Experimental investigation on bidirectional reflection characteristics of sea foam in the visible and near-infrared bands

The spectral directional reflection characteristics of sea foam have a great influence on ocean color remote sensing and marine environment monitoring. However, due to the difficulty in field measurements, there have little research on the spectral reflection characteristics of sea foam, especially the directional reflection characteristics. In this work, the bidirectional reflectance distribution function (BRDF) of sea foam in the visible and near-infrared bands is experimentally studied through a self-designed scatterometer under laboratory conditions. In the experiments, a self-designed foam generator is employed to generate foam layers with different thicknesses for measurement. Effects of foam layer thickness, incident light wavelength and incident angle on the BRDF·cosθ_r values of foam layer are systemically investigated. The results indicate that the reflection distribution of foam layer presents diffuse reflection characteristics, with BRDF·cosθ_r exhibiting an inverted U-shaped distribution under vertical incidence and a rising peak with increasing incident angles. The thickness of foam has a significant modulation effect on reflectivity, and the peak value of BRDF·cosθ_r increases approximately linearly with the foam layer thickness for vertical incidence. Spectral analysis reveals the BRDF·cosθ_r values decrease with wavelength, attributed to enhanced seawater absorption at longer wavelengths. This study provides basic data and impact mechanism analysis for the directional reflection characteristics of sea foam in the visible and near-infrared bands, and may provide theoretical support for the remote sensing identification and quantitative analysis of sea foam.