Analysis of superconducting gravimeter data from Table Mountain, Colorado

We present an analysis of more than two years of data from the superconducting gravimeter CO24 at the National Oceanic and Atmospheric Administration's Table Mountain Geodetic Observatory (TMGO) near Boulder, Colorado. The gravity data, sampled at intervals of 5 s, were cleaned for gaps, disturbances and offsets and then decimated to 1 hr, and an ETERNA analysis was done to determine the tidal gravimetric factors and phases, during which the atmospheric pressure loading and the period and damping of the free core nutation were obtained. We find T=418 ± 14 days and 1152<Q<2848. A short‐period analysis of the five quietest days in the seismic‐mode band (200–600 s) shows the combined instrument/site noise to be one of the lowest of all the superconducting gravimeters analysed to date. For the long periods, a local tide, including various ocean loading models, is subtracted from the data and the residual gravity shows very good correlation with IERS polar motion. Instrument drift is well fitted by a positive exponential function with a value of about 5 μ gal yr− 1 at the end of the record. Analysis of the pressure using a complex frequency‐dependent admittance shows some improvement in noise over using a simple scalar admittance function. In the Slichter mode and core mode bands, there are no significant peaks to be noted; more definitive evidence of signals from the Earth's core will require stacking using the Global Geodynamics Project network. TMGO is an extremely stable site with excellent noise characteristics.