| Description |
This portion of the data release presents raw aerial imagery collected during an unoccupied aerial system (UAS) survey of the coral reef off Waiakane, Molokai, Hawaii, on 24 June 2018. The imagery was acquired using a Department of Interior-owned 3DR Solo quadcopter fitted with a Ricoh GR II digital camera featuring a global shutter. The camera was mounted in a nadir orientation using a fixed mount. Before each flight, the camera’s digital ISO, aperture, and shutter speed were adjusted for ambient light conditions. The UAS was flown on pre-programmed autonomous flight lines spaced to provide approximately 75 percent overlap between images from adjacent lines. The UAS was flown at an approximate altitude of 100 meters above ground level (AGL), resulting in a nominal ground-sample-distance (GSD) of 2.6 centimeters per pixel. The camera was triggered at 1 Hz using a built-in intervalometer. A total of five flights were conducted for the survey between 16:40 and 17:45 UTC (06:40 and 07:45 HST). Flight F01 was a reconnaissance flight, and no mapping imagery was collected. Flights F02 and F03 were conducted at an approximate altitude of 100 meters above ground level (AGL), resulting in complete coverage of the mapping area with a nominal ground-sample-distance (GSD) of approximately 2.5 centimeters per pixel. Flights F04 and F05 were conducted using the same flight lines and altitudes of F02 and F03, but the camera was fitted with a circular polarizing filter to reduced reflections and provide improved imaging of the seafloor through the water surface. After acquisition, the images were renamed to include flight number and acquisition time in the file name. The coordinates of the approximate image acquisition location were added ('geotagged') to the image metadata (EXIF) using the telemetry log from the UAS onboard single-frequency autonomous GPS. The image EXIF was also updated to include additional information related to the acquisition. Although the images were recorded in both JPG and camera raw (Adobe DNG) formats, only the JPG images are provided in this data release. The data release includes a total of 1,665 JPG images. Images from takeoff and landing sequences were not used for processing and have been omitted from the data release. The images from each flight are provided in a zip file named with the flight number. The zip files containing the imagery collected with the circular polarizing filter are named with '_CPF' to distinguish them from the files with imagery collected without a filter. [More]
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