In order to promote the classification ability of the traditional time-resolved LIF technique to achieve oil spill detection, a novel LIF polarization experimental setup was developed in the laboratory with the ability to obtain time-resolved LIF spectra of both the Co-polarized and Cross-polarized components simultaneously under linearly excitation. With it, a series of oil spills investigation were performed with six crude oil samples, which were carefully selected to ensure each two of them are derived from adjacent wells located within the same well block. After recording of a complete series of time-resolved LIF spectral data, the polarization direction of the excitation was rotated by 90 degrees to proceed with acquisition of another series of data. And with these two sets of data, LIF spectra of the two orthogonal polarization components were calibrated to guarantee the accuracy of the polarization detection. Spectral data of the two orthogonal polarization components were processed with the newly proposed intensity-normalized method and combined to form the data array, based on which clustering and classification results were obtained via the approach of PCA. It was showed that no matter within the three-dimensional space nor the two-dimensional plane composed of the principal components, ideal clustering results can be obtained from similar crude oil samples based on time-resolved LIF polarization technique, even though their locations of fluorescence peak intensities were quite close. Compared with the classification results achieved with the traditional time-resolved LIF technique based on the same data set, it can be concluded that with the auxiliary help of the distinct LIF polarization characteristics of different oil, the classification ability of time-resolved LIF technique is significantly improved.
In complex waters, it is still a challenge to develop ocean color retrieval methods with high accuracy. In this work, we improved an Empirical Orthogonal Function (EOF) method with Equal Dimension New Information (EDNI) to retrieve chlorophyll a concentration (CHL) and phytoplankton absorption coefficient (aph(675)). EDNI was introduced to trace the variations in time-series data. EOF, combined with EDNI, helped to catch input parameters. The data used in this work were collected by optical buoy during a whole red tide in the Zhujiang (Pearl) River Estuary in August 2007. The average absolute percentage difference (APD) of CHL was 29.6%, which was smaller than those from other empirical algorithms. The APD of aph (675) were 23.8%, which was better than those from QAA_v5. In addition, we compared the results with those without EDNI, and found that the APDs of CHL and aph (675) without EDNI increased by about 20%.
Ocean optics discusses the light transmission in seawater, which is a specialty course combining optics and ocean study, and the core course of relevant professional directions. This paper introduces its learning goal and contents. Meanwhile, it also discusses adding study project lecture series and investigating study to realize scientific research back feeding traditional learning. This would further inspire students' interest, cultivate students' innovation and practice ability, and enable them to lay a solid foundation of professional theory.
Mesocosm ecosystem experiment with seawater enclosed of the red tide was carried out from July to September 2001. We got four species of biology whose quantities of bion are dominant in the red tide. During the whole process from the beginning to their dying out for every specie, in situ spectral measurements were carried out. After data processing, characteristic spectra of red tide of different dominant species are got. Via comparison and analysis of characteristics of different spectra, we find that in the band region between 685 and 735 nanometers, spectral characteristics of red tide is apparently different from that of normal water. Compared to spectra of normal water, spectra of red tide have a strong reflectance peak in the above band region. As to spectra of red tide dominated by different species, the situations of reflectance peaks are also different: the second peak of Mesodinium rubrum spectrum lies between 726~732 nm, which is more than 21nm away from the other dominant species spectra’s; Leptocylindrus danicus’s second spectral peak covers 686~694nm; that of Skeletonema costatum lies between 691~693 nm. Chattonella marina’s second spectral peak lies about 703~705 nm. Thus we can try to determine whether red tide has occurred according to its spectral data. In order to monitor the event of red tide and identify the dominant species by the application of the technology of hyperspectral remote sensing, acquiring spectral data of different dominant species of red tide as much as possible becomes a basic work to be achieved for spectral matching, information extraction and so on based on hyperspectral data.
The fine spectra data of red tide can be obtained by airborne hyperspectral red tide monitor. The identification of dominant species of red tide organism by airborne hyperspectral is of great significance for the red tide monitoring.
By making spectral angle analysis and calculating the angle between reflectance of hyperspectral image pixel and that of reference spectra, the similarity of spectra of dominant species to be identified to reference spectra can be determined, and the species of red tide organism whose spectrum makes a smallest angle with the spectra of hyperspectral image pixel is chosen as dominant one.
Reference spectra was measured from the red tide water body during two mesocosm ecosystem experiments and its surrounding water body in August 2002, and the spectra to be identified is the hyperspectral data collected from Bayuquan water body in the Liaodong Bay. By means of spectral angle analysis, red mesodinium rubrum is identified as the dominant species in the red tide on August 25, 2001, which is verified by the synchronous measured data at sea.
It is shown from the study results that the airborne hyperspectral approach to identify the dominant species of red tide is feasible, and will offer valuable service for red tide monitoring.
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