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2006 USDA NAIP County Mosaics Description: Abstract: This data set contains digital ortho-imagery developed to support planning and delivery of USDA programs. The USDA field service centers use digital ortho imagery as a basic reference for conservation plans and soil survey. The imagery has a 1 meter ground sample distance (GSD) ortho imagery rectified to National Mapping Standards at the 1:24,000 scale. Imagery is based on a (7.5 x 15) or (7.5 x11.25) minute quarter quadrangle with a 300 meter buffer on all four sides. Quarter quads imagery is formatted to the UTM coordinate system using NAD83. Each quad may contain as much as 10% cloud cover per tile. This file was generated by compressing quarter quadrangle tiles that cover a project area. MrSID compression, with mosaic option, was used. Target values for the compression ratio are (15:1) and compression levels (9) are used. Purpose: Imagery is used to meet USDA program requirements including conservation planning and soil survey. The interim product is a compressed mosaic. Users should be aware that the interim compressed mosaic may contain defects and have horizontal accuracy less than the specified tolerances. Process_Description: Imagery was flown with Leica ADS40 digital sensors to capture 0.9m raw data. Raw data is then downloaded using Leica GPro software into 12 bit TIFF format. The raw TIFF imagery is then georeferenced and reprojected using GPS/INS 200Hz exterior orientation information (x/y/z/o/p/k) to allow stereo viewable imagery. This stereo viewable imagery is processed with the GPro/LPS automatic point matching algorithm to determine common match points every 2000 pixels across the imagery strip and 333 pixels along strip. This pattern includes dual rows of line ties to the adjacent line of imagery. The resulting point data is imported in Leica ORIMA and used to perform a full bundle adjustment of the imagery point data. Any blunders are removed, and weak areas are manually supplemented to ensure good coverage of points. Once the point data is cleaned and point coverage is acceptable vertical control points from the prior generation MDOQQ's are introduced in the corners and center of the block being adjusted. This control is used to perform any datum shift (x/y/z and rotation) to ensure the new adjusted imagery fits the existing MDOQQ reference imagery. The output from this bundle adjustment process is revised exterior orientation data for the sensor with any GPS/INS, datum, and sensor calibration errors modeled and compensated for. Using this revised EO data orthorectified image strips are created using the USGS DEM. The 10m DEM is used where available and 30m DEM is used elsewhere. The orthorectified strips are overlaid over the existing MDOQQ compressed files to ensure accuracy is met by a visual inspection and manually measuring features. Once the accuracy of the orthorectified image strips are validated the strips are processed with a NWG proprietary dodging package that compensates for the bi-directional reflectance function that is caused by the sun's position relative to the image area. This compensated imagery is then imported into Inpho's OrthoVista 4.0 package which is used for the final radiometric balance, mosaic, and DOQQ sheet creation. These final DOQQ sheets contain a 300m minimum buffer. These final DOQQ tiles are edge inspected to the existing MDOQQ sheets for accuracy validation. The final DOQQ tiles are then organized into directories based on the USDA provided county lists. A visual inspection is performed of the entire county to ensure all tiles are present and the radiometric quality of the county looks good. If the radiometric quality is acceptable the county is compressed to MG3 format using Lizard Tech's GeoExpress v5.0 with a compression factor of 15 and 9 overview levels. Once this compression is complete manual reviewing is performed to ensure satisfactory results. The associated CCM shapefile is created using ESRI ArcView 9.0 with the latest service packs. |
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