Articles | Volume 5, issue 1
Geosci. Instrum. Method. Data Syst., 5, 17–25, 2016
https://doi.org/10.5194/gi-5-17-2016
Geosci. Instrum. Method. Data Syst., 5, 17–25, 2016
https://doi.org/10.5194/gi-5-17-2016

Research article 05 Feb 2016

Research article | 05 Feb 2016

Removing low-frequency artefacts from Datawell DWR-G4 wave buoy measurements

J.-V. Björkqvist1, H. Pettersson1, L. Laakso1,2, K. K. Kahma1, H. Jokinen1, and P. Kosloff1 J.-V. Björkqvist et al.
  • 1Finnish Meteorological Institute, Helsinki, Finland
  • 2Unit for Environmental Sciences and Management, North-West University, Potchefstroom, Republic of South Africa

Abstract. In this study we describe a previously unreported error in the vertical-displacement time series made with GPS-based Datawell DWR-G4 wave buoys and introduce a simple method to correct the resulting wave spectra. The artefact in the time series is found to resemble a sawtooth wave, which produces an erroneous trend following an f−2 power law in frequency space. The correction method quantifies the amount of erroneous trend below a certain maximum frequency and removes the spurious energy from all frequencies assuming the above-mentioned f−2 power law. The presented correction method is validated against an experimental field test, and its impact on the measured significant wave height is quantified. The method's sensitivity to the choice of the maximum frequency is also briefly discussed.

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Short summary
We identified a previously unknown artefact in the Datawell DWR-G4 wave buoy, which measures the GPS signal to resolve surface water waves. The artefact interferes with the part of the measurements containing information about the longer waves and must be removed to obtain accurate readings. We presented a correction method and found it to be accurate based on a comparison to measurements from a larger wave buoy that measures the movements of the device without using the GPS signal.