5 Video-Based Wave Direction
Measurement
This chapter discusses the need for implementing a video-based wave
direction measurement system in the physical model setting and describes
procedures followed for making these measurements. Results from the video-
based analysis for each experiment conducted in the idealized coastal inlet
physical model are presented.
Background
In the physical model setting, the primary diagnostic tools to investigate the
complex interaction of incident wind-waves with variations in inlet bathymetry,
engineered inlet structures, and tidal currents are capacitive wave rods and ADV
probes. These instruments are deployed at discrete locations to measure wave
height and current fields. A disadvantage of the application of wave rods and
ADV probes is that they are intrusive and cause localized disturbance in the fluid
motions of the model. To minimize these undesired perturbations, CIRP
implemented a video-based nonintrusive technique to measure wave parameters
accurately with high spatial and temporal resolution. This technique is called the
Coastal Inlets Imaging System (CIIS). Specifically, the CIIS provides
measurements of vector-mean wave direction of wind-wave fields with time- and
space-varying scales observed on the free surface of the model. Measurements
obtained with the CIIS have broad application and can provide quantitative
information for understanding basic coastal inlet process and supporting
computational model development and validation.
During the past decade, video techniques have been developed and applied in
the coastal region to measure variations in hydrodynamic processes (Hathaway
and Bottin 1997; Holland, Holman, and Sallenger 1991; Holland et al. 1995;
Holland and Holman 1996; Holland and Holman 1999; Lippmann and Holman
1991; Stockdon and Holman 2000) and morphologic processes (Konicki and
Holman 2000; Lippmann and Holman 1990; Lippmann, Holman, and Hathaway
1993; Plant and Holman 1997; Ruessink et al. 2000). Development of the CIIS
builds on these photogrammetric and image-processing techniques developed by
the Argus Research Program coordinated by the Coastal Imaging Lab, Oregon
State University (Holman et al. 1993; Aarninkhof and Holman 1999). The
physical model video system consists of obliquely looking monoscopic camera
stations mounted at vantage points above the physical model. Lens distortions,
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Chapter 5 Video-Based Wave Direction Measurement
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