RESUMEN
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%.
RESUMEN
Slope spectral density resolved in wave number and direction is an important statistical descriptor of water surface waves. Experimentalists have estimated this descriptor from optical wave imagery by assuming that light from the surface is modulated linearly by the component of wave slope aligned with the imaging azimuth. The level of error arising from this assumption of linearity depends on the optical conditions and can be severe. We have numerically explored this error when only reflected radiance is imaged by using a synthesized sea surface and a clear sky model to simulate sea surface imaging. Additionally, we have developed a method for identifying geometries which minimize nonlinearity. This paper describes our analytic models, our numerical techniques, and the character of our results.
RESUMEN
A reflectometer is described that extends the continuous measurement of the near-normal-incidence reflectance of solids to vacuum ultraviolet (vuv) wavelengths. Clean reflecting surfaces are achieved by in situ sample preparation and ultrahigh vacuum environment. The low intensity problem is solved with electronic lock-in amplification. The over-all instrument has an absolute error of reflectance of (DeltaR/R)(Absolute) = +/-0.03. The precision is estimated to be (DeltaR/R)(Relative) = +/-0.002 or better. The wavelength range of 1100 A to 7000 A is covered. Some representative results show that this design provides substantial improvement in sensitivity and resolution of vuv reflectance measurements.
