Airborne hyperspectral remote sensing technique has advantages of flexibility, wide coverage and high spatial and spectral resolution, so is suitable for the coastal water environment monitoring. This paper summarizes the techniques and their applications of marine airborne hyperspectral remote sensing in China. As far as the techniques are concerned, the characteristics of PHI, a spectrometer imager fit for marine application are introduced. Concerning applications, with an aim at the difficulties in airborne remote sensing monitoring, such as the identification of red tide organism species, detection of oil film and the calculation of sea ice intensity, a detailed description is given to the application level of airborne hyperspectral remote sensing in China. Based on the requirement of national marine environment and disaster monitoring and the development trend of marine airborne sensing, the operational application prospect of marine airborne hyperspectral remote sensing is given.
The red tide spectrum database is the basis and prerequisite for red tide hyperspectral remote sensing, a technical support for the field investigation on red tide and the main technical measure for red tide data management and application. The data in the database mentioned in this paper come mainly from the red tide mesocosm experiment, and include the simultaneously collected biological, chemical, hydrographic and meteorological data besides the spectrum data of red tide dominant species. The database has not only the conventional functions for data query, retrieval and plotting, but also the algorithmic functions for the ground object spectrum data processing in the Visual FoxPro system environment and the biological information extraction using the ground object spectrum data.
This system is not only an effective application system for detecting the red tide organism, identifying the red tide dominant species and analyzing the characteristic amount of red tide organism, but also a powerful tool for the marine environmental protection and the red tide disaster reduction in the future.
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.
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.