Aerial images used to test a sundial method for inferring image acquisition time from shadow orientation

This data release provides aerial images acquired through the National Agricultural Imagery Program (NAIP) used to test a method for inferring image acquisition time from shadow orientation. For many applications, such as linking remotely sensed data to streamflow recorded at a gaging station, knowing the time an image is acquired is important, but such metadata often is not available. The sundial method is a simple means of inferring image acquisition time from shadow orientation. Images with known acquisition times are used to test the approach.
 

The file SundialDataReleaseNAIP.csv contains image metadata, shadow measurements, and inferred image acquisition times based on the sundial method. The difference between the known acquisition times of the aerial images and those inferred via the sundial technique is used to assess the accuracy of the method. Please refer to the entity and attribute section of the metadata for further detail regarding this file.
 

To facilitate plotting, this information is also provided in a shapefile that contains the same attributes as the file SundialDataReleaseNAIP.csv but represents the digitized shadows as line features. The shapefile is named ShadowLinesNAIP.shp and is packaged in a zip file named ShadowLinesNAIP.zip. The zip file also contains a .prj file that defines the coordinate reference system of the shapefile as geographic coordinates (latitude and longitude) in the NAD83 datum.


 

The file SundialImagesNAIP.zip contains 6 NAIP aerial images with known acquisition times that were used to test the sundial method. Each image is provided in a GeoTIFF format that includes embedded spatial referencing information.
 

Users are advised to thoroughly read the metadata file associated with this data release to understand the appropriate use and limitations of the data and code provided herein.
 

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