Charge-coupled device camera system for remotely measuring the dynamics of ocean waves

Abstract

A camera system has been developed and employed for measuring the dynamics of ocean waves by recording image sequences of reflected sky light. Based on a modified commercially available CCD television camera, tests show that the system is completely free of frame-to-frame smearing and possesses adequate dynamic range for the intended use. A synchronous rotating shutter was also developed which prevents large optical overloads, such as might occur when sun glitter is inadvertently imaged, from causing vertical streaks in the image. The CCD array was found to have significant response nonuniformity. This nonuniformity proved to be less severe than that imposed by nature as a result of the reflection process. A scheme was devised to adequately correct for both using digital techniques. The resolution of the CCD array proved adequate for the oceanographic measurements performed thus far. The power law falloff of the observed radiance fluctuations with (ocean) wave number caused the actual resolution limit of the system to be set by recording system noise rather than CCD array architecture. A three-dimensional wave number-frequency spectrum was computed from a sequence of 256 images. The trend in this spectrum agrees with linear gravity wave dispersion to within 10%.