Geoid earth

GOCE satellite with ion propulsion system. (Credits: ESA /AOES Medialab). Click to enlarge.

On March 17, 2009, the European Space Agency (“ESA”) launched a satellite called The Gravity Field and Steady-State Ocean Circulation Explorer (“GOCE”), which carried a gradiometer, allowing it to detect very fine density differences on the Earth’s surface. The satellite is designed to fly much lower than other satellites (it orbits at an altitude of 260 km or 161 miles) and uses an ion propulsion trajectory to keep the machine steady despite atmospheric drag. The 5-meter long satellite is designed as one piece with no moving parts. (The atmosphere becomes more rarified farther from earth, and so an orbit at a lower altitude experiences more drag and more turbulence.)

In a press release issued today, the ESA said that twelve months’ worth of data collection by GOCE concerning the Earth’s gravity has allowed it to model the gravitational fields of the planet. The geoid model shows the idealized surface of the planet covered in ocean without tides or currents and only affected by gravity.  ESA says that a

“precise model of Earth’s geoid is crucial for deriving accurate measurements of ocean circulation, sea-level change and terrestrial ice dynamics. The geoid is also used as a reference surface from which to map the topographical features on the planet. In addition, a better understanding of variations in the gravity field will lead to a deeper understanding of Earth’s interior, such as the physics and dynamics associated with volcanic activity and earthquakes.”

Geoid model from GOCE data. (Credits: ESA/HPF/DLR.) Click to enlarge.

The model is oddly egg-shaped with pertuberances over the northern European region and the South Pacfic over Australia. The ESA press release (linked above) contains an animation of the model which shows the distortions more clearly.

A thorough explanation of the data is contained in the second GOCE newsletter issued two days ago. Being Europeans the authors were free to entitle the first article “Mission Accomplished!” an expression our last President caused to be expunged from American public discourse. The publication explains how to access the data from the mission and provides a software toolbox (to be demonstrated today) that will allow you to do such things as “Compute gravity anomalies, height anomalies and vertical deflections on the surface of the terrain for a range of maximum degree and order expansions over a grid or transect.”

The GOCE portal is regularly updated and contains the toolbox, data access links and instructions.

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