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| Study on Bidirectional Reflectance Observation Technology of Underwater Coral |
| XIE Bai-cheng1, 2, XU Zhan-tang1, 3*, YANG Yue-zhong1, 3, ZENG Kai1, 2, ZHANG Yu1, 2, LIU Yong-ming1, 3, ZHOU Wen1, 3, LI Cai1 |
1. State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China
2. University of Chinese Academy of Sciences, Beijing 100049，China
3. Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China
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Abstract As an efficient marine environment monitoring method, remote sensing can simultaneously monitor the distribution and state changes of various substrates on the seabed. Currently, the observation technology of the reflectivity of the bottom substrate is mainly a single angle observation. The accuracy of remote-sensing models to detect the shallow water substrate would be improved significantly by studying and analyzingthe characteristics of multiple-angles reflectance spectra as well as BRDF information of substrates of the seabed in shallow water regions. Using the two-channel simultaneous measurement method, a simple two-way reflectivity measurement system of the seabed is designed, then the characteristic data of fine sandy bottom and Underwater coral were acquired. The results showed that (1) The standard deviation of the reflectance values measured at different azimuth angles for the constant zenith angle (θ=20°, 40° and 60°) of the homogeneous sand on the shore, is less than 1.5% at 400～700 nm. The standard deviation of the reflectance at different zenith angles was analyzed at a constant azimuth angle, and the standard deviation was not more than 1.7%. It indicates that the sand substance on the shore has isotropic characteristics. BRDF characteristics of submarine sandy demonstrated that the standard deviation of the reflectance values, measured at different azimuth angles for the constant zenith angle (θ=20°), showed a relevance increase with the wavelength in the 400～700 nm. The standard deviation of reflectance is 3.8% at 400 nm, while it reaches 12% at 700 nm. It indicates that the submarine sandy also has isotropic characteristics. (2) The standard deviation of the reflectance values measured at different azimuth angles for the constant zenith angle (θ=20°) of corals, gradual increases from 1.1% to 2% at 400～605 nm, then decrease from 2% to 1.2% at 400～605 nm and increases from 1.2% to 4.9% at 675～700 nm. The field test data analysis results show that this underwater bidirectional reflection measurement system can effectively measure the reflection spectrum of various seabed substrates. Based on the measurement data obtained in the field, this study conducts a preliminary analysis of the reflectance spectra of two typical substrates, sandy and coral, which provides spectral characteristics of reflectance at multiple observed angles of various substrates for the subsequent use of remote sensing means to invert the seabed substrates in shallow water areas and dynamically monitor the dynamic changes of the substrates (e. g., coral growth state).
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Received: 2022-03-23
Accepted: 2022-06-21
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Corresponding Authors:
XU Zhan-tang
E-mail: xuzhantang@scsio.ac.cn
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