This child data release provides the information needed to download from the USGS EarthExplorer portal digital orthophotos acquired along the Tanana and Nenana Rivers near Nenana, Alaska, on August 19, 2021. The primary goal of this study was to assess the feasibility of estimating surface flow velocities from optical image sequences acquired from a fixed-wing aircraft flying along the river by tracking water surface features via particle image velocimetry (PIV). Remote sensing of flow velocities could provide a more efficient, cost-effective alternative to conventional field-based methods of measuring channel hydraulics and thus become an important component of non-contact approaches to streamgaging. Moreover, the ability to collect such data from a moving aircraft opens up the possibility of examining longer river reaches via remote sensing.
The USGS collaborated with the US Fish and Wildlife Service (USFWS) to acquire digital orthophotography of the Tanana and Nenana Rivers near Nenana, AK, spanning reaches of approximately 4.2 km along the Tanana and 2.7 km along the Nenana. Data were collected at three different flying heights above ground level: 600 m, 902 m, and 1204 m, resulting in 10, 6, and 4 seprate flight lines, respectively. The data from each flying height were nominally referred to as "2K," "3K," and "4k," respectively, for the nominal flying height in feet (2,000, 3,000, or 4,000 feet above ground level). Images were captured using two different systems: a Nikon digital single lens reflex (DSLR) camera that provided standard red-green-blue (RGB) color images and a Lucint multi-camera array that also included a near-infrared band. A GPS point and time stamp associated with each image, along with information on the camera characteristics and a DEM of the study area, were then used as input to the Simactive Correlator 3D photogrammetric software package to produce digital orthophotos in the NAD83_2011 UTM zone 6N projected coordinate system. The pixel sizes of these output images varied among flying heights and between the two imaging systems and ranged from 0.04635 m to 0.1 m. The deliverable products available through this data release include all of the individual orthophotos for each flying height and imaging system as TIFF files with associated *.tfw world files.
The data set delivered by the USFWS was transferred to the USGS Earth Resources Observation and Science (EROS) Center for archiving and distribution via the EarthExplorer web portal at https://earthexplorer.usgs.gov. EROS also produced metadata describing the orthophotos in the files ak21riverorthosmetadata.docx and EROSmetadata.csv.
The orthophotos can can be obtained by visiting the EarthExplorer web site at https://earthexplorer.usgs.gov/and using the Entity ID field in the EROSmetadata.csv file. On the EarthExplorer home page, go to the second tab of the panel on the left, labeled Data Sets, select Aerial Imagery/High Resolution Orthoimagery, and click on Additional Criteria at the bottom. On the Additional Criteria tab, click the plus symbol next to Entity ID, enter the Entity ID value from the EROSmetadata.csv file for the orthophoto of interest, and click on Results at the bottom. The image should then appear in the results tab with several options represented by icons to show the footprint, overlay a browse image, or show the metadata and browse in a separate window. To download the data, click on the fifth icon from the left, which features a green download arrow pointing toward a disk drive, and click Download on the resulting pop-up to begin downloading a zip file. This zip archive contains a number of files in two subfolders. For example, for one of the photos form the Lucint 2K flight line, we have:
1) 4080000_rgb_17pe87_rgb_17pe87_20210819t182335z_00000123.zip\
AK\2021\202108_tanana_ak_lucint_2k_5bnd_5cm_utm6_multi\index001
contains a list of all the images in the data set as a text file, a Word document with general metadata about the entire dataset, an Excel file with spatial information (bounding box) for each orthophoto in the data set, and a *.prj file with information on the projection (NAD83_2011 UTM Zone 6N).
2) 4080000_rgb_17pe87_rgb_17pe87_20210819t182335z_00000123.zip\
AK\2021\202108_tanana_ak_lucint_2k_5bnd_5cm_utm6_multi\vol001
has the actual image as a tif (like rgb_17pe87_rgb_17pe87_20210819t182335z_00000123.tif) and corresponding *.tfw world file (like rgb_17pe87_rgb_17pe87_20210819t182335z_00000123.tfw). Note that vol001 indicates that the images are from the flight line 1, vol002 for fligth line 2, and so on.
These files can be opened and viewed in GIS or image processing software.
