Wang Menghua
National Oceanic and Atmospheric Administration, National Environmental Satellite, Data, and Information Service, Center for Satellite Applications and Research, Camp Springs, Maryland 20746, USA.
Appl Opt. 2007 Mar 20;46(9):1535-47. doi: 10.1364/ao.46.001535.
In the remote sensing of the ocean near-surface properties, it is essential to derive accurate water-leaving radiance spectra through the process of the atmospheric correction. The atmospheric correction algorithm for Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) and Moderate Resolution Imaging Spectroradiometer (MODIS) uses two near-infrared (NIR) bands at 765 and 865 nm (748 and 869 nm for MODIS) for retrieval of aerosol properties with assumption of the black ocean at the NIR wavelengths. Modifications are implemented to account for some of the NIR ocean contributions for the productive but not very turbid waters. For turbid waters in the coastal regions, however, the ocean could have significant contributions in the NIR, leading to significant errors in the satellite-derived ocean water-leaving radiances. For the shortwave infrared (SWIR) wavelengths (approximately > 1000 nm), water has significantly larger absorption than those for the NIR bands. Thus the black ocean assumption at the SWIR bands is generally valid for turbid waters. In addition, for future sensors, it is also useful to include the UV bands to better quantify the ocean organic and inorganic materials, as well as for help in atmospheric correction. Simulations are carried out to evaluate the performance of atmospheric correction for nonabsorbing and weakly absorbing aerosols using the NIR bands and various combinations of the SWIR bands for deriving the water-leaving radiances at the UV (340 nm) and visible wavelengths. Simulations show that atmospheric correction using the SWIR bands can generally produce results comparable to atmospheric correction using the NIR bands. In particular, the water-leaving radiance at the UV band (340 nm) can also be derived accurately. The results from a sensitivity study for the required sensor noise equivalent reflectance, (NE Delta rho), [or the signal-to-noise ratio (SNR)] for the NIR and SWIR bands are provided and discussed.
在对海洋近表面特性进行遥感时，通过大气校正过程得出准确的离水辐射光谱至关重要。用于海景宽视场传感器（SeaWiFS）和中分辨率成像光谱仪（MODIS）的大气校正算法，利用765和865纳米处的两个近红外（NIR）波段（MODIS为748和869纳米）来反演气溶胶特性，前提是假设近红外波长下的海洋为黑体。已进行修正以考虑近红外波段中一些来自生产力较高但不太浑浊水域的海洋贡献。然而，对于沿海地区的浑浊水域，海洋在近红外波段可能有显著贡献，导致卫星反演的离水辐射存在显著误差。对于短波红外（SWIR）波长（约>1000纳米），水的吸收比近红外波段大得多。因此，短波红外波段的黑体海洋假设通常适用于浑浊水域。此外，对于未来的传感器，纳入紫外波段也有助于更好地量化海洋有机和无机物质，以及辅助大气校正。进行了模拟，以评估使用近红外波段和短波红外波段的各种组合来推导紫外（340纳米）和可见光波长下的离水辐射时，对非吸收性和弱吸收性气溶胶进行大气校正的性能。模拟表明，使用短波红外波段进行大气校正通常能产生与使用近红外波段相当的结果。特别是，紫外波段（340纳米）的离水辐射也能准确推导出来。提供并讨论了对近红外和短波红外波段所需传感器噪声等效反射率（NEΔρ）[或信噪比（SNR）]的敏感性研究结果。
