MEMORANDUM FOR: Clifton S. Middleton Project Director, Survey Section B FROM: Charles W. Challstrom Acting Director, National Geodetic Survey SUBJECT: INSTRUCTIONS: ALABAMA FBN, 1998 (GPS-1250) Task Numbers: 8K6D2000(FBN) 8K6D4000(CORS) GENERAL: The National Geodetic Survey (NGS), in accordance with the NGS Strategic Plan, is engaging in a campaign of observing stations of the Federal Base Network (FBN) to complete the ellipsoidal and orthometric height components of FBN. This survey will observe the 19 FBN stations in Alabama. Bench mark ties for the FBN stations will also be observed. This campaign will be continuous and will proceed into adjoining states. In addition, at the Miller's Ferry Continuously Operating Reference Station (CORS) site, a pair of CORS reference marks is to be tied to both the local FBN/CBN and the CORS antenna. The reference marks are 7-502 and JOSEPHSON. Station 873 5180 TIDAL 1 (PID BH1756) at the Dauphin Island, Mobile Bay, tide site will also be surveyed in this project. (Stations at other tide sites in Mississippi and Louisiana will also be observed as the campaign continues.) Occupations of the station at the tide site must meet the FBN specifications for this project. Lastly, tidal station 872 9840 M (PID BG4867) in Pensacola, Florida, will be tied to in this project. Contact Mr. Ronnie Taylor, Florida Geodetic Advisor, about possibly co-observing. Occupations of this station must meet the FBN specifications for this project. To support software tests that will determine if FBN surveys can be computed along with standard CORS processing, an additional full-wavelength, dual-frequency Global Positioning System (GPS) receiver is needed to act as a Central Temporary CORS (CTCORS) for the northern part of the state. (Existing CORS will be used for the rest of the state.) The receiver shall be deployed at station WALKPORT and shall continuously collect data at a 30-second epoch collection interval during the time that observations are conducted in the northern part of the state. Duplicate sets of raw GPS data and copies of the observation logs for each station will be forwarded by the NGS observers to Nancy Doyle, Spatial Reference System Division, at least every 3 days. PURPOSE: In order to meet America's accelerating positioning and navigation needs, the existing coordinate reference system must be continually enhanced to provide the accessibility and high accuracy required for use with GPS. The digital revolution in mapping, charting, and surveying requires a National Spatial Reference System (NSRS) consisting of, among other components, a network of monumented points having four-dimensional positions. FBN fulfills the requirements for this component. NGS is charged with the Federal responsibility for establishment, observation, monitoring, and maintenance of FBN. FBN provides the critical network foundation for an accurate, consistent, and reliable NSRS. NSRS, in turn, provides the common geographic framework for America's spatial data infrastructure. As such, NSRS serves as the basis for mapping, charting, navigation, boundary determination, property delineation, infrastructure development, resource evaluation surveys, and scientific applications, including crustal motion monitoring, modeling of flooding, storm surge, pollution trajectories, and agricultural runoff. A modernized, accurate, consistent, reliable NSRS is of enormous benefit to state, county, tribal, local, and Federal authorities, as well as to the private sector. The reference marks established at the Miller's Ferry CORS site will provide a very accurate tie to the antenna as an aid to reposition the antenna should that become necessary. The FBN/CBN ties to the CORS marks will also provide site station coordinates relative to the local FBN/CBN, thus reducing the potential for relative error between the stations and the local network. It will also provide a check on FBN/CBN, relative to the CORS coordinates. The Dauphin Island tide site survey will provide GPS-derived ellipsoid heights, accurate to 2 cm, on tide site water level marks along the Gulf coast. SPECIFICATIONS: Project requirements for the FBN observations are to ensure 2-centimeter local accuracy in the horizontal component, as well as 2-centimeter local accuracy for the ellipsoid heights. Data from CORS in the region are to be used in the processing. These CORS include Atlanta CORS L1 Phase Center (ATL1), Miller's Ferry 1 (MLF1), and Mobile Point 1 (MOB1). If possible, the first session of the observations should include a CORS station. General specifications for the project are as follows. At each FBN site, three sessions of 5 1/2 hours duration shall be observed. The observing scheme shall be arranged so that for each station, the start time of one of the observing sessions shall be at least 4 hours different than the other two. The observing scheme shall be arranged to ensure that adjacent FBN stations are directly connected in at least one observing session, and at least half of all base lines are repeated. Specific to the Miller's Ferry CORS project is that for the two reference stations at the site, two sessions of 2 hours each shall be observed. In order to provide a check, the equipment shall be broken down and reset with a minimum of 30 minutes between the two sessions. Since the CORS site must be tied to the nearest FBN/CBN station, FBN station UNION E BASE (PID CN3044) must be occupied simultaneously with the two reference marks. Since UNION E BASE is a FBN station, it needs to be occupied continuously with no break for the full 5 1/2 hour FBN session along with the other stations in the session. In general, station occupation and observing procedures must be carried out according to appropriate sections of the "NGS Operations Handbook," and the current applicable receiver field manuals. Data formats and digital file definitions are given in "Input Formats and Specifications of the National Geodetic Survey Data Base," Volume I. Horizontal Control Data, Federal Geodetic Control Subcommittee, September 1994. Success in meeting the accuracy standards will be based on repeatability of measurements, analysis of loop misclosures, and adjustment residuals. General specifications for the project are given in "Geometric Geodetic Accuracy Standards and Specifications for Using GPS Relative Positioning Techniques," Version 5.0: dated May 11, 1988, reprinted with corrections August 1, 1989. Specific project criteria and deviations from the general specifications are given in the following sections. Project Network - A list (Table 1) and sketch of stations will be provided. Data Acquisition - Data collection must be accomplished as specified in the appropriate dual-frequency receiver field manuals in the compressed mode at a 15-second epoch collection interval. The GPS receivers must be dual-frequency and full- wavelength. Track satellites down to a 10-degree elevation angle. The satellite observing scenario will be provided in Table 2. (Sessions will generally begin at two observing windows 4 1/2 hours apart - 1500 UTC and 1930 UTC. Each FBN must be occupied twice at one time and once at the other.) Vectors between the project stations shall be measured by single sessions consisting of continuously and simultaneously tracking for 5 1/2 hours (except as indicated above for the CORS reference marks). Each FBN must be occupied at least three times - twice at one observing window and once at the other. Each FBN must be tied to a bench mark in at least two sessions. A different bench mark must be used for each of the two ties. Extra bench marks used as ties for FBNs only need to be occupied once. Adjacent FBN stations must be directly connected in at least one observing session, and at least half of all FBN base lines must be repeated. Record weather data just before, immediately after, and at the mid-point of each session. Meteorological data shall also be collected immediately after an obvious weather front passes during a session and immediately before it passes, if possible. Pressure and relative humidity measurements must be made near and at about the height of the GPS antenna phase center. Indicate in the log the location of the barometer and psychrometer. Survey operations shall be conducted with due regard to the safety of personnel and equipment. Contact with the airport traffic control tower is mandatory during surveys at controlled airports. Vector Computations for FBN - Data management, quality review of collected data, and final vector processing for the FBN survey will be accomplished by the field party using OMNI. Vectors shall be computed in the International Terrestrial Reference Frame (ITRF) system, using the most current epoch and precise IGSephemerides. Use 30-second epoch intervals, but 15-second epoch data may be used if it improves ease of data processing. In all cases, integer ambiguities will be fixed, if possible. Refer to Chapter 8 of the OMNI 3.42 manual for the latest techniques on fixing integers on medium and long base lines. Refer to "DRAFT Final Processing Procedures" dated January 1995 for specific information on data processing. The quality of collected data shall be determined from the plots generated from OMNI and by analysis of repeated vectors and free adjustment residuals and/or loop misclosures (most loops consisting of repeated vectors). Survey Section B will perform all quality checks for conformance to NGS format standards, including executing software programs COMPGB, OBSCHK, and OBSDES. The final ITRF vectors will be assessed and transformed to the NAD 83 coordinate system using program ADJUST. The data and results will be submitted to the Observation and Analysis Division. All B-files and G-files must be complete, including *25* and *27* records. Vector Computations for CORS - Data management, quality review, and final vector processing will be accomplished using OMNI. Vectors will be computed in the International Terrestrial Reference Frame (ITRF) 1994, Epoch 1996.0, using precise IGS ephemerides. The GPS data and positions for the CORS antennae are available from NOAA's CORS GPS network. The CORS antenna will be used as the reference station in the OMNI processing for each project. The type of final solution, L1 versus ion-free, will depend on the length of the vectors. For projects in which the vectors from the CORS antenna to the other stations at the site are less than 5 km in length, the final reduction will consist of a L1 fixed solution. For projects which include local FBN/CBN ties, there may be vectors computed from the CORS antenna to the ties which are greater than 5 km in length. These vectors will be computed in a separate processing session from the short (less than 5 km) vectors. In general, vectors greater than 30 km in length are to be computed in an ion-free fixed, or partially-fixed, solution. For vectors between 5-30 km in length, compare both the L1 and ion- free solutions to determine which has the best Post-Fit Residual (PFR) plots. In all cases, integer ambiguities will be fixed for each vector whenever possible. Refer to Chapter 8 of the OMNI 3.42 manual for techniques on fixing integers. The weather data collected at each CORS site shall be averaged, and the average values input into the MERGE program for all stations located at the site. The quality of collected data shall be determined from the plots generated from OMNI and by analysis of repeated vectors and free adjustment residuals and/or loop misclosures. Survey Section B will perform all quality checks for conformance with NGS format standards such as executing software programs COMPGB, OBSCHK, and OBSDES. The final ITRF vectors will be assessed and transformed to the NAD 83 coordinate system using program ADJUST. The NAD 83 (Epoch 1996.0) position for the CORS antennae will be used in the adjustments as the constraint. For the other stations, compare the computed NAD 83 positions to the published NAD 83 positions, if available. The data and results will be submitted to the Observation and Analysis Division. All B-files and G-files must be complete, including *25* and *27* records. Station Descriptions - Station recovery notes must be submitted in computer-readable form using DDPROC software. Include the name, address, and telephone number of a property owner or other contact. Special Requirements - Coordination must be maintained with the following people who are involved in the project: (1) Mr. Don Spillars, Alabama Department of Transportation, who is the contact for this project, (2) Mr. Jeffrey Oyler, who can supply Dauphin Island tide site information, (3) Messrs. Paul Delucas, Mike Scroggins, Marty Chavers, and Jay Shelley, who are the points-of-contact for the Miller's Ferry CORS site, and (4) Mr. Ronnie Taylor, Florida Geodetic Advisor, who can possibly co-observe station 872 9840 M in Pensacola, Florida. Antenna set-up is critical to the success of this project. Fixed-height tripods are required for all receivers. The plumbing bubbles on the antenna pole of the fixed-height tripod must be shaded when plumbing is performed. They must be shaded for at least 3 minutes before checking and/or re-plumbing. Also, the perpendicularity of the poles must be checked at the beginning of the project and any other time there is suspicion of a problem. A rubbing of the stamping of the mark must be made at each visit to a station. If it is impossible to make a rubbing of the mark, a plan sketch of the mark must be substituted, accurately recording all markings. In addition, a layout sketch of the CORS facility should be made. Include the location of the marks, antenna, buildings, and any other identifying characteristics of the area on the sketch, as well as the approximate height of the CORS antenna. For each station visited, a visibility obstruction diagram must be prepared and the TO-REACH description carefully checked for errors or omissions. The following must be recorded at each occupation of a station: (1) receiver manufacturer, (2) antenna manufacturer, (3) receiver model number (part number), (4) antenna model number (part number), (5) the complete serial number of the receiver, and (6) the complete serial number of the antenna. Success of this project requires that the highest quality GPS data be collected. Therefore, during each station occupation, the operators shall carefully monitor the operation of the receivers. Any irregularities in the data due to equipment malfunction, DOD adjustment of the satellite orbit, obstructions, etc., must be reported to the Field Operations Branch, N/NGS41, as soon as possible and noted on the observing log. If the quality of observations for an observing session is questionable, notify the Field Operations Branch immediately. The survey team shall not depart the project area until they have quality reviewed all data, advised N/NGS21, and notified N/NGS41. GPS DATA: Visibility tables and plots of the present satellite constellation for January 5, 1998, will be provided. For operational use, current data must be generated with Trimble mission planning software or from program SATMAP. Project report and data listed in Annex L of "Input Formats and Specifications of the NGS Data Base" and in the attached addendum for the adjustment portion must be transmitted. Any data considered suspect as to quality in achieving accuracy standards should be sent via FedEx immediately for office review. Backup of transmitted data must be held until notified by the Field Operations Branch, N/NGS41. The data set collected during the project shall be named "alro028d.586". All records in connection with this project shall be titled "ALABAMA FBN, 1998". The project number (accession number) is GPS-1250. LIAISON: Liaison must be maintained with designated offices at the National Geodetic Survey headquarters located at: 1315 East-West Highway Silver Spring, Maryland 20910 Questions and problems concerning survey field operations should be directed to: William T. McLemore, Jr. Chief, Field Operations Branch Observation and Analysis Division N/NGS41, SSMC III, Station 8564 Telephone: 301-713-3215, ext. 117 Fax: 301-713-4327 e-Mail: mclemore@ngs.noaa.gov Questions and problems concerning adjustment processing should be directed to: Maralyn L. Vorhauer Observation and Analysis Division N/NGS4, SSMC III, Station 8562 Telephone: 301-713-3176, ext. 104 Fax: 301-713-4327 e-Mail: maralyn@ngs.noaa.gov Questions and problems concerning vector processing should be directed to: Juliana Blackwell Field Operations Branch Observation and Analysis Division N/NGS41, SSMC III, Station 8458 Telephone: 301-713-3215, ext. 108 Fax: 301-713-4327 e-Mail: juliana@ngs.noaa.gov Questions and problems concerning using CORS data in processing should be directed to: Neil Weston Spatial Reference System Division N/NGS2, SSMC III, Station 8622 Telephone: 301-713-3169, ext. 146 Fax: 301-713-4315 e-Mail: nweston@ngs.noaa.gov The contact point for the duplicate set of NGS data that will be sent to headquarters is: Nancy S. Doyle Global Positioning System Branch Spatial Reference System Division N/NGS22, SSMC III, Station 8137 Telephone: 301-713-3208, ext. 159 Fax: 301-713-4324 e-Mail: nancy@ngs.noaa.gov Questions and problems which could affect the technical adequacy of the project should be directed to: Stephen J. Frakes (Doug Hendrickson) Chief, Project Development Branch Spatial Reference System Division N/NGS21, SSMC III, Station 8853 Telephone: 301-713-3194, ext. 111 (ext. 127) Fax: 301-713-4316 e-Mail: steve@ngs.noaa.gov (dough@ngs.noaa.gov) Coordination must be maintained with the following: Mr. Don Spillars Alabama Department of Transportation 1409 Coliseum Boulevard Montgomery, Alabama 36130-3050 Telephone: 334-242-6614 Mr. Ronnie L. Taylor NOS Advisory, Florida c/o FLDEP, Bureau of Survey and Mapping Mail Stop 105 3900 Commonwealth Boulevard Tallahassee, Florida 32399 Telephone: 850-488-2427 Fax: 850-413-9001 e-Mail: taylor_RO@NGW.dep.state.fl.us Federal Express Address: c/o Bureau of Survey and Mapping Capital Center Outlet, C1, Rm 233 5050 west Tennessee St. Tallahassee, Florida 32304 For Dauphin Island tide site information, contact: Jeff Oyler NOAA, Atlantic Operations Section 808 Principal Court Chesapeake, Virginia 23320-3639 Telephone: 757-436-0200 e-Mail: oyler@fob.noaa.gov Contact the Points-of-Contact 3 or 4 days before arriving at the Miller's Ferry CORS site. The Points-of-Contact are: Paul Delucas/Mike Scroggins/Marty Chavers/Jay Shelley Millers Ferry Project 1606 Powerhouse Road Camden, Alabama 36727 Telephone: 334-682-4655 Fax: 334-682-9060 Names and telephone numbers of local contacts are given in the station description material. ADDRESS: Keep N/NGS41 informed of the party's post office, physical address, and telephone number at all times. PUBLICITY: See "NGS Operations Handbook," Section 1.4.1. EXPENSES: FBN expenses for this project will be charged to task number 8K6D2000. CORS expenses will be charged to 8K6D4000. TRAVEL: Travel and per diem are authorized in accordance with Federal Travel Regulations, Part 301-7, Per Diem Allowances. Current per diem rates were effective January 1, 1997. ACKNOWLEDGMENT: Please acknowledge receipt of these instructions in your Monthly Report. cc: N/CS - F. Maloney N/NGS - S. Misenheimer* N/NGS - W. Strange N/NGS1 - G. Mitchell N/NGS1X1 - R. Taylor N/NGS1X1 - D. Rexrode N/NGS11 - S. Cofer N/NGS2 - J. Till N/NGS2 - N. Weston* N/NGS2 - D. Zilkoski* N/NGS21 - S. Frakes N/NGS21 - R. Anderson N/NGS21 - D. Hendrickson* N/NGS22 - T. Soler N/NGS22 - N. Doyle N/NGS3 - E. Allen N/NGS4 - D. Hoar N/NGS4 - M. Vorhauer N/NGS4 - E. Wade N/NGS41 - W. McLemore N/NGS41 - J. Blackwell AMC - J. Albright* FGCS Members* James Zeigler, Tennessee Department of Transportation* Don Spillars, Alabama Department of Transportation* Ray Bass, Alabama Department of Transportation* Paul Delucas, Miller's Ferry Project M. Greg Johnson, Georgia Power Company Lamar Stone, Georgia Department of Transportation NOS, NOAA - J. Oyler N/OES21 - Tom Landon * first page only DATA TO BE SENT TO HEADQUARTERS RELATING TO THE ADJUSTMENT PORTION OF THE PROJECT Note that all except specified files or listings can be paper printouts or ASCII files on disk; be sure to keep backups until notified that the data base is loaded. Free adjustment. [For A- and B-order projects, the data are not scaled. First- order projects would also have a free adjustment using the modified G-file.] Constrained horizontal adjustment holding previously published A- and B-order stations and ellipsoid heights (optional). Constrained vertical adjustment holding NAVD 88 heights. Final combined Blue Book file (ASCII required). Free adjustment with accuracies. Accuracy listing (output of BBACCUR). (Paper required). ELLACC output. OBSCHK output*. CHKDESC output*. OBSDES output*. *any errors or warning messages must be explained. Copies of data used to determine fixed control, both horizontal and vertical. Final description file (ASCII required). Final G file (ASCII required).