2011 Vermont NAIP Digital Ortho Photo Imagery

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Digital Georectified Image. | Source Geospatial Form: remote-sensing image | Type of Source Media: UnKnown

The imagery was collected using ADS40-SH52 digital sensors.\n

Collection was performed using a combination of twin-engine\n

aircraft flying at an average flying height of 17500 and\n

27000 ft above mean terrain, with nominal sidelap of 21%,\n

giving the collected data nominal ground sampling distance\n

of 0.55 and 0.75 meters. Based-upon the CCD Array\n

configuration present in the ADS40 digital sensor, imagery\n

for each flight line is 12,000-pixels in width. Red, Green,\n

Blue, Near-Infrared and Panchromatic image bands were\n

collected.\n

Collected data was downloaded to portable hard drives and\n

shipped to the processing facility daily. Raw flight data\n

was extracted from external data drives using GPro software.\n

Airborne GPS / IMU data was post-processed using IPAS, PosPac\n

and/or TerraPos software and reviewed to ensure sufficient\n

accuracy for project requirements.\n

Using Pictovera software, planar rectified images were\n

generated from the collected data for use in image quality\n

review. The planar rectified images were generated at five\n

meter resolution using a two standard deviation histogram\n

stretch. Factors considered during this review included but\n

were not limited to the presence of smoke and/or cloud cover,\n

contrails, light conditions, sun glint and any sensor or\n

hardware-related issues that potentially could result in\n

faulty data. When necessary, image strips identified as not\n

meeting image quality specifications were re-flown to obtain\n

suitable imagery.\n

Aerotriangulation blocks were defined primarily by order of\n

acquisition and consisted of four to seventeen strips.\n

Image tie points providing the observations for the least\n

squares bundle adjustment were selected from the images using\n

an autocorrelation algorithm. Photogrammetric control points\n

consisted of photo identifiable control points, collected\n

using GPS field survey techniques. The control points were\n

loaded in to a softcopy workstation and measured in the\n

acquired image strips. A least squares bundle adjustment\n

of image pass points, control points and the ABGPS was\n

performed to develop an aerotriangulation solution for each\n

block using Pictovera software. Upon final bundle\n

adjustment, the triangulated strips were ortho-rectified to\n

the USGS NED DEM for the project area. The images were\n

re-sampled from the raw resolution of 0.55 or 0.75 meters to\n

the required resolution of 1.0 meters.\n

Positional accuracy was reviewed in the rectified imagery\n

by visually verifying the horizontal positioning of the\n

known photo-identifiable survey locations using ArcGIS\n

software.\n

The red, green, blue, and NIR bands were combined to\n

generate a final ortho-rectified image strip. The ADS40\n

sensor collects twelve bit image data which requires\n

radiometric adjustment for output in standard eight bit\n

image channels. The ortho-rectified image strips were\n

produced with the full 12 bit data range, allowing\n

radiometric adjustment to 8 bit range to be performed on\n

a strip by strip basis during the final mosaicking steps.\n

The imagery was mosaicked using manual seamline generation\n

in Orthovista Seam Editor (OVSE). The 12 bit data range was\n

adjusted for display in standard eight bit image channels by\n

defining a piecewise histogram stretch using OrthoVista\n

software. A constant stretch was defined for each image\n

collection period, and then strip by strip adjustments were\n

made as needed to account for changes in sun angle and\n

azimuth during the collection period. Strip adjustments were\n

also made to match the strips histograms as closely as\n

possible to APFO specified histogram metrics and color\n

balance requirements. Automated balancing algorithms\n

were applied to account for bi-directional reflectance as\n

a final step before the conversion to 8 bit data range.\n

APFO specified DOQQs were extracted from the final mosaic\n

in GeoTIFF format. 4-Band DOQQs were produced and 3-B