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processing, and storage. The FAA has been under- Airside geographic positioning system (GPS) standably reluctant to accept LIDAR data into the data and landside ground GPS: Data collection Airports Geographic Information System (AGIS) and processing and Third Party Survey System (TPSS) databases the agency uses to support the agency's airport and To collect high-resolution topographic data, aeronautical information-development activities. LIDAR missions typically are flown at low alti- tudes, 1,000 m or lower. The flight path is planned to cover the study area and obtain the desired point SAMPLE SURVEY SPECIFICATION spacing. The flight path includes both parallel FOR AIRBORNE LIDAR and cross flight lines to eliminate shadowing, A primary objective of ACRP Project 03-01 was achieve desirable point density, and support pro- to develop a sample specification that might assist per quality control. Collection aboard the aircraft airport operators and others in procuring obstruction of GPS data using signals from at least four and surveys using LIDAR-based data. While research ideally 12 satellites supports precise timing and conducted by others and work in this project have GPS stamping. A LIDAR survey can generally be suggested that LIDAR technology could become in- completed within 3 to 4 hours of flight time for a creasingly attractive for airport obstruction surveys, typical airport; in contrast to conventional aerial standardization of procedures and formats for data photography, LIDAR flights may be made during collection, processing, and storage is likely to be nighttime. needed to accelerate the technology's adoption. Airport operators or others considering use of The research team found that commercial LIDAR airborne LIDAR-based surveys should ensure that survey contractors have typically incorporated stereo the survey vendor is well qualified and experienced aerial imagery in their LIDAR workflow to enhance with the technology. The research team found that computational efficiency and facilitate accuracy LIDAR-based airport surveys conducted to date have, checks and other quality control and assurance func- for the most part, been conducted without oversight tions. Figure 1 illustrates a typical work process that by NGS or FAA. Data from such surveys may not might be followed for using aerial photography and meet the quality control and quality assurance stan- LIDAR in an airport obstruction survey. A sample dards those agencies seek to maintain to ensure specification, developed by the research team and airspace safety. In the absence of clearly stated included as the appendix to this digest, assumes that specifications and adequate data-quality assurance, stereo imagery will be available to support interpre- the FAA is likely to remain reluctant to accept LIDAR tation of LIDAR data. data into the AGIS and TPSS databases. FAA re- The specification addresses four key aspects of quirements for remote sensing surveys are stated in data acquisition and processing: AC 150/5300-18B. Calibration tests: Radiometric qualification Airport operators or others wishing to use FAA tests for obstruction detection and system cali- funding support to conduct a survey (or to have the bration (factory calibration, field calibration by data produced by the survey be accepted for obstruc- flying over a building site of known topography, tion identification) must meet the requirements of and in-flight calibration) that circular or obtain FAA approval in advance to ex- Survey planning calculations: Grid and point ceed or otherwise deviate from those requirements. spacing (along and perpendicular to the flight The sample specification reflects the characteristics path), field of view, scanner angle and fre- of LIDAR equipment and processes currently in use, quency, ground speed of the aircraft, swath but is designed to be flexible in accommodating higher width, number of flight lines, and line cover- resolution and otherwise more accurate data collec- age perpendicular to the flight line tion methods as industry innovation progresses. The Flight mission planning parameters: Coverage research team concluded that benefits of using LIDAR parameters (to ensure complete coverage of are likely to increase and in some instances may al- the required obstruction identification surface), ready be sufficient to motivate a survey provider and swath overlap, flight line directions, flying airport operator to request this approval. In such a height (as low as possible within the applicable case, the sample specification may be a useful model eye-safety limits), and flight clearance for the survey's design. 4

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LIDAR and Photo Workflow Schematic Client 1. Client Data Requirement, FAA Specifications, Project Deliverables 1.1 Define Project and Products 1.2 Agree on Specs and Budget - Review Appropriate FAA AC 150/5300-17B 1.3 Agree on Schedule 2. Field Operations 2.1 Integrated Survey Control Plan a) Select GPS Base Station Locations b) Predefine ground marks c) Check Points d) Establish control network 2.2 IMAGERY PLAN (Remote Sensing Plan) as per FAA AC 150/5300-17B a) LIDAR b) Photo c) Weather, local coordination d) Approaches/Imagery surfaces 3. Data Acquisition & Processing 4. LIDAR 5. Photo 4.1 Acquisition of Airborne LIDAR data 5.1 Acquisition of aerial photo 5.2 Initialization/calibration of Airborne GPS & IMU 4.2 QC of LIDAR Data on site 5.3 QA/QC for image quality 4.3 GPS Validation Data 5.4 Scan aerial film; submit for approval 4.4 Processing and calibration of LIDAR 5.5 Tie and pass point measurements 4.5 Review and QC field data 5.6 Measure ground control points 4.6 Review LIDAR calibration Boresight values 5.7 Refine aerotriangulation (AT)/bundle adjustment 4.7 Review LIDAR data accuracy testing against 5.8 Submit AT report for approval check points 4.8 Calibrated LIDAR data 5.9 Receive LIDAR products 5.10 Conduct obstruction survey analysis Use Photo & LIDAR data (DEM, Surface model) 4.9 Production of LIDAR output Identify and list obstructions Processing setup Submit for approval Bare earth extraction Bare earth validation Accuracy verification 5.11 Generate ortho using bare-earth DEM 4.10 Generation of deliverable LIDAR products Rectification a) DEM b) Surface Model c) Intensity Image Seam line placement and radiometric 4.11 Delivery balancing 6. Submit Project Deliverables to Client Figure 1 Typical workflow using aerial photo and LIDAR for obstruction survey. (Source: Derived from information provided courtesy of Terrapoint Aerial Services.) 5

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