Frequency-dependent atmospheric pressure admittance of superconducting gravimeter records using least squares response method

Atmospheric pressure is one of the largest environmental noise sources in surface gravity observations. This effect is usually removed by two different methods that are based on the availability of pressure data and their temporal and spatial distribution. The first method is based on a physical approach by either convolving the global surface (2D) pressure field with an appropriate Green's function or by using a 3D spherical model for attraction determination. The second method determines a transfer function between atmospheric pressure and gravity, known as barometric pressure admittance. In this paper, we focus on the second method by adopting an alternative approach for the determination of the pressure admittance that is based on the least-squares (LS) product spectrum of the atmospheric pressure and gravity time series. It represents a smooth gravity response to air pressure fluctuations in specific frequency bands (frequency-dependent admittance) with a magnitude of about 0.293 mu Gal/mbar in the low-frequency band and 0.443 mu Gal/mbar in the high-frequency band. This transfer function is derived from a 1-year data set recorded at the Canadian Superconducting Gravimeter Installation (CSGI; Cantley, Canada). The results show that the frequency-dependent pressure admittance reduces the quadratic norm of the gravity residuals by 95.4% while the physical approach correction which is based on the global atmospheric data reduces it by 92.2%. In addition, the frequency-dependent admittance shows an obvious improvement in the coherence spectrum. (C) 2008 Elsevier B.V. All rights reserved.