The NHAP photography were acquired at 40,000 feet above mean terrain and flight lines were centered on the 1:24,000-scale USGS map series. Two different camera systems were used; a 6 inch focal length lens was used to acquire B/W film at an approximate scale of 1:80,000 and an 8.25 inch lens was used to acquire CIR film at an approximate scale of 1:58,000.The NHAP film rolls were scanned at USDA FPAC BC GEO BRANCH using high resolution aerial roll film scanners. The images were scanned at a resolution of 12.5 microns (approximately 0.75 m GSD) in three spectral bands (RGB). The individual image scans were provided to USDA FPAC BC GEO BRANCH for post processing into orthorectified image mosaics. USDA FPAC BC GEO BRANCH also provided nominal photo center coordinates for each image along with the camera calibration information. The USGS NED 10m DTM for CONUS was used in the orthorectification process. The output orthomosaic tiles are rendered as a target resolution of 0.75m GSD and are delivered in a WGS 1984 UTM grid projection for which the majority of the cell footprint falls. The orthomosaic cells have a designed overlap of 40 pixels on all sides. The delivered orthomosaics have a target horizontal accuracy when measured against the NAIP imagery of +/- 10m. Control point information was derived from USDA FPAC BC GEO BRANCH provided control point files or from the reference NAIP imagery. Elevations for the control points were interpolated from the NED 10m elevation model. There was no attempt to color balance the mosaic images. Thus, significant differences in color, including striping between adjacent flight lines and images is present in the mosaics. Where multiple images were collected for a single design photo center, the newest available scan was used. The files are delivered uncompressed. Note that there are some areas that were not collected in the NHAP program collections.

Purpose: Provide NHAP historic aerial imagery for GIS-Remote Sensing use.

Creation Date: 20200211

Publication Date: 20200430

Revision Date: 20250106

Refresh Cycle: As new imagery becomes available.

Version: 1.10.0

Change Log: Service deployed.

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