FROM:
Charles W. Challstrom
Acting Director, National Geodetic Survey

SUBJECT:  INSTRUCTIONS: GEORGIA FBN, 1998 (GPS-1273)
Task Numbers:  8K6D2000(FBN/CBN), RK6C0400(ANA)

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 components of the FBN.  This survey will re-observe the 26 FBN stations in Georgia, establish Primary Airport
Control Stations (PACS) at airports in the state in support of the FAA Area Navigation Approach (ANA) project, and replace 12-13 destroyed or blocked Cooperative Base Network (CBN) stations.  NGS will observe the FBN and bench mark ties.  The Georgia Department of Transportation (GADOT), per the cooperative agreement, will observe the CBN ties.

The proposal is to do a combined FBN/ANA/CBN survey in cooperation with GADOT.  NGS agrees to process all data.  GADOT will aid in performing reconnaissance for the FBN and CBN.  GADOT would observe the 12-13 CBNs, while NGS observes all the rest.  NGS will provide reconnaissance assistance to GADOT, if needed.

In addition, a PACS and 2 Secondary Airport Control stations (SACS) must be established at each of 32 additional ANA airports.  Many of the airports have B-order stations at or near them.  (Some are High Accuracy Reference Network (HARN) stations; others were established during obstruction chart airport datum tie projects).  These stations should be checked to see if they meet PACS station requirements.  If they do not, a new PACS must be established and the Georgia contacts and NGS office informed.

GADOT will co-observe with Trimble SSE and SSI receivers, a varying number depending on how many marks need to be replaced in a given area (six to nine receivers available).  Before the project begins, the NGS field party will provide training to the GADOT personnel in the appropriate procedures and specifications
required to perform the survey.  The project will be performed under the technical management of NGS.  NGS will process all observational data in return for GADOT's participation.

In addition, the station at one (1) tide site (Fort Pulaski National Monument, Savannah River) will also be surveyed in this project.  Occupations of this station must meet the FBN specifications for this project.

PURPOSE:

In order to meet America's accelerating positioning and navigation needs, the existing coordinate reference system must be continually renovated and monitored 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.  The FBN fulfills the requirements for this component.  NGS is charged with the Federal responsibility for establishment, observation, monitoring, and maintenance of the FBN.  The FBN provides the critical network foundation for an accurate, consistent, and reliable NSRS.

The NSRS, in turn, provides the common geographic framework for America's spatial data infrastructure.  As such, the 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.

SPECIFICATIONS:

Project requirements for the FBN observations are to ensure 3-centimeter local accuracy in the horizontal component, as well as 3-centimeter local accuracy for the ellipsoid heights.  The CBN will follow the same specifications.

General specifications for the project are as follows.  At each FBN/CBN 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 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.  These same
specifications apply to the CBN.

All FBN observations must be tied to a Continuously Operating Reference Station (CORS) or Central Temporary Continuously Operating Reference Stations (CTCORS).  All stations to be surveyed should be within 150 kilometers of the CORS or one of the CTCORS.  Data from the Atlanta CORS will be used for
observations in the Atlanta area.  Stations to be used as the CTCORS for observations outside of the Atlanta area will be selected by Survey Section A based on security and station spacing.  Contact Field Operations (N/NGS4) for assistance.  Data will be collected at the CTCORS with a full-wavelength, dual-
frequency GPS receiver at a 30 second epoch interval (referenced to the top of the minute).  Data will be collected for a minimum of 72 hours (3 days) while ongoing observations are within the vicinity of each CTCORS, while it is preferable to collect data for a total of 10-15 days at each CTCORS for better positioning.

Duplicate sets of raw GPS data and copies of the observation logs for each CTCORS will be forwarded by the NGS observers to Nancy Doyle, Spatial Reference System Division, daily.  The data should arrive in SRSD no later than 3 days after it was collected.  The CTCORS data will be processed by SRSD using PAGE4 software.  The final CTCORS coordinates derived by SRSD will be provided to Survey Section A for use in the FBN data processing.

In addition to the CORS/CTCORS, if there is another secure site (such as a secure airport) being occupied during ANY of the scheduled 5 1/2 hour observations, continuously collect 24-hour data at that site for as long as the observation schedule permits.  Sites which will be observed continuously for 24 hours or longer may collect data at 30 second epoch interval (referenced to the top of the minute).  The data collected from these additional continuous stations does not need to be
forwarded to SRSD at this time.

In general, station occupation and observing procedures must be carried out according to appropriate sections of the "NGS Operations Handbook," the current Trimble receiver field manuals, and the appropriate field manuals for the Ashtech and Leica dual-frequency receivers.  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, adjustment residuals, and comparison of results with standards external to the project such as Eastern Strain Network measurements.

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 of stations (Table 1) and observing scheme (Table 3) will be provided.

Data Acquisition - Data collection must be accomplished as specified in the Trimble 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 hours apart - 1400 UTC and 1800 UTC.  Each FBN and CBN 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.

Each FBN and CBN (including PACS that are FBNs or CBNs) must be occupied at least three times - twice at one observing window and once at the other observing window.  Each FBN and CBN must be tied to a bench mark in at least two sessions. A different bench mark must be used for each of the two sessions.
PACS that are not FBNs or CBNs only need to be occupied twice. However, each PAC needs both a bench mark tie and a FBN/CBN tie. Bench marks as ties for FBNs, CBNs, and PACS only need to be occupied once.

If FBNs are to be occupied in a session, at least two must be occupied together (i.e., the FBN must be able to "stand on its own.")  Again, the observing scheme shall be arranged to ensure that adjacent FBN and adjacent CBN stations are directly connected in at least one observing session, and at least half of
all FBN and CBN base lines are repeated.

Also, some airports have existing B-order stations that were not suitable as PACS.  If possible, ties should be made between these stations and the PAC at these airports.

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 the FBN and CBN Surveys - Data management, quality review of collected data, and final vector processing for the FBN and CBN surveys 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 IGS ephemerides.  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.  Refer to Chapter 8 of the OMNI 4.0 manual for the latest techniques on fixing integers on medium and
long base lines.

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 A 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 FBN survey will include GPS data from the CORS, CTCORS, FBN, and bench mark stations.  The CORS data should be reduced to the Antenna Reference Point (ARP) rather than the L1 phase center for vector processing.  The FBN survey will be processed and adjusted separately from the PACS/CBN survey.

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.

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 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 facilities 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.

Because of the different types of receivers being used in the project, 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.

DATA COLLECTION INSTRUCTIONS:

The nature of this project requires that all survey data be of the highest possible quality.  All survey equipment shall be tracked by serial number, and inspected and calibrated at the beginning and end of the project.

Carefully monitor the receiver operation and antenna setup during each observing session.  Note any unusual circumstances regarding satellite visibility, receiver operation, weather events, tripod stability, etc., on the observation log.

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.

Carefully field-check the siting, stability, and description of all marks used in this project.  Ensure that full descriptions are written for all marks.

DATA PROCESSING INSTRUCTIONS: PHASE I AND II

The PACS positions determined by previous survey will be spot-checked by processing static vectors between select PACS and nearby Continuously Operating Reference Stations (CORS) or CTCORS.  Notify N/NGS4 of any significant positional discrepancies.

Phase II ANA surveys at airports use the B-order PACS, which were established during Phase I, to locate a minimum of two SACS meeting First-order accuracy standards.  In addition to establishing SACS, the Runway Ends, Displacements, and Stopways and any additional monuments are to be identified and positioned
to meet at least Third-order accuracy standards.  A minimum of one profile in each direction is to be obtained for each Runway that is positioned.  All locations shall be positioned relative to the PACS and must meet the 95% confidence level or the data will be deemed invalid and scheduled for subsequest re-observations.

The static GPS data processing and quality review shall be acomplished using OMNI Version 4.0 software.  Standard processing shall apply observed meteorological data, 30-second epoch intervals, precise ephemerides, and ITRF coordinates to produce fixed-integer or partially fixed-integer ion-free solutions.
Note any processing variatons, data quality problems, and reobservations in the project report.

The kinematic GPS data processing and quality review shall be accomplished using GPSURVEY version 2.3 software.

Success in meeting accuracy standards will be based upon analysis of repeated base lines, loop misclosures, and free-adjustment residuals, and by comparison with prior high-accuracy surveys.

NGS programs COMPGB, OBSCHK, OBSDES, and ADJUST shall be utilized for data quality assurance.

PACS and SACS designations shall be included in the station descriptions.

Data safety backups should be made regularly and kept at physically separate locations.  Raw data shall be archived for at least one year after project completion.

GPS DATA:

Visibility tables and plots of the present satellite constellation for September 16, 1997, 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 "gare028d.609".  All records in connection with this project shall be titled "GEORGIA FBN, 1998".  The project number (accession number) is GPS-1273.

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
                    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
          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
          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
          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 GA data that will be sent to headquarters is:

          Nancy S. Doyle
          Global Positioning System Branch
          Spatial Reference System Division
          N/NGS22
          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 (Bob Siclari)
          Chief, Project Development Branch
          Spatial Reference System Division
           N/NGS21,
          Telephone:  301-713-3194, ext. 111 (ext. 127)
          Fax:  301-713-4316
          e-Mail:  steve@ngs.noaa.gov (bobs@ngs.noaa.gov)

The contacts for the project are:

          M. Greg Johnson
          Georgia Power Company
          Land Department, Bin 20020
          333 Piedmont Avenue
          Atlanta, Georgia   30308
          Telephone:  404-526-4902
          e-mail: greg.johnson@gpc.com

          Lamar Stone
          Georgia Department of Transportation
          Office of Location
          3993 Aviation Circle
          Atlanta, Georgia   30336-1593
          Telephone:  404-699-4470
          e-mail: lamar.stone@dot.state.ga.us

          Luke Cousins, Administrator
          Georgia Office of Intermodal Programs-Aviation
          276 Memorial Drive, SW
          Atlanta, Georgia   30303-3743
          Telephone:  404-651-9200 or 404-651-5209

REPORTS:

A summary of reconnaissance activities shall be included in the final project report.

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/CBN expenses for this project will be charged to task number 8K6D2000.  ANA expenses will be charged to RK6C0400.

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, 1998.

ACKNOWLEDGMENT:

Please acknowledge receipt of these instructions in your Monthly Report.

cc:  N/CS   - F. Maloney
     N/NGS - S. Misenheimer*
     N/NGS1 - G. Mitchell
     N/NGS1X1 - R. Taylor
     N/NGS11 - S. Cofer
     N/NGS2 - J. Till
     N/NGS21 - S. Frakes
     N/NGS21 - R. Anderson
     N/NGS22 - T. Soler
     N/NGS22 - N. Doyle
     N/NGS3 - E. Allen
     N/NGS32 - S. Solbeck*
     N/NGS4 - E. Wade
     N/NGS4 - M. Vorhauer
     N/NGS41 - W. McLemore
     N/NGS41 - J. Blackwell
     N/NGS41 - D. Hoar
     N/NGS41 - J. Olsen
     N/NGS6 - D. Zilkoski
     N/NGS6 - N. Weston
     M. Johnson - Georgia Power Company
     L. Stone - Georgia Department of Transportation
     L. Cousins - Georgia Office of Intermodal Programs
     FGCS Members*

* 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).