Georeferenced photographs of benthic photoquadrats acquired along 160 transects distributed over 23 reefs in the Cairns to Cooktown region of the Great Barrier Reef, January and April/May, 2017

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 GPS Photo Link Software (www.geospatialexperts.com). 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.
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