Gravity Surveys Using a Mobile Atom Interferometer

Measuring gravity is important in geodesy for e.g. hydrological monitoring and mineral exploration. Though atomic gravimeters have become the most sensitive way to measure absolute gravity in well-controlled conditions, the performance of field-operation atomic gravimeters is constrained due to their relatively complex and fragile apparatus. We demonstrate field-operation of a mobile atomic gravimeter for time-variable gravity measurements and gravity surveys. In the laboratory, tidal gravity variation is measured with a sensitivity of 37 n$g$/$\surd $Hz and a long-term stability of better than 2 n$g$, revealing the gravitational ocean loading effect on the local tide in the San Francisco Bay. In gravity surveys on the Berkeley hills, absolute gravity is measured with a sensitivity of \textasciitilde 500 n$g$/$\surd $Hz and precision of \textasciitilde 60 n$g$, obtaining the density of the subsurface rocks from the vertical gravity gradient. This work paves the way for bringing field-operation atomic gravimeters to geodesy.