1. GENERAL - Geodetic control is required to support mapping of the airports across the United States.

2. DELIVERABLES - Requirements include: reconnaissance reports and survey plans for airports in project areas across the U.S., survey mark recovery notes and descriptions, digital photography of marks, GPS observations, vector processing, GPS adjustment, sketches, visibility diagrams, and reports.

3. RECONNAISSANCE REQUIREMENTS - The Contractor will coordinate with airport officials, recover existing survey marks, select type and location for new marks, and set marks to NGS specifications, write survey mark recovery notes and mark descriptions to NGS specifications, plan a survey network including ties to National Continuously Operating Reference Stations (CORS), the High Accuracy Reference Network (HARN) and bench marks, obtain digital photography of marks, provide mark maintenance (if required), and produce a project sketch and report.

4. MARK SETTING - The Contractor will set stainless-steel rod marks, concrete marks 4 feet deep, and/or disks in drill holes in bedrock. Marks will be set to NGS specifications for type, length, material, stability, and stamping.

5. GPS POSITIONING PROCEDURES - GPS data will be collected using GPS receivers meeting the following criteria: the receiver model must have been evaluated against the Federal Geodetic Control Subcommittee (FGCS) test network, must be a state-of-the-art dual frequency receiver with high quality C/A code or P code pseudo-ranges, must be capable of measuring full wavelength L2 carrier phase, must function acceptably in an Anti-Spoofing environment, and must have a geodetic antenna model that has been calibrated by NGS. The Primary Airport Control Station (PACS) will be tied to the nearest National CORS, HARN station, two bench marks, and two Secondary Airport Control Stations (SACS) by observations ranging from 1.5 to 4 or more hours in length. Extreme care must be taken in tripod set-ups and height measurement. Fixed height tripods should be used.

6. VECTOR PROCESSING - Vector processing will be performed using the latest version of the NGS software package PAGE-NT or equivalent. The 'equivalent' of PAGE-NT is subjective, based on the software's ability to correct for the same systematic errors that PAGE-NT corrects, apply the NGS required antenna offsets, and its ability to reproduce the same results as PAGE-NT. This determination will be made by NGS. NGS precise orbit data and National CORS data will be used.

7. ADJUSTMENT PROCESSING - All airports in a project area should be adjusted together, or the area can be subdivided into groups of airports which are located close together and share tie stations (CORS, BM, HARN). Six adjustments are required: (1) free, (2) constrained with only CORS or CTCORS held, (3) constrained with CORS and HARN stations held, (4) a final free with accuracies, (5) a free vertical holding one bench mark in the center of the project, and (6) a fully constrained vertical (with all approved bench marks held). All data must be submitted in NGS approved formats, and NGS program ADJUST will be used for all adjustments.

8. REPORTING REQUIREMENTS - The Contractor will submit a reconnaissance report prior to setting marks and making GPS observations. The final report will include a project sketch, raw and processed data files, digital recovery notes and description files, observation logs, files from all six adjustments plus other requirements as listed in the Scope of Work.