Abstract. The 100th anniversary of the Liverpool Tidal Institute (LTI) was
celebrated during 2019. One aspect of tidal science for which the LTI
acquired a worldwide reputation was the development and use of tide
prediction machines (TPMs). The TPM was invented in the late 19th
century, but most of them were made in the first half of the 20th
century, up until the time that the advent of digital computers consigned
them to museums. This paper describes the basic principles of a TPM, reviews
how many were constructed around the world and discusses the method devised
by Arthur Doodson at the LTI for the determination of harmonic tidal
constants from tide gauge data. These constants were required in order to
set up the TPMs for predicting the heights and times of the tides. Although
only 3 of the 30-odd TPMs constructed were employed in operational tidal
prediction at the LTI, Doodson was responsible for the design and oversight
of the manufacture of several others. The paper demonstrates how the UK, and
the LTI and Doodson in particular, played a central role in this area of
tidal science.
AbstractA standard geodetic GPS receiver and a conventional Aquatrak tide gauge, collocated at Friday Harbor, Washington, are used to assess the quality of 10 years of water levels estimated from GPS sea surface reflections. The GPS results are improved by accounting for (tidal) motion of the reflecting sea surface and for signal propagation delay by the troposphere. The RMS error of individual GPS water level estimates is about 12 cm. Lower water levels are measured slightly more accurately than higher water levels. Forming daily mean sea levels reduces the RMS difference with the tide gauge data to approximately 2 cm. For monthly means, the RMS difference is 1.3 cm. The GPS elevations, of course, can be automatically placed into a well-defined terrestrial reference frame. Ocean tide coefficients, determined from both the GPS and tide gauge data, are in good agreement, with absolute differences below 1 cm for all constituents save K1 and S1. The latter constituent is especially anomalous, probably owing to daily temperature-induced errors in the Aquatrak tide gauge.
Tide prediction machines at the Liverpool Tidal Institute