基于无人机SfM摄影测量的潮间带牡蛎礁地貌调查

Geomorphological survey of intertidal oyster reefs based on UAV Structure-from-Motion photogrammetry

牡蛎礁是一种重要的海岸地貌系统,礁体的空间分布格局,深刻影响着周围的水动力和沉积动力过程,进而反作用于牡蛎礁自身演化。江苏海门蛎蚜山牡蛎礁为中国海岸重要且稀有的生态系统,近年来,沉积物覆盖和人为捕捞导致牡蛎礁退化严重。本文利用无人机对蛎蚜山牡蛎礁进行地貌观测,基于运动恢复结构(SfM,Structure from Motion)摄影测量技术重建出航拍区域的高分辨率三维模型,包括正射影像和数字高程模型(DEM),并对重建的模型进行目视解译和剖面分析。结果表明,位于航拍区域的牡蛎礁主要有三种形态:条带状、斑块状和环状。条带状牡蛎礁脊线整体上呈南北走向,可能由环状牡蛎礁退化或牡蛎的生物自组织过程形成。航拍区域的地貌面高差可达5 m以上,地势最高处高程为0.5 m(85高程,下同),最低处高程为−4.7 m。礁区内的礁体仍处于退化状态,其演化过程主要为:礁体表面出现坑洼→坑洼进一步扩张、延伸→形成溶槽→礁体分隔、分解,同时伴有沉积物对礁体的掩埋。本研究表明,无人机SfM技术可以高效获取牡蛎礁的地貌信息,为研究牡蛎礁演化过程提供了有力支持。

Oyster reefs is an important coastal morphological system,the spatial distribution pattern of the reefs profoundly influences the surrounding hydrodynamic and sedimentary processes,which in turn affects the evolution of oyster reefs.The Liyashan oyster reef in Haimen,Jiangsu,is an important and rare ecosystem in the Chinese coast;however,it has been seriously degraded by sediment cover and human fishing in recent years.A geomorphological observation of the oyster reefs in Liyashan was carried out using an unmanned aerial vehicle(UAV).Based on the SfM(Structure from Motion)photogrammetry,high-resolution three-dimensional models of the aerial photography region were reconstructed,including orthophoto and digital elevation model(DEM).Then,the visual interpretation and profile analysis on the reconstructed models were conducted.Results show that the oyster reefs are mainly composed of three types in distribution shape:string,patch,and ring.The“string”oyster reef ridges are generally oriented north-south,likely were formed by the degradation of“ring”reefs or self-organization process of oysters.The elevation differences within the surveyed area could reach more than 5 m,the highest elevation was 0.5 m(1985 national elevation),while the lowest elevation was−4.7 m.The reefs are still in a degraded state,and the evolutionary process is mainly as follows:potholes appear on the surfaces of the reefs→further expansion and extension of potholes→formation of grooves→segmentation and disintegration of the reefs,accompanied by sedimentary burial of the reefs.This study shows that the UAV SfM technique can efficiently obtain geomorphological data of oyster reefs,which provides a strong support for studying the evolution of oyster reefs.