Layer: 2018 Imagery (ID: 0)

Name: 2018 Imagery

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Description: <DIV STYLE="text-align:Left;"><DIV><DIV><P STYLE="margin:0 0 0 0;"><SPAN>Digital imagery was collected at a nominal GSD of 40cm or 50cm using 2 Cessna 441 flying at an average flight height of 8400m AGL for the SH100/SH120 acquisition. Aircraft flew with Leica Geosystem's ADS100/SH120 digital sensors with firmware 4.60. Each sensor collected 12 image bands Red, Green, Blue and Near-infrared at each of three look angles; Backward 19 degrees, Forward 26 degrees and Nadir for the SH100. Backward 10 degrees, Forward 14 degrees, and Nadir for the SH120. The Nadir Green band was collected in high resolution mode effectively doubling the resolution for that band. The ADS100/ADS120 spectral ranges are; Red 619-651nm, Green 525-585nm, Blue 435-495nm and Near-infrared at 808-882nm. The CCD arrays have a pixel size of 5.0 microns in a 20000x1 format at nadir; a 18000x1 format at the backward look angle and a 16000x1 format at the forward look angle. The CCD's have a dynamic range of 72db and the A/D converters have a resolution of 14bits. The ADS is a push-broom sensor the ground footprint of the imagery is approximately 4.8km wide at a nominal 40cm GSD, and 7.2km wide at a nominal 60cm GSD by the length flightline. The maximum flightline length is limited to approximately 100km. The factory calibrations and IMU alignments for each sensor (Serial Numbers: 10540, 10511, 12529) were tested and verified by in-situ test flights before the start of the project. The Leica MissionPro Flight Planning Software is used to develop the flight acquisition plans. Flight acquisition sub blocks are designed first to define the GNSS base station logistics, and to break the project up into manageable acquisition units. The flight acquisition sub blocks are designed based on the specified acquisition season, native UTM zone of the DOQQs, flight line length limitations (to ensure sufficient performance of the IMU solution) as well as air traffic restrictions in the area. Once the sub blocks have been delineated they are brought into MissionPro for flight line design. The design parameters used in MissionPro will be 30% lateral overlap and 40cm or 60cm resolution. The flight lines have been designed with a north/south orientation or east/west where required for efficiency. The design takes into account the latitude of the state, which affects line spacing due to convergence as well as the terrain. SRTM elevation data is used in the MissionPro design to ensure the 40cm or 60cm GSD is achieved over all types of terrain. The raw data was downloaded from the sensors after each flight using Leica XPro software. The imagery was then georeferenced using the 200Hz GPS/INS data creating an exterior orientation for each scan line (x/y/z/o/p/k). Leica Xpro APM software was used to automatically generate tiepoint measurements between the forward, nadir and backward look angles for each line and to tie all flight lines together. The resulting point data and exterior orientation data were used to perform a full bundle adjustment using ORIMA software. Blunders were removed, and additional tie points measured in weak areas to ensure a robust solution. Once the point data was clean and point coverage was acceptable, photo-identifiable GPS-surveyed ground control points were introduced into the block adjustment. The bundle adjustment process produces revised exterior orientation data for the sensor with GPS/INS, datum, and sensor calibration errors modeled and removed. Using the revised exterior orientation from the bundle adjustment, orthorectified image strips were created with Xpro software and the HxIP derived DEM. The Xpro orthorectification software applies an atmospheric-BRDF radiometric correction to the imagery. This correction compensates for atmospheric absorption, solar illumination angle and bi-directional reflectance. The orthorectified strips were then overlaid with each other and the ground control to check accuracy. Once the accuracy of the orthorectified image strips were validated the strips were then imported into Inpho's OrthoVista 7.1.2 package which was used for the final radiometric balance, mosaic, and DOQQ sheet creation. The final DOQQ sheets, with a 300m buffer and a ground pixel resolution of 30cm were then combined and compressed to create the final ortho mosaics.</SPAN></P></DIV></DIV></DIV>

Service Item Id: 7011d8d8944c4d3fa21e9ccb18835b27

Copyright Text: Hexagon, Quantum Spatial, Tahoe Regional Planning Agency

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