Aerial imagery and structure-from-motion derived data products from UAS survey of the Liberty Island Conservation Bank Wildlands restoration site, Sacramento-San Joaquin Delta, California, October 2018

Unmanned aerial systems (UAS) were used to acquire high-resolution imagery of the Liberty Island Conservation Bank Wildlands restoration site in the Sacramento-San Joaquin Delta in California, with the goal of using structure-from-motion (SfM) photogrammetric techniques to derive a digital surface model, orthomosaic imagery, and a topographic point cloud. The survey was conducted using two Department of Interior-owned 3DR Solo quadcopters fitted with Ricoh GR II digital cameras featuring global shutters. The UAS were flown on pre-programmed autonomous flight lines at an approximate altitude of 120 meters above ground level. The flight lines were oriented roughly east-west and were spaced to provide approximately 66 percent overlap between images from adjacent lines. The cameras were triggered at 1 Hz using a built in intervalometer. Due to the limited UAS battery life, a total of eight flights were required to achieve full coverage of the study area. Before each flight, the camera digital ISO, aperture, and shutter speed were manually set to adjust for ambient light conditions. Although these settings were changed between flights, they were not changed during a flight; thus, the imagery from each flight can be treated as a photo set for photogrammetry purposes. The coordinates of the image acquisition locations were added to the image metadata ('geotagged') during post-processing using the recorded positions from the UAS onboard GPS. A total of 24 temporary ground control points (GCPs) consisting of small square tarps with black-and-white cross patterns were distributed throughout the survey area. The GCP positions were measured using RTK GPS, with real-time corrections from a GPS base station located approximately 3 kilometers south of the study area. This data release presents five data products derived from these surveys which are available for download: 1) an orthomosaic image, 2) a digital surface model (DSM), 3) a topographic point cloud, 4) the geographic positions of the ground control points (GCPs), and 5) the raw imagery in JPG format.