Topography-Assisted downward Continuation of Airborne Gravity: An Application for Geoid Determination in Taiwan

  • Author(s): Yu-Shen Hsiao and Cheinway Hwang
  • DOI: 10.3319/TAO.2009.07.09.01(T)
  • Keywords: Geoid, Downward continuation, Gravity anomaly, Least-squares collocation, Topography
  • Citation: Hsiao, Y. S. and C. Hwang, 2010: Topography-assisted downward continuation of airborne gravity: An application for geoid determination in Taiwan. Terr. Atmos. Ocean. Sci., 21, 627-637, doi: 10.3319/TAO.2009.07.09.01(T)

We investigated the Fourier transform-based downward continuation (DWC) of airborne gravity anomalies around Taiwan assisted by topographic information. The topographic data are from the latest collections of elevations and ocean depths. The DWC employs a remove-compute-restore (RCR) procedure in which the topography is removed prior to computation and then restored to achieve stable solutions. The topographic gravity effect is evaluated point-wise using the Gaussian quadrature. A Gaussian filter with an optimal smoothing parameter reduces the noise-amplifying effect of DWC. Use of topography in DWC leads to improvements of 3 to 6 mgal of gravity on land. Surface and downward continued gravity anomalies are used to determine geoidal heights by least squares collocation (LSC) in a similar RCR procedure through the same topographic data. The accuracy of the geoidal heights at Taiwan¡¦s first-order leveling benchmarks is improved by 1 to 2 cm due to inclusion of downward continued airborne gravity.

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