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Residual K1 and K2 oscillations in precise GPS solutions: case study

Bogusz J., Figurski M.

Artificial Satellites : Journal of Planetary Geodesy

2011

Vol. 46, No. 2

75--91

The continuous GPS observations from Polish Ground-Based Augmentation System (ASG-EUPOS) with two different strategies were analysed. Within the first one the adopted 3-hour observation window was shifted every hour to obtain hourly geocentric coordinates for investigation of the short-period oscillations. The second was the daily solution using EPN (EUREF Permanent Network) standards and recommended models. The Eterna 3.4 software was used for determination of the variations in the tidal frequencies. The almost three-year course of data allow for investigation even close tidal frequencies, especially in PSK1 and S2K2 groups. The variations of the Up component in K1 and K2 waves were found to be significant. It turned out that K1 frequency involves the greatest amount of energy reaching even 11 mm for the Up component. Spurious oscillation up to 4 mm and the period of about 1 year in GPS height time series at the selected ASG-EUPOS sites were obtained. Long-period GPS satellite orbit modelling errors could be directly responsible for small periodic biases in station position determinations as well as the repeating geometry of the satellite constellation with respect to the tracking stations. But it is very difficult to distinguish whether it comes from artefacts (transition of K1 ad K2 in long periods) or real effects (local hydrology). Comparison with the geophysical fluid loadings needs further investigations.

Analysis of long-term variations in physico-chemical parameters of seawater in the southern Baltic Sea; an approach to incomplete data series

Łysiak-Pastuszak E., Cyberski J.

Oceanologia

1999

No. 41 (4)

553-572

Long-term trends in the variations of physical and chemical parameters characterising seawater were analysed by a method, originally used in climatology, allowing detection of optimal cycles of these variations in incomplete (intermittent) data time series. The method was used to analyse measurements of water temperature, salinity, density, oxygen saturation and nutrient concentrations (phosphate, nitrate and silicate) from station BMP L1 (P1) in the Gdansk Deep region obtained between 1979 and 1996. All parameters revealed a pattern of regular cycles, the spectrum of the cycles being dependent on the parameters and water layer. As regards reconstruction and forecasting in the deterministic-stochastic model, statistically significant correlation coefficients in the 0.57-0.97 range were obtained between the calculated and empirical data for all the parameters examined. The correlation was poorest in the case of silicate. Linear regression trends calculated in the deterministic-stochastic model were in relatively good agreement with those obtained using Hirsch's non-parametric test.