1. GENERAL - GPS derived heights are required to improve the network of known elevations across the United States.
2. DELIVERABLES - Requirements include: reconnaissance reports with survey plans for 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 local officials, recover existing survey marks, select type and location for new marks, and set marks to National Geodetic Survey (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) (GPS), 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 project 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 equipment 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 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 quality antenna with ground plane and an antenna model that has been calibrated by NGS. The Contractor must follow guidelines for establishing GPS derived heights (2 to 5 cm) documented in NOAA Technical Memorandum NOS NGS 58 (http://www.ngs.noaa.gov/PUBS_LIB/NGS-58.html). Fixed height tripods shall 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 NGS CORS data will be used.
7. ADJUSTMENT PROCESSING - All stations in a project area should be adjusted together. Four adjustments are required: for each of two levels of the network, each consisting of: (1) free, (2) constrained with all CORS or CTCORS held, (3) constrained with all control stations held, (4) a final free with accuracies. All data must be submitted in NGS approved formats, and NGS program ADJUST will be used for all adjustments. Additional guidelines for GPS derived orthometric height determination will be provided.
8. REPORTING REQUIREMENTS - The Contractor will submit a reconnaissance report prior to setting marks and making GPS observations. Regular status reports will be made via email. The final report will include a project sketch, raw and processed data files, digital recovery notes and description files, observation logs, files from all adjustments plus other requirements as listed in the Scope of Work.