GPS Unaffected By Tsunami (Earthquake)

It’s sort of neat to be in on the ground floor of an urban legend but the truth, the whole truth, must be told about effects (or lack thereof) of the Asian tsunami on flight navigation. Simply put, there are none. Not long after the devastating undersea earthquake (widely reported at 8.9 on the Richter scale, it was the largest in decades, worldwide) and resulting waves, scientists began speculating on the effect of the event on the Earth’s cosmic behavior. According to Dr. Richard Gross, at the Jet Propulsion Laboratory, the quake did cause the earth’s rotation to speed up by about three microseconds and caused a slight wobble. But he said the changes are too minuscule to worry about. That didn’t stop some from speculating on the effect such changes might have on GPS accuracy. FAA spokesman William Shumann told AVweb that GPS satellites don’t rely on a reference to day length to do their job. “They are very precise clocks that continuously transmit a timing mark and the satellite’s location in the earth-centered, earth fixed-coordinate system,” Shumann wrote in an e-mail. “Periodic maintenance maneuvers on the satellites keep them in their desired orbits and that prevents any undesired precessing of the GPS constellation with respect to the earth’s rotation.” Besides, there’s nothing absolutely precise about our observation of the earth’s rotation. Every so often scientists have to add or subtract a “leap second” to compensate for variations in day length.