Modeling of the mid-wave infrared radiation characteristics of the sea surface based on measured data

Sea surface infrared emissivity is an important parameter in oceanic remote sensing and it is difficult to measure directly. An analytical model is proposed to calculate the sea surface emissivity based on the infrared radiation theory. Emphasis is placed on the infrared radiative transfer equation deduced from the theoretical analysis of sea surface emissivity. The spectral emissivity, reflectivity, and atmospheric path radiance are then calculated based on an experimental measurement of the sea surface temperature, the spectral radiance of the sky, and the sea surface infrared images at different times. The infrared radiation model of sea surface established in this paper is verified by an example that shows self-consistency by putting the inferred emissivity into a radiative transfer model. The experimental results demonstrate that the sea surface emissivity can be expressed as ε = 0.6457 ± 0.0103 when the detection angle (θ) is 80.0° under a low wind speed. The self- radiation of the sea surface in the 3-5 μm region is ten times as large as the reflected radiation and approximately three to four times greater than the atmospheric path radiance. Comparisons between the calculated values of the Fresnel equations and the experimental results demonstrate the feasibility of the analytical model proposed in this paper.