Morel Yann G, Favoretto Fabio
Retired, BP 2862 98703 Punaauia, French Polynesia.
Posgrado en Ciencias Marinas y Costeras (CIMACO) Universidad Autonoma de Baja California Sur, La Paz Baja California Sur 23080, Mexico.
Sensors (Basel). 2017 Jul 21;17(7):1682. doi: 10.3390/s17071682.
All empirical water column correction methods have consistently been reported to require existing depth sounding data for the purpose of calibrating a simple depth retrieval model; they yield poor results over very bright or very dark bottoms. In contrast, we set out to (i) use only the relative radiance data in the image along with published data, and several new assumptions; (ii) in order to specify and operate the simplified radiative transfer equation (RTE); (iii) for the purpose of retrieving both the satellite derived bathymetry (SDB) and the water column corrected spectral reflectance over shallow seabeds. Sea truth regressions show that SDB depths retrieved by the method only need tide correction. Therefore it shall be demonstrated that, under such new assumptions, there is no need for (i) formal atmospheric correction; (ii) conversion of relative radiance into calibrated reflectance; or (iii) existing depth sounding data, to specify the simplified RTE and produce both SDB and spectral water column corrected radiance ready for bottom typing. Moreover, the use of the panchromatic band for that purpose is introduced. Altogether, we named this process the Self-Calibrated Supervised Spectral Shallow-sea Modeler (4SM). This approach requires a trained practitioner, though, to produce its results within hours of downloading the raw image. The ideal raw image should be a "near-nadir" view, exhibit homogeneous atmosphere and water column, include some coverage of optically deep waters and bare land, and lend itself to quality removal of haze, atmospheric adjacency effect, and sun/sky glint.
据一致报道，所有经验性水柱校正方法都需要现有的深度探测数据来校准一个简单的深度反演模型；在非常明亮或非常黑暗的海底上，它们的效果很差。相比之下，我们着手：（i）仅使用图像中的相对辐射数据以及已发表的数据和几个新假设；（ii）为了指定并运用简化的辐射传输方程（RTE）；（iii）为了在浅海海底反演卫星衍生测深（SDB）和水柱校正后的光谱反射率。海况真值回归表明，用该方法反演的SDB深度仅需进行潮汐校正。因此，应当证明，在这些新假设下，无需（i）进行正式的大气校正；（ii）将相对辐射转换为校准后的反射率；或（iii）现有的深度探测数据，来指定简化的RTE并生成可供海底类型识别的SDB和经水柱校正的光谱辐射。此外，还引入了为此目的使用全色波段。总之，我们将这个过程命名为自校准监督光谱浅海建模器（4SM）。不过，这种方法需要训练有素的从业者在下载原始图像后的数小时内得出结果。理想的原始图像应是“近天底”视图，呈现均匀的大气和水柱，包括一些光学深水区域和裸地的覆盖范围，并且便于对雾霭、大气邻接效应以及太阳/天空耀光进行高质量去除。
