Lee ZhongPing, Carder Kendall L, Du KePing
Naval Research Laboratory, Code 7333, Stennis Space Center, Mississippi 39529, USA.
Appl Opt. 2004 Sep 1;43(25):4957-64. doi: 10.1364/ao.43.004957.
For optically deep waters, remote-sensing reflectance (r(rs)) is traditionally expressed as the ratio of the backscattering coefficient (b(b)) to the sum of absorption and backscattering coefficients (a + b(b)) that multiples a model parameter (g, or the so-called f'/Q). Parameter g is further expressed as a function of b(b)/(a + b(b)) (or b(b)/a) to account for its variation that is due to multiple scattering. With such an approach, the same g value will be derived for different a and b(b) values that provide the same ratio. Because g is partially a measure of the angular distribution of upwelling light, and the angular distribution from molecular scattering is quite different from that of particle scattering; g values are expected to vary with different scattering distributions even if the b(b)/a ratios are the same. In this study, after numerically demonstrating the effects of molecular and particle scatterings on the values of g, an innovative r(rs) model is developed. This new model expresses r(rs) in two separate terms: one governed by the phase function of molecular scattering and one governed by the phase function of particle scattering, with a model parameter introduced for each term. In this way the phase function effects from molecular and particle scatterings are explicitly separated and accounted for. This new model provides an analytical tool to understand and quantify the phase-function effects on r(rs), and a platform to calculate r(rs) spectrum quickly and accurately that is required for remote-sensing applications.
对于光学深度较大的水体，传统上遥感反射率（r(rs)）表示为后向散射系数（b(b)）与吸收系数和后向散射系数之和（a + b(b)）的比值，并乘以一个模型参数（g，即所谓的f'/Q）。参数g进一步表示为b(b)/(a + b(b))（或b(b)/a）的函数，以考虑其因多次散射而产生的变化。采用这种方法，对于提供相同比值的不同a和b(b)值，将得出相同的g值。由于g部分衡量了向上光的角度分布，且分子散射的角度分布与粒子散射的角度分布有很大不同；即使b(b)/a比值相同，g值也预计会因不同的散射分布而变化。在本研究中，通过数值演示分子和粒子散射对g值的影响后，开发了一种创新的r(rs)模型。这个新模型将r(rs)表示为两个独立的项：一项由分子散射的相位函数控制，另一项由粒子散射的相位函数控制，并且为每个项引入了一个模型参数。通过这种方式，分子和粒子散射的相位函数效应被明确分离并得到考虑。这个新模型提供了一个分析工具来理解和量化相位函数对r(rs)的影响，以及一个用于快速准确计算遥感应用所需的r(rs)光谱的平台。
