Determination of vertical displacements over the coastal area of Korea due to the ocean tide loading using GPS observations

This paper describes the GPS applicability for detecting the vertical displacements of ground stations caused by ocean tide loading effects. An experiment was carried out using 12 permanent GPS stations located in the coastal area of Korea using data in the period 1 July until 26 August 2003. The relative height differences were calculated from hourly DGPS data processing based on the carrier-phase observation. The power spectra of the M-2 and N-2 constituents of ocean tide loading were derived using the CLEAN algorithm. The differential vertical displacements generated by the ocean tide loading effect are typically 3-25 mm in coastal area of the Korea. We compared the results from GPS with those of the ocean tide models, NAO.99Jb regional model and GOT00.2, FES99 global models. The M-2 (N-2) amplitude differences of vertical displacements between GPS and GOT00.2 is 1.22 +/- 3.61 mm (1.01 +/- 1.48 mm), and that of the M-2 (N-2) amplitude difference between GPS and FES99 is 0.04 +/- 4.64 mm (0.64 +/- 1.75 mm), whereas the M-2 (N-2) amplitude difference between GPS and NAO.99Jb are 0.05 +/- 1.03 mm (0.86 +/- 1.18 mm). The highest vertical displacements at the PALM station are found for 24.5 +/- 0.7 mm from GPS observation, and 22.9 mm from the regional model NAO.99Jb and 13.17 and 10.00 mm from the global models GOT00.2 and FES99, respectively. These values show that the vertical displacements derived from GPS are in good agreement with those of the regional model NAO.99Jb around Korea, more than with the global models. This result indicated that GPS is an effective tool to measure the vertical displacement caused by the ocean tide loading effect in the coastal area, and we need to use the NAO.99Jb ocean tide model rather than the global ocean tide models in and around the Korean peninsula for position determination with permanent GPS installations. This work demonstrates that vertical displacement caused by the M-2 and N-2 constituents of ocean tide loading can be measured by carrier-phase DGPS. (c) 2006 Elsevier Ltd. All rights reserved.