Improving Pressure Loading Modeling at VLBI Sites

We examine the atmospheric pressure loading deformations at VLBI (very long baseline interferometry) sites due to temporal variations of atmospheric mass and the contribution from pressure at the ocean floor. Typical peak-to-peak pressure loading displacements at VLBI stations are 10-20 mm in the vertical and 2-4 mm in the horizontal. The temporal variations have seasonal as well as interannual variations.

Our initial pressure loading series was computed assuming the inverted barometer hypothesis. The next step was to investigate the non-inverted barometer contribution from ocean areas. Atmosphere and Ocean De-aliasing Level-1B (AOD1B) products are used to estimate the ocean-area contribution in the pressure loading calculation. We used the surface atmospheric pressure from the ECMWF ERA Interim model and the ocean bottom pressure from AOD1B. To define the land-ocean boundary, we use a land-sea mask with at least the resolution of the ECMWF data itself. The calculations of the horizontal and vertical displacements due to loading are performed using the Green's Function method originally presented by Farrell (1972).

The resulting loading series are evaluated by applying them in the analysis of VLBI data to determine if analysis results improve. Specifically, we investigate the reduction in baseline length scatter and site position vertical and horizontal scatter when different loading series are applied in VLBI solutions for 1) the 2-week CONT14 and CONT17 R&D campaigns of continuous observing and 2) VLBI sessions since 2000. We compare the generated loading series with the GSFC operational series based on the NCEP Reanalysis model as well as with other pressure loading series, for example, the EOST loading series (Univ. of Strasbourg, France).