Detecting andmitigating ocean tidal loading displacements in the Bay of Fundy using GPS

Tidal induced displacement is one of the systematic errors that contribute to the scatter in the geodetic measurements derived from the GPS system. This paper focuses on ascertaining and reducing tidal induced errors due to ocean tide loading (OTL) at two GPS sites, namely CGSJ (Coast Guard Saint John, New Brunswick) and DRHS (Digby High School, Nova Scotia), established under the Princess of Acadia project in Saint John, New Brunswick and in Digby, Nova Scotia, respectively. Baseline solutions were obtained by processing 3 and 24 hourly GPS data for the period of onemonth, using differential positioning software DIPOP and its client end GUI, FACE v2.0. The observed differential variations of GPS sites were compared to the OTL modeled differential variations along the baselines for statistical analysis. The predictive differential ocean tide loading induced variations of the baselines were modeled with global ocean tide model FES 95.2 (0.5 by 0.5 resolution) supplemented with a higher resolution regional tide model by Pagiatakis (0.25 by 0.25 resolution). After modeling for tidal effects the solutions for both the height component and baseline length show daily repeatability better than 1.5 mm for baselines ranging from 87.5 km to 170 km. The tidal model used in the investigation explains the observed motion considerably well, with correlation coefficients of greater than 0.70 between modeled and observed curves. Elimination of tidal effects has resulted in day-to-day rms reduction of height better than 80 percent.