Orthophoto Processing: Utilizing all four bands [blue (B), green (G), red (R), and infrared (IR)] digital orthorectification was performed using bilinear interpolation algorithms resulting in a spatial and radiometric transformation of the digital image from line/sample space into NAD 1983 HARN StatePlane New Hampshire FIPS 2800 Feet, Foot US. The interior and exterior orientation parameters from the aerotriangulation process were used to project each pixel into the ground coordinate system, while the ortho grade DEM 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 are tonally balanced to produce a uniform contrast and tone across the entire project. The individual overlapping orthophoto frames were mosaicked together. The ortho photos meet ASPRS horizontal accuracy standards.
Surface Creation: This process involved the development of seamless topographic landform elevation dataset utilizing in-house LiDAR data and data from the National Elevation Dataset to support 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 DEM is suitable for orthophoto production only (not suitable for contour generation). The DEM is used to then generate a Triangulated Irregular Network (TIN) to support orthophoto production.
Imagery Acquisition: Digital aerial imagery was obtained using a UltraCam Eagle camera equipped with Airborne GPS/IMU. A total of 182 flight lines were collected in the spring 2021 and 2022 in multi-spectral (RGB-IR) format. The 0.5 imagery was acquired at an altitude above mean terrain of 10400 feet to yield a pixel resolution suitable for photogrammetric mapping and orthophoto production. The imagery was collected under conditions free from clouds and cloud shadows, smoke, fog, haze, light streaks, snow, ice on water bodies, flooding, excessive soil moisture, and foliage. The imagery consisted of blue, green, red, and infrared bands. Imagery for the photogrammetric mapping and digital orthophotos was captured according to task order specifications regarding, snow, haze, and cloud cover.
Ground Control Point Collection: A total of 122 control points were established throughout the project area 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. Ground control collection followed requirements set forth in the task order specifications. Please see the survey report for more information.
Aerotriangulation: Softcopy aerotriangulation was performed on one large block of imagery. The airborne GPS/IMU data, GPS ground control, and image coordinate measurements were utilized to allow the direct computation of the exterior orientation parameters for each image frame to support the photogrammetric process and orthophoto production.
Created an ArcGIS Mosaic Dataset comprising the original 10,807 GeoTIFF images. The Mosaic Dataset was published as image services in both RGB and CIR color combinations.
Three band orthoimagery is organized in three color bands or channels which represent the red, green, and blue (RGB) portions of the spectrum. Four band orthoimagery is organized in four color bands or channels which represent the red, green, blue (RGB), and near infrared (IR) portions of the spectrum. Each image pixel is assigned a triplet or quadruplet of numeric values, one for each color band. Numeric values range from 0 to 255.