Airborne gradiometry error analysis

Gravity gradiometry is one of the older methods of determining the Earth's local gravitational field, but lies in the shadow of more conventional static and moving-base gravimeter-based systems. While the static torsion balance appears to have been relegated to the museum, support for the airborne and space-borne differential accelerometer (gradiometer) continues so as to overcome limitations in spatial resolution and accuracy inherent in ordinary moving-base gravimetry. One airborne system exists, building on 30 year old technology concepts, and new technologies ( e. g., cold-atom interferometry) promise significant improvements. Concomitant advances are required to measure accurately the angular velocity and angular acceleration of the platform, which inseparably combine ( in an absolute sense) with the Earth's gravitational gradients. A numerical analysis of instrument errors, with simulated aircraft dynamics, shows that navigation-grade gyros are just sufficient to account for these effects in gradiometers with 1E/root Hz sensitivity. More accurate instruments, with 0.1 E/root Hz sensitivity, require commensurate sensitivity in the gyros, of the order of 0.01 degrees/h/root Hz = 1.5 x 10(-4)degrees/root h for typical survey aircraft dynamics. On the other hand, typical orientation errors in the platform, which are problematic for vector gravimetry, are much less of a concern in gradiometry. They couple to the gradient signals and affect only the very low frequencies of the total gradient error.