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首页> 外文期刊>Applied optics >HOW WELL CAN RADIANCE REFLECTED FROM THE OCEAN-ATMOSPHERE SYSTEM BE PREDICTED FROM MEASUREMENTS AT THE SEA SURFACE
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HOW WELL CAN RADIANCE REFLECTED FROM THE OCEAN-ATMOSPHERE SYSTEM BE PREDICTED FROM MEASUREMENTS AT THE SEA SURFACE

机译：从海洋表面的测量值可以预测海洋-大气系统反射的辐射如何

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There is interest in the prediction of the top-of-the-atmosphere (TOA) reflectance of the ocean-atmosphere system for in-orbit calibration of ocean color sensors. With the use of simulations, we examine the accuracy one could expect in estimating the reflectance rho(T) of the ocean-atmosphere system based on a measurement suite carried out at the sea surface, i.e., a measurement of the normalized sky radiance rho(B) and the aerosol optical thickness (tau(a)), under ideal conditions-a cloud-free, horizontally homogeneous atmosphere. Briefly, rho(B) and tau(a) are inserted into a multiple-scattering inversion algorithm to retrieve the aerosol optical properties-the single-scattering albedo and the scattering phase function. These retrieved quantities are then inserted into the radiative transfer equation to predict rho(T) Most of the simulations were carried out in the near infrared (865 nm), where a larger fraction of rho(T) is contributed by aerosol scattering compared with molecular scattering, than in the visible, and where the water-leaving radiance can be neglected. The simulations suggest that rho(T) can be predicted with an uncertainty typically less than or similar to 1% when the rho(B) and tau(a) measurements are error free. We investigated the influence of the simplifying assumptions that were made in the inversion-prediction process, such as modeling the atmosphere as a plane-parallel medium, using a smooth sea surface in the inversion algorithm, using the scalar radiative transfer theory, and assuming that the aerosol was confined to a thin layer just above the sea surface. In most cases, these assumptions did not increase the error beyond +/-1%. An exception was the use of the scalar radiative transfer theory, for which the error grew to as much as similar to 2.5%, suggesting that the use of rho(B) inversion and rho(T) prediction codes that include polarization would be more appropriate. However, their use would necessitate measurement of the polarization associated with rho(B). We also investigated the uncertainty introduced by an unknown aerosol vertical structure and found it to be negligible if the aerosols were nonabsorbing or weakly absorbing. An extension of the analysis to the blue, which requires measurement of the water-leaving radiance, showed significantly better predictions of rho(T) because the major portion of rho(T) is the result of molecular scattering, which is known precisely: We also simulated the influence of calibration errors in both the Sun photometer and the rho(B) radiometer. The results suggest that the relative error in the predicted rho(T) is similar in magnitude to that in rho(B) (actually it was somewhat less). However, the relative error in rho(T) induced by error in tau(a) is usually much less than the relative error in tau(a). Currently, it appears that radiometers can be calibrated with an uncertainty of similar to+/-2.5%, therefore it is reasonable to conclude that, at present, the most important error source in the prediction of rho(T) from rho(B) is likely to be error in the rho(B) measurement. (C) 1996 Optical Society of America [References: 30]
机译：对于在轨校准海洋颜色传感器的海洋-大气系统的最高大气（TOA）反射率的预测引起了人们的兴趣。通过使用模拟，我们检验了在海面进行测量的基础上，即在对海洋大气系统的反射率rho（T）进行估算（即对归一化的天空辐射度rho（ B）和气溶胶光学厚度（tau（a）），在理想条件下-无云，水平均匀的气氛。简而言之，将rho（B）和tau（a）插入到多散射反演算法中，以检索气溶胶的光学特性-单散射反照率和散射相位函数。然后将这些取回的量插入到辐射传递方程中以预测rho（T）大部分模拟是在近红外（865 nm）下进行的，其中与分子相比，气溶胶散射对rho（T）的贡献更大散射，而不是可见光和可以忽略不计的水辐射。仿真表明，当rho（B）和tau（a）测量无误差时，可以以通常小于或类似于1％的不确定性预测rho（T）。我们研究了在反演预测过程中做出的简化假设的影响，例如，将大气建模为平面平行介质，在反演算法中使用光滑海面，使用标量辐射传递理论，并假设气溶胶被限制在海面上方的薄层中。在大多数情况下，这些假设不会使误差增加超过+/- 1％。一个例外是使用了标量辐射传递理论，该理论的误差高达2.5％，这表明使用包括极化的rho（B）反演和rho（T）预测代码会更合适。 。但是，使用它们将需要测量与rho（B）相关的极化。我们还研究了未知的气溶胶垂直结构所带来的不确定性，发现如果气溶胶不吸收或吸收较弱，则可以忽略不计。将分析扩展到蓝色（需要测量出水的辐射度）​​可以更好地预测rho（T），因为rho（T）的主要部分是分子散射的结果，这是众所周知的：还模拟了太阳光度计和rho（B）辐射计中校准误差的影响。结果表明，预测的rho（T）的相对误差在幅度上与rho（B）的相对误差相似（实际上略小）。但是，由tau（a）的误差引起的rho（T）的相对误差通常比tau（a）的相对误差小得多。当前，似乎可以用大约+/- 2.5％的不确定度校准辐射计，因此可以合理地得出结论，目前，从rho（B）预测rho（T）中最重要的误差源是可能是rho（B）测量中的错误。 （C）1996年美国眼镜学会[参考：30]

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