3.1 Measuring Wind-driven Wave Properties in a Coastal Estuary

Monday, 11 January 2016: 4:00 PM
Room 342 ( New Orleans Ernest N. Morial Convention Center)
Jeff Colvin, Florida Institute of Technology, Melbourne, FL; and S. M. Lazarus, M. Splitt, and B. P. Holman

Wind and wave measurements are sparse along and within the Indian River Lagoon (IRL), a long, narrow, and shallow estuary on central Florida's east coast. The lack of observations is problematic for model validation as well as for understanding the physical processes that impact erosion such as wave generation. This investigation uses a GoPro camera and the principles of photogrammetry in lieu of more expensive alternatives, such as buoys, to determine wave characteristics (speed, height, and period) in the IRL. Combined with wind, fetch, and bathymetry data, these measurements can help verify wave height predictions. This work complements an estuary set-up project funded by the NOAA CSTAR program to bring the Nearshore Wave Prediction System into the coastal zone.

The GoPro camera was mounted on a low tripod near the water surface level and video was recorded for about 30 minutes at 60 frames per second. Simultaneous measurements of wind speed and direction were also recorded with a wind LIDAR. Algorithms were written to 1) capture still frames from the video at a given frame rate, 2) strip the center column of pixels from each image, and 3) combine these stripped columns of pixels together, in time sequence, to create a new image called a timestack. The timestack has dimensions of height on the y-axis and time on the x-axis. The code also rectifies the image pixels with respect to height using information from images with stadia rods that are placed at varying distances from the camera setup. This allows the real world height to be calculated from the vertical pixels in the timestack image. Wave speed, wave height, and wave period can be easily extracted from a properly rectified timestack image.

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