A new fiber optic gradiometer for 4-D absolute differential gravity

We introduce the concept of absolute differential gravimetry using fiber op tic-based laser interferometry. Absolute differential gravimetry provides a n instantaneous determination of the difference in gravity between two or m ore points on or beneath the surface of the earth. Applications include enh ancing the resolution of the gravity field, as well as subsurface fluid and structure monitoring. With a network of sensors, observation of time depen dent variations of the gravity field is also possible. Results from a proof -of-concept prototype instrument using fiber-optic coupler technology repre sent the first time absolute laser interferometric differential gravity dat a have been collected. Implications of the new measurement method in terms of geophysical studies and future research plans are discussed.