Bidirectional reflectance characteristics of the sea surface based on midinfrared measured data

Abstract

In order to establish a more realistic radiation model of the sea surface, the effects of solar radiation, sky radiation, and atmospheric thermal radiation on sea surface radiation are taken into consideration, on the basis of which the infrared radiative transfer equation of the sea surface is deduced in this paper. A method for calculating the bidirectional reflection characteristics of the sea surface based on measured data is proposed according to the projection imaging of beam propagation. Based on the measurements of sea surface temperature, incident sky radiation, incident solar radiation, and radiance of sea crests at different times, the radiative transfer equation is used to retrieve the bidirectional reflectance of a midwave infrared sea surface. Meanwhile, the results of the method mentioned above are compared with the calculated results of Cox-Munk, Mermelstein, Wu, and Beckmann bidirectional reflection characteristics models. Research shows that the bidirectional reflectance at the wave crest of a sea surface increases gradually, when the solar incident zenith angle changes from 56.39° to 76.02° as well as the direction of observation remaining constant (θr=80.0°; ϕr=73.0°). The reflection ability at the wave crest of the sea surface is strongest when the incident direction of the sun is close to the observation direction, which is in accordance with the law of reflection. The Cox-Munk model and Wu model are closer to our values when the solar incidence zenith angle is small (θi≤65.93°). On the other hand, the calculated values of the Mermelstein and Wu models are closer to the values in this paper when the solar incidence zenith angle is large (θi≤65.93°). In general, the error of the Beckmann model is a little greater than that of the other three models.