Atmospheric pressure loading displacement of SLR stations

Abstract

This paper addresses the local displacement at ground stations of the world-wide Satellite Laser Ranging (SLR) network induced by atmospheric pressure variations. Since currently available modelling options do not satisfy the requirements for the target application (real-time availability, complete coverage of SLR network), a new representation is developed. In a first step, the 3-dimensional displacements are computed from a 6-hourly grid of 1°×1° global pressure data obtained from the ECMWF, for the period 1997–2002. After having been converted into pressure anomalies, this pressure grid is propagated into horizontal and vertical station displacements using Green’s functions and integrating contributions covering the entire globe; oceans are assumed to follow the inverted barometer (IB) approximation. In the next step, a linear regression model is developed for each station that approximates the time-series of the predicted vertical displacements as well as possible; this regression model relates the vertical displacement of a particular station to the local (and instantaneous) pressure anomaly. It is shown that such a simple model may represent the actual vertical displacements with an accuracy of better than 1 mm; horizontal displacements are shown to be negligible. Finally, the regression model is tested on actual SLR data on the satellites LAGEOS-1 and LAGEOS-2, covering the period January 2002 until April 2003 (inclusive). Also, two model elements are shown to be potential risk factors: the global pressure field representation (for the convolution method) and the local reference pressure (for the regression method). The inclusion of the atmospheric pressure displacement model gives improvements on most of the elements of the computations, although the effects are smaller than expected since the nominal effect is absorbed by solved-for satellite parameters.