Radiative Transfer Properties In Dispersed Particulate Medium In The Upper Ocean Generated By Breaking Waves

Dispersed particulate medium are widely found in the natural and industrial production processes,such as the sea foam layer and underwater bubble layer created by high wind speeds and breaking gravity waves,the foam layer produced in the glass melting process,the spectral selective coatings,crystal materials and thin films composed of dense micro-nanoparticles.At present,various theoretical and experimental studies have been carried out on the radiative transfer properties in dispersed particulate medium.However,there are still some crutial technical problems to be studied under many application conditions.For example with respect to the atmosphere-cean interface layer,in the visible and near-infrared regions,the bubble layer in the upper ocean is a multicomponent,non-uniform dispersed particulate medium composed of dense bubbles and seawater.The sea foam layer is a weak absorption dispersed particulate medium composed of densely packed,hollow bubbles with water shells.In the microwave region,due to the strong absorption property of seawater and the size parameters of bubbles close to the incident wavelength,the dependent scattering effect cannot be neglected,the sea foam layer is a strong absorption dense dispersed particulate medium composed of coated bubbles with meso-micro size parameters.In this paper,the dispersed particulate medium composed of bubble layer in the upper ocean and sea foam layer are studied.Firstly,in the visible and near-infrared regions,the radiative transfer properties of a multi-component,non-uniform dispersed particulate medium are investigated theoretically,the influences of the bubble layer and sea foam layer on the radiative transfer in the atmosphere-ocean systems are evaluated.Secondly,taking the dense polystreye standard microspheres,sea foam layer in the microwave regions and dense micro-nano bubbles for which the dependent scattering effect cannot be neglected as research objects,the effects of multiple scattering and dependent scattering on the radiative transfer properties of dense dispersed particulate medium are investigated.The main tasks are listed below:The bubble layer in the upper ocean is a multi-component,non-uniform semitransparent medium composed of dense coated bubbles,pure seawater,colored dissolved organic matter,phytoplankton and inorganic particles.The bubbles in seawater may affect the radiative transfer process in the upper ocean,which can have an important effect on the accuracy of ocean color remote sensing and underwater detection,and so on.In this paper,the influence of the absorption of the medium on the apparent radiative characteristics of the bubbles is studied based on the generalized Mie theory.It is found that the influence of the absorption of the medium increases with the increase of the bubble size parameter,and the influence cannot be neglected when the wavelength is greater than 2?m.In addition,a radiative transfer model which accurately considers the radiative properties of the components of the bubble layer in the upper ocean is provided in this paper.The effects of bubble coating,bubble number density and chlorophyll concentrations(Chl)on the spectral reflectance and bidirectional reflectance distribution function of the bubble layer in the upper ocean are investigated.The results show that the bubble populations have a significant impact on the spectral reflection characteristics of the bubble layer due to the strong backscattering of the bubbles that are coated with an organic film.The spectral reflectance and BRDF×cosqr can increase to 11.5 and 2.27 times compared to the clear water(Chl = 0.01 mg×m-3)without bubbles,and the effects of bubble scattering are diminishing as the seawater becomes turbid.Compared with seawater with no bubbles,the spectral reflectance and BRDF·cos?r values in case of normal incidence can increase to 11.5 and 2.27 times in clear waters when Chl =0.01 mg·m-3.As water becomes turbid,the effect of bubble populations on the enhanced reflectance gradually decreases.The sea foam layer locating at atmosphere-ocean interface is composed of the whitecaps formed by wind-driven sea waves and the foam produced due to the underwater bubbles floating up to the surface.In this paper,the sea foam layer was treated as a densely packed large-scale particle system composed of hollow spherical bubbles with water shells based on the latest research progress in the field of microwave remote sensing.A sea foam model composed of coated bubbles with different particle radii and void fractions was established through some simplifications.The spectral radiative properties of the sea foam layer were calculated using a Mie code which is suitable for coated spheres with large size paremeters.In the framework of independent scattering theory,the spectral reflectance and BRDF of the sea foam layer from visible to near-infrared spectral ranges were calculated by Monte Carlo method.The accuracy and feasibility of the proposed model were verified by comparing with the existing theoretical models and experimental data.The results show that the sea foam layer can significantly increase the spectral reflectance and BRDF.Due to the strong scattering characteristics of the foam layer,the effects of subsurface scattering and wind speed on the spectral reflectance and BRDF can be neglected in most cases,except for a very thin foam layer.Increasing foam layer thickness and solar zenith angle increases the spectral reflection characteristics of the foam layer.However,increasing the mean radii of air bubbles decreases the spectral reflection characteristics.For the sea foam layer in the microwave regions,due to the size parameters of bubbles close to the incident wavelength,dependent scattering effects between the dense bubbles increase obviously,the calculation results of the radiation transfer equation based on the independent scattering approximation will be no longer reliable when the particle concentration increases to a certain extent.In this paper,we focused on the dense polystreye standard microspheres,sea foam layer in the microwave regions and dense micro-nano bubbles.The dependent scattering effects between particles were characterized by the Percus–Yevick hard sphere model,and the dependent scattering effects on the radiative properties and radiative transfer properties of dense dispersed particulate medium were investigated.The Mueller matrix of randomly distributed,densely packed discrete spheres were comparatively studied based on Maxwell theory and radiative transfer theory,respectively.The correction efficiency and application of the Percus–Yevick hard sphere model were evaluated.The results show that the PercusYevick hard sphere model shows good accuracy in accounting for the far-field interference effects when the size parameter is less than or equal to 6.964 and the phase shift is less than or equal to 2.72.The radiative transfer characteristics of the dense particle system composed of polystyrene standard microspheres were studied by both theoretical and experimental methods.The accuracy of the model was also verified by comparing the calculated and measured the bidirectional scattering distribution function.The results show that the dependent scattering effect has significant effects on smaller particles and the optical thin medium.With the increase of the optical thickness of dense particle systems,the effect of dependent scattering is obviously weakened.The sea foam layer in the microwave regions presents strong absorption and weak scattering properties,the BRDF·cos?r values of the sea foam layer at different solar zenith angles decreases obviously due to the dependent scattering effects.