Orthomosaic imagery for the intertidal zone at Puget Creek and Dickman Mill Park, Tacoma, WA, 2019-06-03

This portion of the data release presents a high-resolution orthomosaic images of the intertidal zones at Puget Creek and Dickman Mill Park, Tacoma, WA. The orthomosaics have a resolution of 1.3 centimeters per pixel and were derived from structure-from-motion (SfM) processing of aerial imagery collected with an unmanned aerial system (UAS) on 2019-06-03. The raw imagery used to create the orthomosaics was acquired using a UAS fitted with a Ricoh GR II digital camera featuring a global shutter. The UAS was flown on pre-programmed autonomous flight lines at an approximate altitude of 50 meters above ground level (AGL). The flight lines were oriented roughly shore-parallel and were spaced to provide approximately 70 percent overlap between images from adjacent lines. The camera was triggered at 1 Hz using a built-in intervalometer. The imagery was geotagged using positions from the UAS onboard single-frequency autonomous GPS. Twelve temporary ground control points (GCPs) were distributed throughout each survey area to establish survey control. The GCPs consisted of a combination of small square tarps with black-and-white cross patterns and "X" marks placed on the ground using temporary chalk. The GCP positions were measured using post-processed kinematic (PPK) GPS, using corrections from a GPS base station located approximately 5 kilometers from the study area. The orthomosaic images are provided at a resolution of 1.3 centimeters per pixel, in a three-band RGB format, with 8-bit unsigned integer values compressed using high-quality JPEG compression. The images have been formatted as cloud optimized GeoTIFFs with internal overviews and masks to facilitate cloud-based queries and display. For file naming purposes the spatial resolution has been rounded to the nearest centimeter in the file names (for instance, the 1.3-cm resolution Puget Creek orthomosaic is named PugetCreek_2019-06-03_orthomosaic_1cm.tif).