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USDA NAIP 2007 Orthoimagery Projection: UTM NAD83 Format: MrSid Resolution: 1 or 2 Meter Description: This data set contains imagery from the National Agriculture Imagery Program (NAIP). NAIP acquires digital ortho imagery during the agricultural growing seasons in the continental U.S.. A primary goal of the NAIP program is to enable availability of ortho imagery within one year of acquisition. NAIP provides four main products: 1 meter ground sample distance (GSD) ortho imagery rectified to a horizontal accuracy of within +/- 5 meters of reference digital ortho quarter quads (DOQQ's) from the National Digital Ortho Program (NDOP); 2 meter GSD ortho imagery rectified to within +/- 10 meters of reference DOQQs; 1 meter GSD ortho imagery rectified to within +/- 6 meters to true ground; and, 2 meter GSD ortho imagery rectified to within +/- 10 meters to true ground. The tiling format of NAIP imagery is based on a 3.75' x 3.75' quarter quadrangle with a 300 meter buffer on all four sides. NAIP quarter quads are formatted to the UTM coordinate system using NAD83. NAIP imagery may contain as much as 10% cloud cover per tile. This file was generated by compressing NAIP quarter quadrangle tiles that cover a county. MrSID compression, with mosaic option, was used. Target values for the compression ratio are (15:1) and maximum number of compression levels are used. Purpose: NAIP imagery is available for distribution within 60 days of the end of a flying season and is intended to provide current information of agricultural conditions in support of USDA farm programs. For USDA Farm Service Agency, the 1 meter GSD product provides an ortho image base for Common Land Unit boundaries and other data sets. The 1 meter NAIP imagery is generally acquired in projects covering full states in cooperation with state government and other federal agencies who use the imagery for a variety of purposes including land use planning and natural resource assessment. With an annual cycle, NAIP is also used for disaster response often providing the most current pre-event imagery. While suitable for a variety of uses the 2 meter GSD NAIP imagery is primarily intended to assess crop condition and compliance to USDA farm program conditions. The 2 meter imagery is generally acquired only for agricultural areas within state projects. Process_Description: Color Digital imagery was collected with a Leica ADS40 Digital Sensor. The ADS40 CCD array includes 12,000 pixels across track at 6.5 microns. The digital imagery was acquired with a minimum of 20% sidelap, then processed using Leica software to produce geo-referenced raster swaths. The ADS imagery is subsequently used in the Aerial Triangulation (AT) process in preparation for orthorectification. The horizontal accuracy of the orthorectified imagery is primarily determined by the quality of the airborne GPS, Inertial Measurement Unit (IMU) data and the surface model (digital elevation model or DEM). The AT process is initiated with the population of ADS project files with ABGPS/IMU data, horizontal control from USDA furnished mosaicked DOQQs (mDOQQs) and vertical control picked from the USGS DTED2 DEM data. IMU rotational data is checked by reading common points on the mosaicked DOQQs and on the new imagery. As a final check, stereo models are analyzed for parallax. The absolute orientations for each swath containing exterior orientation parameters for scan line is then output for use in orthorectification. Each DOQQ is inspected for relative horizontal accuracy with adjacent DOQQ tiles. Each DOQQ is inspected for image quality. DOQQs are color and radiometrically balanced over a block consisting of a large number of images. A sample of DOQQs is selected and inspected for relative horizontal accuracy with the USDA furnished mDOQQs. Completed and approved DOQQs are assembled into a countywide MrSID file, using a compression factor of 1:15. |
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