Coral Reef Monitoring Research Remote Sensing

As one of the world’s ecosystems, coral reefs are facing a major crisis under the influence of global climate change and human activities, and it may become the first extinct ecosystem over the word on account of global warming. Remote sensing techniques, as a rapid and periodic investigation and monitoring tool, has being widely applied in coral reefs research. It is of great significance to establish a remote sensing method on coral reefs investigation and monitoring to protect the ecosystem effectively.It takes Xuwen coral reef protection zoon of state level as research area, discusses the four aspects such as underwater topography remote sensing inversion, spectrum characteristics analysis, substrate classification and image change detection. The conclusions are as follows:(1) It established the remote sensing inversion model of coral reef underwater topography based on the satellite image data and field survey data, divided the underwater ecoregion by using the water depth thematic map and landform characteristic of coral reef, and described the underwater topography on a macro point of view by remote sensing interpret. The research shows that the remote sensing inversion method of water depth has good feasibility on coral reef underwater topography.(2) After spectral measurement and feature analysis of different substrates, it shows that there are three spectral regions on reflectance diagram, the high reflection area (400-580nm), fast attenuation area (580-740nm) and low reflection area (740-900nm) in general. The water depth and quality have greater influence on the spectrum, and the spectrum feature of substrates are significant different. There are some spectrum differences between dominant species of coral,and spectrum between healthy and bleaching state of a kind of coral also have obvious difference, it can be more accurate to find the difference through the first order differential of spectrum. But for different corals of a sibling, the distinction of spectrum is subtle. It’s difficult to find the nuances even through the first order differential method. It simulated the spectral response of ETM+, Quick Bird, IKONOS and SPOT5by spectral response function, and the result shows that these sensors are suitable for simple classification. For more detailed classification, it maybe needs to use hyper-spectral data. The research laid a solid theoretical basis for coral reef remote sensing and also provided a gist for image data choice.(3) On the basic of water depth inversion method, it presented a method to identify large coral reefs after researching on coral reefs information extraction. Results show that the method can identify potential large coral reefs although the precision of this method is not high. This method has some limitations in practical application. Based on spectral characteristics, it applied QuickBird image to achieve a simple classification of substrates. It compared the results of supervised and non-supervised classification. The research shows that corals that been identified are mainly distributed in the near shore area near1km, and the shallow depth of2meters. The accuracy of supervised classification is about71%, which is higher than unsupervised classification. Influenced by water depth and remote sensing data, the precision of substrate information extraction has yet to be further improve, but it provides a new thought and technical reference for follow-up study.(4)It researched a spatial autocorrelation statistics method for multi-date images based on the spatial feature of coral reefs. It applied the spatial autocorrelation statistics method to analysis the TM image data of2004,2007and2010at Xuwen coral reef protection zone. The result shows that local area of images showed the evident change in the statistical characteristics of spatial during the year2004to2010, the change on low and high space zones are obvious, and performed the overall trends within the study area. It analyzed and explained the four field investigation points between2004and2010, and proved that the method is feasible. In addition, influenced by consecutive years of strong typhoons, a lot of dead coral debris and mud sand mixture are eroded over near shore area, and it shows obvious homogeneity trend in spatial statistic analysis. Coral reef ecosystems affected by natural disasters is obvious. It proved that the method is a simple and practical method for change detection with low cost and is not sensitive to factors such as water depth at last.This thesis studies the remote sensing monitoring method of coral reefs, discussed the feasibility of remote sensing method applied on coral reef resources investigation and dynamic monitoring. Because of the strong regional characteristics of coral reef ecosystem, in spite of achieving some preliminary results of Xuwen coral reef protection area, we still need further research in underwater spectral analysis, physical model, water quality influence, multi-source remote sensing etc.