MEMORANDUM FOR: Clifton S. Middleton
Project Director, Survey Section B
FROM: Charles W. Challstrom
Acting Director, National Geodetic Survey
SUBJECT: INSTRUCTIONS: LOUISIANA FBN, 1998 (GPS-1264)
Task Numbers: 8K6D2000(FBN)
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 23 FBN stations in Louisiana. This campaign will be
continuous and will tie into adjoining states. (Some states
will be skipped for seasonal relocations.)
Due to logistical reasons and the fact that the station is
unstable, FBN station SHELL SUBSIDENCE MARK (PID AT1399) has been
dropped from the project.
Stations at three tide sites (South Pass, Grand Isle, and
Cocodrie) will also be surveyed in this project. (The station
at Grand Isle is a FBN station.) (NGS is being reimbursed for
occupying the station at the South Pass tide site.) Occupations
of these stations must meet the FBN specifications for this
project.
Finally, for the Winfield CORS site, reference marks DOYAL
(PID BX1334) and BORO (PID CQ3386) (both CBN's) will be occupied
and tied to the CORS antenna.
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, 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 South Pass, Grand Isle, and Cocodrie tide site surveys will
provide GPS-derived ellipsoid heights, accurate to 3 cm, on tide
site water-level marks along the Gulf coast.
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.
Data from CORS in the region are to be used in the processing.
These CORS include Vicksburg (VIC1), English Turn (ENG1),
Winnfield (WNFL), and Beaumont (BEA5).
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.
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 have
been 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 4 hours
apart - 1500 UTC and 1900 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 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. 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.
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.
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.
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 the 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
units 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:
(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 February 18, 1998, 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
"laro028d.602". All records in connection with this project
shall be titled "LOUISIANA FBN, 1998". The project number
(accession number) is GPS-1264.
LIAISON:
Liaison must be maintained with designated offices at
the National Geodetic Survey headquarters located at:
1315 East-West Highway
Silver Spring, Maryland 20910-3282
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
Questions and problems which could affect the technical adequacy
of the project should be directed to:
Stephen J. Frakes (Douglas 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)
The contact for the project is:
Robert Zurfluh
LADTD
Location and Survey Division
P.O. Box 94245
Baton Rouge, Louisiana 70804
Telephone: 504-379-1134
Fax: 504-379-1850 (or 1860)
Federal Express Address:
1201 Capital Access Road
Room 111
Baton Rouge, Louisiana 70802
For South Pass, Grand Isle, and Cocodrie 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
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. The task number for the station at the South Pass
tide site is 8K6BPT57. (The organization code for South Pass
is NJ4200.)
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.
Attachment
cc: N/CS - F. Maloney
N/CS41 - T. Landon
N/CS42 - J. Oyler
N/NGS - S. Misenheimer*
N/NGS1 - G. Mitchell
N/NGS1x1 - D. Rexrode
N/NGS1x1 - R. Zurfluh
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 - E. Wade
N/NGS4 - M. Vorhauer
N/NGS4 - D. Hoar
N/NGS41 - W. McLemore
N/NGS41 - J. Blackwell
FGCS Members*
Paul Walla, Arkansas Society of Professional Surveyors
Mike White, Arkansas State Highway & Transportation
Department
Frank Howard, Texas Department of Transportation
* 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).