Comparison of Visual Observations of Wave Height and Period to Measurements Made by an Offshore Slope Array

Nathaniel G. Plant, Gary B. Griggs

Abstract


Records of littoral environment parameters such as wave height, period, and direction are essential to nearshore process studies. The most detailed studies require an elaborate and expensive array of current meters and wave gauges, which allow high resolution spectral analysis of wave and current variability. Studies concerned with low frequency variability or relatively large stretches of coastline may not be able to afford or even need high resolution spectral analyses. Incident wave parameters of study sites that lack offshore wave gauges can be characterized with data collected by human observers from the shoreline (SMITH and WAGNER, 1991). However, without documentation of observational accuracy, human observations provide only a relative comparison of daily littoral environment conditions. These observations become more useful to researchers when confidence limits can be assigned to the data, allowing their applicability to specific projects to be evaluated. This study compares simultaneous observations made by two observers over a four month period. The study period comprised enough observations to determine confidence limits about estimates of wave heights ranging from 1 to 4 meters and periods ranging from 5 to 20 seconds. These statistics broaden the range of previous statistical comparisons. As in previous studies (SCHNElDER and WEGGEL, 1980; PERLlN, 1984), observers tend to overestimate the period of short period waves, underestimate the period of long period waves, and underestimate wave height as incident wave height increases.


Keywords


Visual observations; wave gauge; wave height; wave period

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