Benthic and substrate cover data derived from a time series of photo-transect surveys for the Eastern Banks, Moreton Bay Australia, 2004-2014. Dataset #846147

For these surveys, a snorkeler(s) swam over the bottom while taking photos of the benthos at a set height using a standard digital camera and towing a surface float GPS which was logging its track every five seconds. The camera lens provided a 1.0 m x 1.0 m footprint, at 0.5 m height above the benthos. Horizontal distance between photos was estimated by fin kicks of the survey snorkeler, and corresponded to a surface distance of approximately 2.0 - 4.0 m.
Approximation of coordinates of each benthic photo was done based on the photo timestamp and GPS coordinate time stamp, using GPS Photo Link Software (www.geospatialexperts.com). Coordinates of each photo were interpolated by finding the gps coordinates that were logged at a set time before and after the photo was captured.
Dominant benthic or substrate cover type was assigned to each photo by placing 24 points random over each image using the Coral Point Count excel program (Kohler and Gill, 2006). Each point was then assigned a dominant cover type. Using a benthic cover type classification scheme containing seven first-level categories (seagrass, seagrass plus, macro algae calcareous, macro algae non calcareous, cyanobacteria and other algae, substratum, and, other) and 41 subcategories.
Benthic cover composition summaries of each photo were generated automatically in CPCe. The resulting benthic cover data for each photo was linked to gps coordinates, saved as an ArcMap point shapefile, and projected to Universal Transverse Mercator WGS84 Zone 56 South.

本项调查中，浮潜者（snorkeler）沿水底行进，以固定高度使用标准数码相机拍摄底栖生物（benthos），同时拖拽一台搭载GPS的水面浮标，该GPS每5秒记录一次自身轨迹。该相机镜头在距底栖生物0.5米高度时，拍摄视场幅面为1.0米×1.0米。照片间的水平距离通过调查浮潜者的蛙踢次数估算，对应水面距离约为2.0至4.0米。

本研究借助GPS Photo Link软件（网址：www.geospatialexperts.com），依据照片拍摄时间戳（timestamp）与GPS坐标时间戳（timestamp），对每张底栖生物照片的坐标进行近似估算。通过查找照片拍摄前后预设时间点记录的GPS坐标，对每张照片的坐标进行插值计算。

本研究采用Coral Point Count Excel程序（Kohler与Gill，2006），在每张图像上随机放置24个采样点，以此为每张照片指定优势底栖生物或基质覆盖类型，随后为每个采样点赋予具体的优势覆盖类型。本研究采用的底栖生物覆盖类型分类体系包含7个一级类别（海草（seagrass）、附加海草（seagrass plus）、钙化大型藻类（macro algae calcareous）、非钙化大型藻类（macro algae non calcareous）、蓝细菌与其他藻类（cyanobacteria and other algae）、基质（substratum）及其他（other））与41个子类别。

借助CPCe软件可自动生成每张照片的底栖生物覆盖组成总结结果。最终得到的每张照片底栖覆盖数据将与GPS坐标关联，保存为ArcMap点形状文件（shapefile），并投影至WGS84坐标系下的南56带通用横轴墨卡托（Universal Transverse Mercator）投影带。