Earth's Gravitational Shape In Detail

RobHart writes "The European Space Agency (ESA) has released detailed information about the Earth's gravitational shape, based on data from the ESA's GOCE satellite (Gravity Field and Steady-State Ocean Circulation Explorer). The link includes an interesting animation of the data, using an appropriately distorted Earth."

Re:Didn't it use to be highly classified data?

[tibit]

I think that a lot of U.S. nuke missile arsenal predateds GPS -- maybe they upgraded avionics to take advantage of it, I don't know. If there was to be any sort of a nuclear showdown, then the GPS would either go down or the clear data would be turned off, only encrypted one remaining. I think that if you're after long range weapons, you really need INS, and for that accurate geoid is a must. I would presume that any sort of a ballistic or cruise missle guidance system would have targeting accuracy specified without GPS augmentation (inertial only), with augmentation providing a "free" improvement if available.

Apart from GPS and GLONASS, there is no "other" sat-based navigation available yet. Getting any sort of a satnav receiver through its paces of military QA, you can't really add support for other systems on a whim. I think that all satnav receivers installed in U.S. weapons support GPS, and won't support anything else in the next decade or two.

You don't use the geoid to plan any sort of a trajectory. You use it for inertial navigation -- for converting outputs of your inertial reference sensors (gyros and accelerometers) into a position fix. To do this accurately, you need accurate, low-drift and low-noise sensors. Once your sensors get good enough, improving their accuracy doesn't improve the accuracy of your fix! To get any further improvement, you need to improve the accuracy and resolution of your geoid data. By my back-of-the-envelope calculations, GOCE's geoid is supposedly (based on published details) good enough to match the best inertial reference sensors out there, and would allow you to obtain the best inertial fix that's possible with current technology.