Aerial imagery from UAS survey of the Liberty Island Conservation Bank Wildlands restoration site, Sacramento-San Joaquin Delta, California, 2018-10-23

Aerial imagery was collected using two Department of Interior owned 3DR Solo quadcopters fitted with Ricoh GR II digital cameras featuring global shutters. The cameras were mounted using a fixed mount on the bottom of the UAS and oriented in a roughly nadir orientation. 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, and were programmed to simultaneously acquire imagery in both JPG and camera raw (Adobe DNG) formats. Due to the limited UAS battery life, a total of 8 flights were required to achieve full coverage of the study area. The flights were conducted on 2018-10-23 between 18:21 and 20:35 Universal Coordinated Time (UTC) (11:21 and 13:35 Pacific Daylight Time (PDT)). 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 permitted to change during a flight; thus, the images from each individual flight were acquired with consistent camera settings.

The image files were renamed using a custom python script. The file names were formed using the following pattern Fx-YYYYMMDDThhmmssZ_Ryz.*, where: - Fx = Flight number - YYYYMMDDThhmmssZ = date and time in the ISO 8601 standard, where 'T' separates the date from the time, and 'Z' denotes UTC ('Zulu') time. - Ry = RA or RB to distinguish camera 'RicohA' from 'RicohB' - z = original image name assigned by camera during acquisition - * = file extension (JPG or DNG)
The approximate image acquisition coordinates were added to the image metadata (EXIF) ('geotagged') using the image timestamp and the telemetry logs from the UAS onboard single-frequency 1-Hz autonomous GPS. The geotagging process was done using GeoSetter software. To improve timestamp accuracy, the image acquisition times were adjusted to true ('corrected') UTC time by comparing the image timestamps with several images taken of a smartphone app ('Emerald Time') showing accurate time from Network Time Protocol (NTP) servers. For RicohA no image time adjustment was needed; for RicohB, +00:00:02 (2 seconds) were added to the image time to synchronize with corrected UTC time. The positions stored in the EXIF are in geographic coordinates referenced to the WGS84(G1150) coordinate reference system (EPSG:7660), with elevation in meters relative to the WGS84 ellipsoid.
Additional information was added to the EXIF using the command-line 'exiftool' software with the following command: exiftool ^ -P ^ -Copyright="Public Domain. Please credit U.S. Geological Survey." ^ -CopyrightNotice="Public Domain. Please credit U.S. Geological Survey." ^ -ImageDescription="Low-altitude aerial image of the Liberty Island Conservation Bank Wildlands restoration site, Cache Slough Complex, Sacramento-San Joaquin Delta, California, USA, from USGS survey 2018-676-FA" ^ -Caption-Abstract="Liberty Island Conservation Bank Wildlands restoration site, Cache Slough Complex, Sacramento-San Joaquin Delta, California, USA, from USGS survey 2018-676-FA" ^ -Caption="Liberty Island Conservation Bank Wildlands restoration site, Cache Slough Complex, Sacramento-San Joaquin Delta, California, USA, from survey 2018-676-FA" ^ -sep ", " ^ -keywords="Liberty Island, Liberty Island Conservation Bank, Wildlands restoration site, Cache Slough Complex, Sacramento-San Joaquin Delta, California, 2018-676-FA, Unmanned Aircraft System, UAS, aerial imagery, USGS, Pacific Coastal and Marine Science Center" ^ -comment="Low-altitude aerial image from USGS Unmanned Aircraft System (UAS) survey 2018-676-FA" ^ -Credit="U.S. Geological Survey" ^ -Contact="pcmsc_data@usgs.gov" ^ -Artist="Pacific Coastal and Marine Science Center"

Edited metadata to add keywords section with USGS persistent identifier as theme keyword. No data were changed.