GRACE “Gravity Recovery and Climate Experiment” Use in measuring Earth’s gravitational field and geoids By Jacob Launder

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

What “GRACE” is… 2 satellites orbiting Earth 2 satellites orbiting Earth Use K-band microwaves to measure distance changes. Use K-band microwaves to measure distance changes. Use GPS and Accelerometers as well. Use GPS and Accelerometers as well.

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

How it works… One satellite 220km ahead. One satellite 220km ahead. Changes in a micrometer Changes in a micrometer Movements cause by strengths in gravity Movements cause by strengths in gravity

World Map

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

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

SSH from GRACE and Jason-1 Important for climate because it shows heat content and the amount in upper layer. Important for climate because it shows heat content and the amount in upper layer. Heat can then return to atmosphere. Heat can then return to atmosphere.

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

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