MEMORANDUM FOR: Clifton S. Middleton
Project Director, Survey Section B
FROM: Charles W. Challstrom
Acting Director, National Geodetic Survey
SUBJECT: INSTRUCTIONS: OREGON FBN, 1998 (GPS-1333)
Task Numbers: 8K6D2000 (FBN)
8K6D4000 (CORS FBN TIE)
8K6D5000 (HEIGHT MODERNIZATION)
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 73 FBN stations in Oregon. This campaign will be
continuous and will tie into adjoining states. (Some states will
be skipped for seasonal relocations.)
Stations at four tide sites along the Pacific Ocean coast will
also be surveyed in this project. Occupations of these stations
must meet the FBN specifications for this project (height
modernization).
In addition, at the Cape Blanco CORS site, a pair of CORS
reference marks is to be tied to both the local FBN and the CORS
antenna. The names of the reference marks are CAB1 A (PID
AF8757) and CAB1 B (PID AF8756).
To support software tests, a full-wavelength, dual-frequency
Global Positioning System (GPS) receiver is needed to act as a
Central Temporary Continuously Operating Reference Station
(CTCORS) where there are no existing CORS within 150 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 72 hours or more,
before being relocated.
Mr. Curtis Smith, the Oregon State Advisor, is coordinating the
co-observing by various organizations of approximately 74
additional Cooperative Base Network (CBN) stations that are also
to meet the FBN specifications for this project. In exchange for
Oregon organizations occupying approximately one-third of the FBN
stations, NGS will perform all data processing. 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.
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 tide site (height modernization) surveys will provide GPS-
derived ellipsoid heights, accurate to 3 cm, on tide site water-
level marks along the Pacific coast.
The reference marks established at the Cape Blanco CORS site will
provide a very accurate tie to the antennae as an aid to
reposition the antennae should that become necessary. The FBN
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 stations and the local network. It
will also provide a check on FBN/CBN, relative to the CORS
coordinates.
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.
The names of the CORS sites to be used will be provided.
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 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 Cape Blanco CORS site 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 BLCO (PID OA1625) must
be occupied simultaneously with the two reference marks. Since
BLCO is an 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 preliminary list (Table 1) and sketch of
stations have been provided. A final list and sketch will be
provided as soon as possible.
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 - 1540 UTC and 1945 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 PAGE4. 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 for data
processing. Antenna reference point (ARP) positions will be used
for the CORS. 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 Cape Blanco 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 PAGE4, by analysis of repeated vectors and/or
comparison of station positions, 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 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:
(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 August 13, 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
"orro088d.660". All records in connection with this project
shall be titled "OREGON FBN, 1998". The project number
(accession number) is GPS-1333.
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
Geosciences Research Division
N/NGS6, SSMC III, Station 9830
Telephone: 301-713-2847, ext. 202
Fax: 301-713-4475
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:
Curtis L. Smith
National Geodetic Survey
P.O. Box 12114
Salem, Oregon 97309
Telephone: 503-378-5458
Fax: 503-986-3548
Federal Express Address:
Curtis L. Smith
Oregon Department of Transportation
300 E. Summer Street
26 Transportation Bldg.
Salem, Oregon 97310
For tide site information, contact:
Brooks Widder
Oceanographic Products and Services Division
Requirements and Engineering Branch, N/CS41
SSMC4/Station 6342
1305 East-West Highway
Silver Spring, Maryland 20910-3282
Telephone: 301-713-2902, ext. 184
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. Expenses for the CORS FBN tie will be charged to
task number 8K6D4000. Expenses for the tide sites (height
modernization) will be charged to task number 8K6D5000.
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 - N. Prahl
N/CS41 - B. Widder
N/NGS - S. Misenheimer*
N/NGS1 - G. Mitchell
N/NGS1x1 - J.D. D'Onofrio
N/NGS1x1 - G. Perasso
N/NGS1x1 - C. Smith
N/NGS11 - S. Cofer
N/NGS2 - J. Till
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*
Bernard Kelly, Idaho Transportation Department
Brett Lane, Clark County, Nevada
* 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).