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).