Georeferenced photographs of benthic photoquadrats acquired over seven reefs in the Mackay to Capricorn region of the Great Barrier Reef, May, 2019

Underwater georeferenced photo-transect surveys were conducted at different locations: in the shallow waters of the Reef Flat (0.5-2.5m) by a snorkeller, or, along a 5m depth contour of the Reef Slope by a diver. For these surveys, the snorkellers or divers traversed a pre-determined transect 250-1000 m in length, 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 photoquadrats was estimated by fin kicks of the surveyor, and corresponded to a surface distance of approximately 2.0 - 4.0 m. The coordinates of each photoquadrat were approximated based on the timestamp of the photoquadrat and the GPS timestamp, using custom software. Coordinates of each photoquadrat were interpolated by finding the GPS coordinates that were logged at a set time before and after the photoquadrat was captured. Photoquadrats were collected with the purpose of determination of the benthic composition of each photoquadrat and to subsequently use this georeferenced field data for calibration and validation of benthic habitat maps. Transect location, direction and depth were chosen for this purpose and so as to characterise the variation in benthic cover types present on coral reefs. Photoquadrat interval along the transects was chosen to reflect the resolution of high spatial resolution satellite image data types.

水下地理参考照片样带调查（Underwater georeferenced photo-transect surveys）在不同地点开展：由浮潜员在礁坪（Reef Flat）浅水区（0.5-2.5m）进行，或由潜水员沿礁坡（Reef Slope）5m等深线开展。在调查过程中，浮潜员或潜水员沿预先设定的、长度为250-1000m的样带行进，同时使用标准数码相机在设定高度拍摄底栖生物（benthos），并拖曳一个水面浮标GPS（surface float GPS）——该设备每5秒记录一次轨迹。当相机镜头距底栖生物0.5m高度时，其拍摄足迹（footprint）为1.0m×1.0m。照片样方（photoquadrat）之间的水平距离通过调查人员的鳍踢次数估算，对应水面距离约为2.0-4.0m。利用定制软件，基于照片样方的时间戳和GPS时间戳，对每个照片样方的坐标进行近似计算。通过查找照片样方拍摄前后设定时间记录的GPS坐标，对每个照片样方的坐标进行插值（interpolation）。收集照片样方的目的在于确定每个样方的底栖组成，并将这些地理参考野外数据用于底栖生境图的校准（calibration）和验证（validation）。样带的位置、方向和深度选择既服务于上述目的，也旨在表征珊瑚礁上底栖覆盖类型（benthic cover type）的变化。样带上照片样方的间隔选择旨在匹配高空间分辨率卫星影像（high spatial resolution satellite image）的数据分辨率。