Tidal Analysis & Predictions

Tidal analysis and prediction methodologies adhere to rigorous industry standards established by authoritative bodies such as the UKHO (United Kingdom Hydrographic Office).

Quality assurance in tidal analysis involves a systematic approach throughout each phase of data processing. This includes instrument calibration verification, assessment of data for outliers and anomalies, timing accuracy checks, and the application of appropriate harmonic analysis techniques. The selection of harmonic analysis methods depends critically on the quality and duration of input data, with different approaches required depending on the length of observational time series and the presence of data gaps.

Organisations producing official tidal predictions, such as the UK Hydrographic Office, employ specialists with backgrounds in oceanography, physics, mathematics, and marine sciences to perform final quality control reviews. This human oversight ensures predictions meet the exacting standards required for maritime navigation and safety applications, with certification often required for use in commercial shipping operations.

Chart datum is the specific, low-water plane of reference used on nautical charts to define the "zero" mark for water depths (soundings) and tide heights. It is set to the lowest, or near-lowest, predicted tide level (commonly Lowest Astronomical Tide (LAT) in the UK to ensure a safety margin for navigation.

Tidal analysis is the mathematical process of decomposing sea level time series into basic harmonic constituents. The observed tide curve is separated into three components: mean sea level, tidal levels, and surge (residual) levels. This linear regression identifies the amplitude and phase of each tidal constituent, enabling the characterisation of local tidal patterns. The analysis requires a minimum of thirty days of regular sea level measurements to accurately determine the parameters for approximately 36 constituent tides that comprise the observed tide at a specific location.

Tidal harmonic analysis is the mathematical methodology that separates observed tide or tidal current data into its basic harmonic constituents. The process models tidal signals as the sum of a finite set of sinusoids at specific frequencies related to astronomical parameters. Each constituent is identified by its period or speed (measured in degrees per mean solar hour), with the analysis determining amplitude and phase values. This technique enables the prediction of tidal patterns by reconstructing the complex tidal curve from its constituent parts, accounting for both astronomical forces and local bathymetric conditions.