Abstract
Both surface-reflected daylight and upwelling light are modeled to second order to help provide a quantitative and physically interpretable description of daylight imagery of ocean surface waves for wave spectra. An image recording of the slope-modulated reflected and upwelled radiance can be optically analyzed to provide the surface slope spectrum as a function of wavenumber for a particular patch on the ocean surface.
Sources of error involved in obtaining ocean spectral information from daylight imagery are outlined and methods of alleviating them discussed. Errors resulting from the nonlinear nature of the transfer function relating wave slope to radiance at the, sensor are, shown to be minimized using the second-order theory in evaluating potential sensor geometries. The directional sensitivity of daylight imagery to waves traveling in various directions is also evaluated.
A modified Pierson wave spectrum was used to generate numerically a one-dimensional wave-slope profile. This slope profile was used as input to a numerical model that generated a modulation of radiance at the sensor. The spectrum of this radiance modulation agreed favorably with the original Pierson spectrum.
