南海环礁发育过程中形成了开放程度不同的环礁类型, 依据环礁不同地貌部位的几何因子作为反映环礁开放程度的指标可以定量划分环礁开放程度类型。如果将澙湖潮汐通道作为环礁地貌结构要素用来反映环礁开放程度, 则潮汐通道可以成为新的度量因子。利用高分辨率遥感影像结合GIS技术, 以澙湖潮汐通道的几何参数为主构建反映环礁开放程度的模型, 结果表明, 以口门宽度与礁体中轴线长度之比为指标建立的经验式, 可用来划分环礁开放程度类型, 封闭型环礁的开放度为0, 准封闭型环礁的开放度为0~0.06, 半开放型环礁的开放度为0.06~0.25, 开放型岛礁的开放度为0.25~1。因此, 采用这一量化表达式反映南海环礁的开放程度类型, 可为珊瑚环礁的开放程度发育规律研究提供科学工具。

All coral atolls consist of several facies zones. Tidal inlet, which is the channel to connect the lagoon and the sea, has different geometric shapes. According to different angle and principle, coral atolls have been classified into various types. In order to identify the open type of atolls quantificationally, two geometric parameters of tidal inlet are regarded as new metrical factors to construct a new expression. The new description function is the ratio of tidal inlet’s width to atoll’s midline. Finally, the threshold division of the atolls’ type is formed on the basis of the new expression. The threshold result shows that the open degree of the enclosed atolls is 0, the contiguous enclosed atolls is between 0 and 0.06, the half-opening atolls’ is between 0.06 and 0.25, and the opening atolls’ is between 0.25 and 1. Thus, the new function can be used to reflect the openness of different atolls for development regularity of coral atolls in the South China Sea.