Quantitative visualization of geophysical flows using low-cost oblique digital time-lapse imaging

Estuaries and coastal waters are regions where many different important physical processes can be found. Although the physical scale of these processes is often relatively small, their time scales are correspondingly rapid and aliasing is usually a problem in sampling programs. There can be significant spatial variations in mixing and flow patterns, which are usually learned only through long experience in a particular region. Observational and interpretation difficulties might be significantly simplified with a simple remote sensing tool to be used in conjunction with standard techniques. Here, the use of digital time-lapse photography at highly oblique angles as a tool for,flow visualization is discussed. The interaction of surface waves with slicks and internal motions can cause apparent changes in the shade and color of water at shallow angles in a way not apparent in downlooking views. The use of time-lapse techniques allows us to isolate time scales of interest and, by ``speeding up{''} low-frequency motions, causes them to become more apparent to the eye. A cheap and portable system based on commercially available equipment is described and various advantages and shortcomings are discussed. Results are shown to illustrate the utility of the observational system.