FROM: Charles W. Challstrom
Acting Director, National Geodetic Survey
SUBJECT: INSTRUCTIONS: NEW MEXICO FBN, 1999 (GPS-1381)
Task Numbers: 8K6D2000 (FBN), 8K6D4000 (CORS FBN/CBN TIE)
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 the FBN. This survey will observe the 35 FBN stations in New Mexico. This campaign will be continuous and will tie into adjoining states. (Some states will be skipped for seasonal relocations.)
In addition, five bench marks have been added to the project as bench mark ties, and station NM BASE 1 will be surveyed, although it is being dropped as an FBN station.
In addition, at the Tucumcari 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 TCUN A and TCUN B, and the FBN/CBN tie station to use is CARI 3 (PID FM0999). (The backup tie station is FT SUMNERAIR [PID EP0641].)
A full-wavelength, dual-frequency Global Positioning System (GPS) receiver is needed to act as a Central Temporary CORS (CTCORS) where there are no existing CORS within 300 km of the ongoing observations. The receiver shall be deployed at a relatively secure station within the vicinity of the ongoing observing sessions. The receiver shall continuously collect data at a 30-second epoch collection interval for a minimum of 72 hours and for as long as observations are ongoing in the vicinity of the
CTCORS. (Even if there is an existing CORS within 300 km of the ongoing observations, deploy a receiver at a relatively secure station and collect data for 72 hours or more.)
Mr. William Stone, the NGS Advisor to New Mexico, is coordinating the co-observing by various organizations of approximately 25 additional Cooperative Base Network (CBN) stations that are also to meet the FBN specifications for this project. The project will be performed under the technical management of NGS.
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. 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, 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.
The reference marks established at the Scottsdale 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 tie 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 reference marks and the local network. It will also provide a check on the FBN/CBN, relative to the CORS coordinates.
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 the CORS in the region are to be used in the processing. The following is a list of the CORS that should be used: TUCUMCARI (tcun), PIETOWN (pie1), and WHITE SANDS (wsmn). Positions and data are available from the NGS web site.
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 from 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 Tucumcari CORS site is that for the two reference marks 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, the FBN/CBN tie station CARI 3 (PID FM0999) (or backup station FT SUMNERAIR [PID EP0641]) must be occupied simultaneously with the two reference marks. (Since stations CARI 3 and FT SUMNERAIR are both part of the project, they are to be occupied for the entire 5 1/2 hour session with no equipment breakdown.)
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, revised and reprinted November 1998. 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 involved in this project 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 has been provided in Table 2. (Sessions will generally begin at two observing windows at least 4 hours apart - 1600 UTC and 2005 UTC. Vectors between the project stations shall be measured by single sessions consisting of continuously and simultaneously tracking for 5 1/2 hours.
Each FBN station must be occupied at least three times - twice at one observing window and once at the other. Each FBN station 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.
Adjacent FBN stations must be directly connected in at least one observing session, and at least one-half of all FBN base lines must be repeated. The CORS base lines will be repeated. CORS and CTCORS data will be used throughout the project.
For this project, each CBN station must also be occupied three times as described above. However, CBN stations can be tied to adjacent FBN stations (if the FBN station is closer than a CBN station), and a base line consisting of a CBN station and a FBN station can be used in the repeated-base line requirement mentioned above for the CBN portion of this project.
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 any controlled airports.
Vector Computations - Data management, quality review of collected data, and final vector processing for the FBN survey will be accomplished by the field party using PAGES. 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 for data processing.
Monument positions will be used for CORS when available, otherwise, antenna reference point (ARP) positions will be used. For stations where weather data are not available, or are suspect, predicted values computed based on the station's latitude, height above mean sea level, and time and day of year will be used. Use 15 degrees as the cutoff elevation angle in data processing. A cutoff angle of 10 degrees may be used when necessary to improve results.
The type of final solution, L1 versus ion-free, will depend on the length of the vectors. For vectors which are less than 10 km in length, the final reduction will consist of a L1 fixed solution. These vectors will be computed in a separate processing session from the longer vectors computed in an ion-free solution.
In general, vectors greater than 10 km in length are to be computed in an ion-free fixed, or partially-fixed, solution. In all cases, integer ambiguities will be fixed for each vector whenever possible.
For the Tucumcari CORS reference marks, the CORS antenna at the site will be used as the reference station in the data processing.
The quality of collected data shall be determined from the plots generated from PAGES, by analysis of repeated vectors and/or comparison of station positions, and free adjustment residuals and/or loop misclosures. In addition, a constrained adjustment constraining all CORS will be performed.
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 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 - Antenna set-up is critical to the success of this project. Fixed-height tripods are preferred 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.
When a fixed-height tripod is not used, the height of the antenna must be carefully measured to prevent station set-up blunders from occurring. Tribrachs used for these set-ups must be checked and adjusted when necessary. Totally independent measurements of the antenna height above the mark in both metric and English units must be made before and after each session. Someone other than the observer must check the measurement computations by carefully comparing measurements and then entering his/her initials on the log.
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.
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:
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 March 8, 1999, have been reviewed and two observing windows selected. 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 "nmro039d.694". All records in connection with this project shall be titled "NEW MEXICO FBN, 1999". The project number (accession number) is GPS-1381.
LIAISON:
Liaison must be maintained with designated offices at the National Geodetic Survey headquarters located at:
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. Expenses for the CORS FBN/CBN tie will be charged to task number 8K6D4000.
TRAVEL:
Travel and per diem are authorized in accordance with Federal Travel Regulations, Part 301-11, Per Diem Expenses, and Appendix A to Chapter 301. Current per diem rates were effective January 1, 1999.
ACKNOWLEDGMENT:
Please acknowledge receipt of these instructions in your Monthly Report.
Attachment
cc: N/CS - D. MacFarland
N/NGS - D. Zilkoski*
N/NGS - S. Misenheimer*
N/NGS1 - G. Mitchell
N/NGS1x1 - D. Minkel
N/NGS1x1 - R. Cohen
N/NGS1x1 - W. Stone
N/NGS11 - S. Cofer
N/NGS21 - S. Frakes
N/NGS21 - R. Anderson
N/NGS21 - D. Hendrickson*
N/NGS22 - T. Soler
N/NGS3 - E. Allen
N/NGS4 - E. Wade
N/NGS4 - M. Vorhauer
N/NGS4 - D. Hoar
N/NGS41 - W. McLemore
N/NGS41 - J. Blackwell
N/NGS5 - R. Snay
N/NGS6 - D. Zilkoski*
N/NGS6 - N. Weston
FGCS Members*
Phil Tuwaletstiwa, Hopi Tribe
Lemont Yazzie, Navajo Land Department
Clara Walker, Cochise County Highway Floodplain
Dennis Goreham, Utah Automated Reference Center
Frank Howard, Texas Department of Transportation
Gerald Middleton, Oklahoma Department of Transportation
Garry Nielsen, NM State Highway and Transportation Department
Rick Fencl, NM State Highway and Transportation Department
Jim Reilly, New Mexico State University
Jay Innes, Bureau of Land Management
Jan Fiala, City of Albuquerque/Public Works Department
Jim McNees, Office of the State Engineer
Garland Burnett, Santa Fe National Forest
Darrell Herrera, Los Alamos National Laboratories
Gilbert Chavez, City of Las Cruces
David Worley, City of Rio Rancho
Craig Gillio, Taos Surveying
Jim Botsford, Botsford Land Surveying, Inc.
Rusty Elliott, Wilson and Company
Tom Ketcheson, Indian Health Service
Erle Wright, Santa Fe County
Ed Pinson, National Imagery and Mapping Agency
Steve Harder, University of Texas at El Paso
* 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.]
Copies of data used to determine fixed control, both horizontal and vertical.
Final description file (ASCII required).
Final G file (ASCII required).