Georeferenced benthic photoquadrats captured annually from 2002-2017, distributed over Heron Reef flat and slope areas.

Full description

Photoquadrats were collected with the purpose of determination of the benthic composition of each photoquadrat for subsequent use as georeferenced field data for calibration and validation purposes of benthic habitat maps derived from remote sensing satellite or airborne imagery. Transect location, direction and depth were chosen to characterise the variation of benthic cover types represented on coral reefs. Photoquadrat interval along the transects was chosen to reflect the resolution of the satellite image data types used. In principle a diver or snorkeler captures a photoquadrat (approximate 1 m2 footprint) of the bottom along a transect at 2 - 3 m intervals. Images were assigned a GPS coordinate and analysed for benthic composition. Initially, from 2002 to 2006, divers/snorkelers swam along a 50 m transect tape. Coordinates were recorded at the beginning and end of the tape. Knowing the horizontal distance interval between photoquadrats the coordinates could be approximated for each image. From 2007 to 2017, divers/snorkelers towed a floating GPS at the surface which was logging position. The coordinates of each photoquadrat were synchronised based on the timestamp of the photoquadrat and the GPS timestamp, using specialised software (e.g. GPS Photo Link www.geospatialexperts.com or DNR Garmin). In principle 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. The camera lens provided a 1 m x 1 m footprint, at a 0.5 m height above the benthos using a plumb line. Horizontal distance between photoquadrats was estimated by fin kicks of the surveyor, and corresponded to a surface distance of approximately 2 - 4 m. For these surveys, the snorkelers traversed a pre-determined transect 250-1000 m in length, varying depending on heterogeneity of the area covered. Divers would conduct 30 min dives along a 5m depth contour, which would be approximately 500-700 m in length. Total of 16 Datasets in Pangaea