Extracting coastal variables from video images: short to medium-term coastal processes

Abstract

The swash zone is that part of the beach alternately covered and exposed by uprush and backwash. The time scale of swash motion is highly variable. In this way, the swash zone is characterized by strong and unsteady flows, high turbulence levels, large sediment transport rates and rapid morphological change. The objective of this work is the study of the dynamic of this region through the investigation of the controlling processes (runup, swash, and setup) and their consequences on sedimentary dynamics of the ambient. This study will be accomplished through the use of video images from Argus system. The Argus System was developed by the Coastal Imaging Laboratory (CIL) at Oregon State University, in United States. A Argus station has one or more cameras connected in a computer with processing images system. These cameras are directed obliquely to cover the coastal area of interest. It will be used a system with five digital cameras of higher resolution. The cameras were installed on the roof of the Hotel Brisa at Massaguaçú beach - São Paulo. Instantaneous oblique images (snapshots) are acquired every 30 minutes of daylight for each camera, at a rate of 2 Hz during sampling intervals of 10 minutes. Mean and variance are calculated from the intensities of brightness of each pixel in the corresponding 1200 frames acquired at intervals, creating an image of long exposure (Timex) and one of the variance (variance). In the image processing the data are called pixel time series and it represents a key to key reduction the data flow required to make a number of optical measurements in the nearshore. The power of pixel time series comes not so much from the individual pixel time series, but from the coherent analysis from an array of pixels whose number and locations are appropriate for a desired type of measurement. Such arrays, often based on designs developed for in situ sensors, are called pixel instruments. The pixels arrays on the swash zone are cross-shore transects of contiguous pixels. The pixel temporal series or timestacks are digitized using a semiautomated algorithm developed by Coastal Imaging Laboratory (CIL) and after the calculation, the data are converted to time series of water level elevation measured relative to mean sea level. In this way, it is hoped through this study provide scientific support to the understanding of the processes controlling the dynamics of swash and its consequences for the adjacent regions. Monitoring by the Argus system will allow a general characterization of the study area in different weather conditions, waves and tides.