The preliminary model was created with 111 days of selected Grace data to help calibrate and validate the mission’s instruments and improves knowledge of the gravity field so much it is being released to oceanographers now, months in advance of the scheduled start of routine Grace science operations, scientists say. Grace senses minute variations in gravitational pull from local changes in Earth’s mass by precisely measuring, to a tenth of the width of a human hair, changes in the separation of two identical spacecraft following the same orbit some 220 kilometers (137 miles) apart. It will map the variations from month to month, following changes imposed by the seasons, weather patterns and short term climate change.
Grace is the newest tool for scientists working to unlock secrets of ocean circulation and its effects on climate and is providing a more precise definition of Earth’s geoid, an imaginary surface defined only by Earth’s gravity field, upon which the planet’s ocean surfaces would lie if not disturbed by other forces such as ocean currents, winds and tides.
The geoid height varies around the world by up to 200 meters (650 feet). Grace will allow scientists to know the exact geoid height with centimeter-like precision, which will allow scientists to separate out gravitational effects on the ocean’s surface and improve the accuracy of satellite tools that measure sea surface height as well as ocean heat storage and global ocean circulation.
If you’ve read this far, you deserve a little SciScoop-style comic relief, so here it is, a somewhat humorous aside about why understanding global ocean circulation is so important. The second line of the hymn started in the title of this article is, of course, “To track a rubber duckie like me…”