Spectral Analysis And Classification Of Coral Reefs Around Qilian Yu In The Xisha Islands

Coral reef has important ecological and economic significance,which is an important habitat for marine organisms.At present,coral reefs are facing the fate of the rapid degeneration and death,it not only seriously affects the living environment of coral reef benthic organisms,but also brought huge economic losses to mankind.Remote sensing technology,as a large scale,real time earth observation technology,is an effective method to obtain the information of coral reefs,However,the similarity and diversity of the spectral reflectance of the bottom sediments of coral reefs will seriously affect the results of remote sensing monitoring,therefore,it is necessary to study the characteristics of the spectral reflectance of the bottom sediments of coral reefs,which is also the basic work for the coral reef remote sensing research work.At present,the hotspot and difficulty of coral reef remote sensing research is to identify and distinguish the cover types of sediment from the perspective of spectroscopy.In this paper,the sea around of Qilian Yu in Xisha Islands as the study area,and extraction of the main features of coral reef sediments for spectral measurement and analysis,study the reflection spectral characteristics of the coral reef sediments.At the same time,based on the different spectral characteristics,differential transformation,principal component analysis and support vector machine model are used to identify and distinguish the main types of coral reef sediments,the main results are as follows:(1)The investigation of coral reef around study area,have a preliminary understanding of the composition of benthic organisms and the living environment of the typical coral reefs in the study area,collecting the samples such as Ahermatypic coral,algae,sea grass and other calcareous sand for coral reef spectral analysis.The spectrum database of coral reef was established in the surrounding area of study area,and the stone corals,soft coral,seaweed,calcareous sand,starfish and sponge were collected in this spectral database.Stone coral includes a variety of major coral species such as staghorn coral,cup coral,and rose coral.We measured the surface spectral curve at the same time,the surface of the substrate types are mainly the coral,sand,seaweed,rocks,etc.At present,a total of 105 sediment samples and 44 water surface spectra are stored in the database,which provides the basic data for the analysis of the spectral characteristics of coral reefs in the study area.(2)Spectral differences exist between different sediments in the coral reef surrounding the study area,to spectral analysis of healthy coral,coral bleaching,algae,sea grass,the dead coral covered of algae and calcareous sand.The reflectance of calcareous sand is higher than others in visible light bands.The simple and smooth spectral curve is the most easily distinguished.Albino coral due to loss of pigment in vivo,the original spectral reflectance increases,there are different degrees of fluctuation between 400-700 nm spectrum bands.the absorption peak of 450-550 nm and 675 nm are increased obviously.In 350-375 nm,500nm,560-610 nm,675nm and 700 nm bands,the two order derivative of the healthy coral spectrum is significantly different.The two order derivative of alga and sea grass is different in 440-460 nm,505-520 nm,560-610 nm and the vicinity of 675 nm spectral band.The two order derivative spectrum curve of the dead coral covered by algae and algae is very close,but there is a difference in amplitude,in 560-600 nm and 650-700 nm the concavity and convexity of the two order derivative of algae are more severe.In 510 nm,575nm,680-690 nm and 700-710 nm spectral band,the two order derivative curve of the dead coral covered with seaweed and algae can be distinguished.(3)The spectral distinguish of different growth states of coral,to analysis of two derivative spectra of healthy coral and albino coral,the shape of spectral curve are opposite in the vicinity of 550 nm,570nm,610 nm,625nm band.There are differences in the two order derivative spectra of healthy coral and albino coral,between 350-525 nm and 650-700 nm,healthy coral and albino coral can be separated according to these spectral features.At the same time,the spectral curves of albino coral in the study area are regular,in this paper,according to the spectral characteristics and the different degrees of coral bleaching,the albino coral was divided into 4 stages: early coral bleaching,coral bleaching metaphase,serious coral bleaching and dead coral covered by algae,and the spectral characteristics of different coral bleaching stages are summarized.(4)The principal component analysis(PCA)and support vector machine(SVM)model were used to classify the dead coral in healthy coral,albino coral and algae.The PCA analysis results show,most of the variance is explained in the first principal component,the load of three spectral is relatively high,healthy coral is 94.4%,albino coral is 84.5%,dead coral covered by algae is 91.8%.Indicates that there is a limited variation within the same state spectral data set,it is considered that the first principal component is a representative spectrum in the data set.The results of SVM modeling and classification show that the accuracy of the original spectral reflectance model have the highest precision is 92.86%.13 of the 14 test samples were classified correctly,and the one classification errors were analyzed in detail.