Extracting long waves from tide-gauge records

The data processing required to extract long waves from tide-gauge data is described and applied to three diverse but typical examples: meteorologically generated long waves (rissaga), far infragravity waves, and tsunami. The steps are: detiding, despiking, degapping, high-pass filtering, and denoising. Orthogonal wavelet decomposition is used for despiking, high-pass filtering, and denoising. This has the advantage that it can be used for nonstationary data such as rissaga and tsunami because the basis function (the mother wavelet) is localized. The long-wave extraction method has evolved from development of real-time systems for monitoring long waves for navigation purposes. Using the technique, there are hundreds of modern tide gauges around the world (every major port has one) whose data could be used to monitor long waves that affect navigation and cause a hazard.