2013 Coastal Georgia 4-Band 8 Bit Imagery

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Softcopy aerotriangulation was performed utilizing the airborne GPS/IMU data, GPS ground control and image coordinate measurements allowing the direct computation of the exterior orientation parameters for each image of the project. | Source Geospatial Form: model | Type of Source Media: CD-ROM

Aerial imagery was acquired using a Zeiss/Intergraph Digital Frame camera (DMC) with a flight design that included a total of 4051 exposures in 64 flight lines. Aerial imagery was supplemented with the simultaneous acquisition of airborne GPS/IMU data, which captured the ground coordinate for the nadir point of each photograph. Aerial imagery was exposed at an altitude of 2400' above mean terrain. | Source Geospatial Form: remote-sensing image | Type of Source Media: external hard drive

Photo Science performed a geodetic control survey in support of a digital orthophoto production project covering the AOI. The survey was done using the Global Positioning System (GPS). A combination of 65 photo identifiable objects and pre-flight targeting was used to provide ground based photo control. Photo control points have a combined local and network accuracy at 95% confidence of less than or equal to five (5) centimeters horizontally and vertically as determined by the residuals of the network adjustment. | Source Geospatial Form: model | Type of Source Media: CD-ROM

A compilation of topographic land form elevation datasets developed through photogrammetric data capture or through the use of existing elevation datasets from various sources for use in developing digital ortho imagery. | Source Geospatial Form: model | Type of Source Media: DVD

Digital aerial imagery was obtained using a large format Z/I Digital Mapping Camera system (DMC) equipped with Airborne GPS/IMU covering the AOI. A total of 169 flight lines with 13859 frames were collected in early 2013 in multi-spectral (RGB and NIR) 16 bits per band format. The imagery was acquired with a 4.7244" (120 m/m) focal length at an altitude above mean terrain of 4800' to yield a raw pixel resolution of 6" suitable for photogrammetric mapping and orthophoto production. The imagery was collected during leaf off conditions in early 2013 under conditions free from clouds and cloud shadows, smoke, fog, haze, light streaks, snow, ice on water bodies, foliage, flooding, and excessive soil moisture. The sun angle threshold was 30 degrees. The imagery consisted of panchromatic, blue, green, red and near infrared bands. The three color bands and near infrared bands have been pan sharpened and archived as frame imagery.

A total of 65 ground based photo control points were established throughout the area of interest using a combination of conventional and GPS survey methods in order to support softcopy aerotriangulation and photogrammetric mapping meeting the accuracies specified in this Scope of Work. This control supplemented the exposure station control obtained from the onboard Airborne Global Positioning System (ABGPS) and Inertial Measurement Unit (IMU). Photo control points established for this project have a combined local and network accuracy at 95% confidence of less than or equal to five (5) centimeters horizontally and vertically as determined by the residuals of the network adjustment.

This process involved the development of seamless topographic landform elevation dataset utilizing a combination of existing public domain elevation data sets existing public domain elevation data sets as well as the stereo compilation of new elevation data from the 2013 stereo imagery using autocorrelation techniques. All elevation data used was capable of supporting the production of digital orthophotography that meet or exceed required orthophoto horizontal accuracy. The topographic features included a grid of elevation points and may include break lines that define ridges, valleys, edge of water, transportation features and abrupt changes in elevation. The final DTM is suitable for orthophoto production only (not suitable for contour generation). The DTM is used to then generate a Triangulated Irregular Network (TIN) to support orthophoto production.

Utilizing all four pan-sharpened bands [blue (B), green (G), red(R) and near infrared (IR)] digital orthorectification was performed using cubic convolution algorithms resulting in a spatial and radiometric transformation of the digital image from line/sample space into State Plane Zone 1002 Georgia West. The interior and exterior orientation parameters were used to project each pixel into the ground coordinate system, while the ortho grade DEM/DTM was used to correct for relief displacement. Radiometric correction software and techniques were used to create orthophoto files that minimize the appearance of image seams and without loss of feature signature. Orthophotos are checked for geometric accuracy, image quality and tonally balanced to produce a uniform contrast and tone across the entire project. The individual overlapping orthophoto frames were mosaicked together and the final tiles were extracted from the image set to a 5,000 x 5,000 foot tiling scheme consisting of 3,346 individual ortho tiles. Delivery included digital ortho photos at a 6" pixel ground sample distance in 8 bit, 4 band (RGB and NIR) uncompressed GeoTIFF and MrSID files. The ortho photos meet a horizontal accuracy of +/- 2.5-feet or less at 95% confidence level when compared to higher accuracy check points based on NSSDA testing standards.