A comparison of predicted and observed ocean tidal loading displacements around the Puget Sound

Author

Tanessa Caitlyn Morris, University of Montana, MissoulaFollow

Graduation Year

2022

Graduation Month

May

Document Type

Thesis

Degree Name

Bachelor of Science

School or Department

Geosciences

Major

Geosciences

Faculty Mentor Department

Geosciences

Faculty Mentor

Dr. Hilary Martens

Keywords

geophysics, ocean tides, GPS, Earth, geoscience

Subject Categories

Geophysics and Seismology

Abstract

Around coastlines and in shallow oceans, models of ocean tidal loading (OTL) are not highly accurate and can create sources of error in OTL analysis. OTL is tides moving ocean water that cause the surface of Earth to deform. In this study, forward-modelled predictions of OTL are compared to observations from Global Navigation Satellite System (GNSS) data to explore the elastic deformation response of Earth to OTL around the Puget Sound. Data from 75 stations were processed to yield position estimates at intervals of 5 minutes for a year. The OTL model used for comparison was the FES2014b ocean-tide model loading a spherically symmetric, non-rotating, elastic, and isotropic (SNREI) Earth model. The three tidal frequency bands used were the semidiurnal (M₂), diurnal (O₁), and fortnightly (M_f). The M₂ tide is the largest and M_f the smallest. The model and observations have the largest residual displacements of 5 mm for the M₂ tide, and the smallest 2 mm for the O₁ tide. The particle motion residuals have strong spatial coherence in the M₂ and O₁ tide but are less coherent with the M_f tide. These residuals indicate that either the models of OTL and/or the observations of OTL have deficiencies. Model deficiencies are likely due, in part, to the FES2014b model not extending fully into and accounting for the complex morphology of the Puget Sound. Another element explored was quantifying the difference in observed OTL when a sidereal filter is applied to the GNSS time series. A sidereal filter is used to remove multipath errors that occur every sidereal day when GNSS satellite orbits repeat. The largest residual displacements were 1 mm in the M_f tidal band and the smallest 0.5 mm in the M₂ band. These differences can alter the observations used in OTL analysis, which impacts model comparisons. Multipath errors can overlap in frequency space with tidal frequencies, so the use of a sidereal filter must be carefully considered before its application.

Honors College Research Project

No

GLI Capstone Project

no

Recommended Citation

Morris, Tanessa Caitlyn, "A comparison of predicted and observed ocean tidal loading displacements around the Puget Sound" (2022). Undergraduate Theses, Professional Papers, and Capstone Artifacts. 375.
https://scholarworks.umt.edu/utpp/375