC) – ONERA

Superstar AccelerometerSuperstar Accelerometer Star Camera Assemblies (SCA) – For Star Camera Assemblies (SCA) – For

attitude dataattitude data Laser Corner-Cube Reflector Laser Corner-Cube Reflector

Assembly (LRA)- orbit verificationAssembly (LRA)- orbit verification

How it works…How it works…

One satellite One satellite 220km ahead.220km ahead.

Changes in a Changes in a micrometermicrometer

Movements cause Movements cause by strengths in by strengths in gravitygravity

World MapWorld Map

How this Helps…How this Helps…

Before these measurements could Before these measurements could only be done by ground based only be done by ground based measurementsmeasurements

All satellite depictions would be All satellite depictions would be much more vague.much more vague.

Now the gravitational anomaly can Now the gravitational anomaly can be seen on a worldwide scale using be seen on a worldwide scale using satellites.satellites.

TOPEX + GRACETOPEX + GRACE

Used for causes in SSH.Used for causes in SSH. GRACE can find geoid, while TOPEX GRACE can find geoid, while TOPEX

can measure SSHcan measure SSH The data together will be able to see The data together will be able to see

what causes the SSH to vary from what causes the SSH to vary from the form of the geoid. the form of the geoid.

Temp. or currentsTemp. or currents

SSH from GRACE and Jason-1SSH from GRACE and Jason-1

Important for climate because it shows heat Important for climate because it shows heat content and the amount in upper layer.content and the amount in upper layer.

Heat can then return to atmosphere.Heat can then return to atmosphere.

Dynamic TopographyDynamic Topography

DT: missing piece because oceans are not DT: missing piece because oceans are not stationary.stationary.

Because of winds and ocean movement.Because of winds and ocean movement. The ultimate goal with GRACEThe ultimate goal with GRACE Need SSH and GeoidNeed SSH and Geoid Only 1% of total topography variationOnly 1% of total topography variation But very important for current speed and But very important for current speed and

directiondirection

ConclusionConclusion

GRACE- twin satellites measuring GRACE- twin satellites measuring geoidgeoid

This couples with TOPEX/Poseidon This couples with TOPEX/Poseidon data will give Dynamic Topographydata will give Dynamic Topography

Used to help understand changes in Used to help understand changes in SSHSSH

Hopes are to strengthen models and Hopes are to strengthen models and understand the oceans role in understand the oceans role in regulation Earth’s climate.regulation Earth’s climate.