New theoretical formulation for the determination of radiance transmittance at the water-air interface.
New theoretical formulation for the determination of radiance transmittance at the water-air interface.
复制标题
测定水-空气界面辐射透射率的新理论公式。
作者：
Pravin Jeba Dev;P. Shanmugam
水-气界面的辐射传输对光学和自然沃茨遥感具有重要意义。从水中发出的向上辐射在通过水-气界面时发生了临界变化。上升流辐射透射率τw，a是发生在水-空气界面处的光学过程，其确定通过界面传播的水中辐射。在以往的研究中，虽然τw，a被简化为一个常数值，但它已被成功地用于确定公海沃茨的离水辐射。常数τw，a值在近岸和内陆环境中的高散射和高吸收沃茨中迅速失效。在这项研究中，我们试图定量地解决上升流辐射透射率τw，a（即，通过水-空气界面逃逸的水中光子的百分比），以在自然沃茨的范围内改变散射和吸收系数。在以往的研究中被忽略的两个重要的光学现象已被充分考虑：（i）粒子的海水折射率（RI）的贡献和（ii）的上升流光子与水-空气界面的多重相互作用。因此，这项研究导致了一个新的理论公式适用于所有自然沃茨的上升流辐射透射率。进一步研究了新公式对近海和内陆沃茨离水辐射率和遥感反射率的影响和变化。特别注意的是还集中在次表面遥感反射率（rrs）到地表以上的遥感反射率（Rrs），这是重要的校准和验证的遥感算法的转换。结果表明，散射沃茨和吸收沃茨的海洋颜色量（Lw和Rrs）的大幅改善高达33%和<5%。
Radiative transfer across the water-air interface has important implications for optics and remote sensing of natural waters. The upward radiance emerging from the water suffers a critical change when it passes through the water-air interface. Upwelling radiance transmittance τw,a is an optical process occurring at the water-air interface that determines the in-water radiances propagating through the interface. In previous studies, τw,a was successfully derived for determining the water-leaving radiances in open ocean waters, despite being oversimplified with a constant value. The constant τw,a value becomes rapidly invalid in high scattering and absorbing waters within nearshore and inland environments. In this study, we attempt to quantitatively solve the upwelling radiance transmittance τw,a (i.e., the percentage of in-water photons that escape through the water-air interface) for varying coefficients of scattering and absorption within the range of natural waters. The two important optical phenomena which are ignored in the previous studies have been fully accounted: (i) the particulate contribution to the refractive index (RI) of seawater and (ii) the multiple interactions of the upwelling photons with the water-air interface. As a result, this study leads to a new theoretical formulation of the upwelling radiance transmittance applicable to all natural waters. The effect and variation of the new formulation on the water-leaving radiance and remote sensing reflectance is further studied for coastal and inland waters. Particular attention is also focused on the conversion of sub-surface remote sensing reflectance (rrs) to above-surface remote sensing reflectance (Rrs), which is important for calibration and validation of the remote sensing algorithms. The results show substantial improvement in the ocean color quantities (Lw and Rrs) by up to factor 33% for scattering waters and <5% for absorbing waters.