Abstract
Increasingly, LiDAR has more and more applications. However, so far, there are no relevant publications on using airborne LiDAR for ocean optical profiling in the South China Sea (SCS). The applicability of airborne LiDAR for optical profiling in the SCS will be presented. A total of four airborne LiDAR flight experiments were conducted over autumn 2017 and spring 2018 in the SCS. A hybrid retrieval method will be presented here, which incorporates a Klett method to obtain LiDAR attenuation coefficient and a perturbation retrieval method for a volume scattering function at 180°. The correlation coefficient between the LiDAR-derived results and the traditional measurements was 0.7. The mean absolute relative error (MAE) and the normalized root mean square deviation (NRMSD) between the two are both between 10% and 12%. Subsequently, the vertical structure of the LiDAR-retrieved attenuation and backscattering along airborne LiDAR flight tracks was mapped. In addition to this, ocean subsurface phytoplankton layers were detected between 10 to 20 m depths along the flight track in Sanya Bay. Primary results demonstrated that our airborne LiDAR has an independent ability to survey and characterize ocean optical structure.
Highlights
Satellite ocean color remote sensing has expanded and refined our knowledge of global phytoplankton ecosystems, the ocean carbon cycle, and the ocean’s role in climate change
That was due to the water surface reflection and photomultiplier tube (PMT) transient response effect, and little water backscatter could be detected by the receiver
Our results indicated that the airborne LiDAR technique is feasible and effective for ocean optical profiling in the South China Sea (SCS)
Summary
Satellite ocean color remote sensing has expanded and refined our knowledge of global phytoplankton ecosystems, the ocean carbon cycle, and the ocean’s role in climate change. Passive remote sensing has inherent limitations to resolve water vertical structure [1]. One method is to separate molecules and Mie scatter using the High-Spectral-Resolution LiDAR (HSRL) technique. HSRL systems are often complex and expensive. Another approach is to assume that the ratio of LiDAR extinction-to-backscatter is known [18]. The slope method [19] is often used in homogenous mediums, while the Fernald [20] and Klett [21] methods have been widely used in inhomogeneous mediums All these methods need the LiDAR ratio, which is very difficult to accurately obtain, especially in the sea with such a complex environment. A theoretical development suggests that this might be a useful technique for the ocean, but actual data showed a lot of variability [22]
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