Establishing requirements for gravity surveys for very accurate inertial navigation

The accuracy of broad-area gravity survey methods is evaluated, with a focus on the applicability of the measurements to unaided inertial navigation systems (INSs) for ships and aircraft. The methods considered are satellite altimetry, aircraft gravimetry, aircraft gradiometry, satellite-to-satellite tracking, and satellite gradiometry. A universal formula for the power-spectral density of gravity-disturbance residuals after survey is derived and multiplied with the INS transfer function, and time histories of the rms navigation errors are obtained by integrating over all frequencies. All of the systems are shown to reduce INS error, but satellite-to-satellite tracking and satellite gradiometry are much less effective than the other methods. For an aircraft at 500 kts, the rms position errors after 10 h are found to be less than 170 ft for satellite altimetry, 60 ft for aircraft gradiometry, and 30 ft for aircraft gravimetry.