CONTINUOUS GRAVITY OBSERVATIONS USING JOINT INSTITUTE FOR LABORATORY ASTROPHYSICS ABSOLUTE GRAVIMETERS

We discuss two different 1-month gravity records taken with two different Joint Institute for Laboratory Astrophysics (JILA) gravimeters. These records were corrected for the effects of Earth tides, ocean loading, local and global barometric effects, and polar motion. These data allowed precise determinations of the local air pressure admittance. We also obtained a value for the second-order gravimetric factor which agreed with the theoretical value to about 0.3% where the predominant uncertainty is the ocean load modeling. The corrected noise spectra were white above 1 cycle/d with a spectral noise density of about 80-mu-Gal/square-root Hz. We note that absolute gravimeters have a sensitivity to time varying gravity that is comparable to that obtained with superconducting relative gravimeters. The sensitivity of these data emphasizes the need for better modeling of ocean loads, air pressure effects, and even man-made environmental noise.