An unmanned aerial system (UAS) was used to acquire high-resolution imagery of the intertidal zone at Puget Creek and Dickman Mill Park in Tacoma, Washington on June 3, 2019. This imagery was processed using structure-from-motion (SfM) photogrammetric techniques to derive high-resolution digital surface models (DSM), orthomosaic imagery, and topographic point clouds.
In order to maximize the extent of the subaerially exposed area, the survey was timed to coincide with a spring low tide occurring at approximately 18:36 Universal Coordinated Time (UTC) (11:36 Pacific Daylight Time (PDT)), with an observed water level of -1.47 meters relative to the NAVD88 vertical datum at the Tacoma NOAA tide station (station ID 9446484).
One acquisition flight was conducted at each site: flight F01 covered the Puget Creek area and was conducted between 18:43 and 18:54 UTC (11:43 and 11:54 PDT); flight F02 covered the Dickman Mill Park area and was conducted between 19:24 and 19:37 UTC (12:24 and 12:37 PDT).
The flights were conducted using a Department of Interior-owned 3DR Solo quadcopter 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), resulting in a nominal ground-sample-distance (GSD) of 1.3 centimeters per pixel. 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. Before each flight, the camera's digital ISO, aperture, and shutter speed were adjusted for ambient light conditions.
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 ("TACO") located approximately 5 kilometers from the study area which is operated by the Washington State Reference Network (WSRN).
This data release presents five data products derived from these surveys which are available for download: 1) orthomosaic images with a resolution of 1.3 centimeters per pixel, 2) digital surface models (DSM) and hillshade images with a resolution of 2.5 centimeters per pixel, 3) topographic point clouds in LAZ format 4) the geographic positions of the ground control points, and 5) the raw aerial imagery in JPG format.
|Title||Aerial imagery and structure-from-motion data products from UAS survey of the intertidal zone at Puget Creek and Dickman Mill Park, Ruston Way, Tacoma, WA, June 2019|
|Authors||Joshua B Logan, Eric E Grossman, Nathan R VanArendonk, Liam Horner|
|Product Type||Data Release|
|Record Source||USGS Digital Object Identifier Catalog|
|USGS Organization||Pacific Coastal and Marine Science Center|