Abstract:

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.

Users should be aware that this is an interim release. The interim compressed county mosaic may contain defects and have horizontal accuracy less than the specified tolerances. Imagery may be replaced to address defects found in a small number of products through quality assurance processes. Imagery containing defects that require the acquisition of new imagery, such as excessive cloud cover, specular reflectance, etc., will not be replaced within a NAIP project year.

This Compressed County Mosaic was generated using MrSID Generation Three (MG3) software using the maximum N-level setting and a target compression ratio of 15:1. All photography was acquired using digital mapping cameras and accompanied by the collection of airborne Global Positioning System (GPS) data. Photography was collected using an Intergraph DMC. image scanners at a resolution of approximately 20 micrometers per pixel. All imagery was collected using Inertial measurement units (IMU) as a means to control the imagery. Orthorectification was performed with custom software and the USGS National Elevation Dataset was used for the elevation model. Digital orthophotos were radiometrically balanced in Intergraph's OrthoPro software. Custom software automatically generated the MrSID project parameter file to control the insertion of the digital orthophotos in the final mosaic. The ordering scheme of the digital orthophotos is based on a last-in-last-on-top scheme.

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