An unmanned aerial system (UAS) was used to acquire high-resolution imagery of the intertidal zone at Lone Tree Point, Kiket Bay, Washington on June 5, 2019. This imagery was processed using structure-from-motion (SfM) photogrammetric techniques to derive a high-resolution digital surface model (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 20:19 Universal Coordinated Time (UTC) (13:19 Pacific Daylight Time (PDT)), with a predicted water level of -0.69 meters below mean lower-low water (MLLW) at the Sneeoosh Point NOAA harmonic tide station (station ID 9448576).
A total of five flights were conducted for the survey between 19:29 and 20:36 UTC (12:29 and 13:36 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 camera was mounted using a fixed mount on the bottom of the UAS and oriented in an approximately nadir orientation. For flights F01, F02, F03, and F04, the UAS was flown on pre-programmed autonomous flight lines at an approximate altitude of 70 meters above ground level (AGL), resulting in a nominal ground-sample-distance (GSD) of 1.8 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. For flight F05, the UAS was flown manually to acquire imagery over areas not mapped in the previous flights. For all flights, 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.
Eighteen temporary ground control points (GCPs) were distributed throughout the 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 ("SKGT") located approximately 16 kilometers from the study area 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) an orthomosaic image with a resolution of 2 centimeters per-pixel, 2) a digital surface model (DSM) and a hillshade image with a resolution of 4 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 Lone Tree Point, Kiket Bay, WA, June 2019|
|Authors||Joshua Logan, Eric E Grossman, Nathan R VanArendonk|
|Product Type||Data Release|
|Record Source||USGS Digital Object Identifier Catalog|
|USGS Organization||Pacific Coastal and Marine Science Center|