UNITED STATES DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
NATIONAL OCEAN SERVICE
National Geodetic Survey
Silver Spring, Maryland 20910-3282
Feb 9, 1996
MEMORANDUM FOR: Distribution
FROM: Captain Lewis A. Lapine NOAA
Director, National Geodetic Survey
SUBJECT: NGS EDMI CALIBRATION BASE LINE POLICY
l. A standard Calibration Base Line (CBL) will consist of four
monuments, set at 0 and approximately 150, 400-430, and
1,000-1,400 meters and be established according to the
specifications developed by the National Geodetic Survey
(NGS), titled "Establishment of Calibration Base Lines,"
NOAA Technical Memorandum NOS NGS 8, Revised June 1982.
NGS will provide a 100-foot tape verification section on a
CBL, using Electronic Distance Measuring Instruments (EDMI),
if requested by participants.
NGS will no longer tape the section between the 0-meter
monument and the approximate 150-meter monument. Instead,
NGS will measure this section with a more rigorous use of
EDMI and computer validation software. Consistently high
relative accuracy obtained from the CBL EDMI and improved
measurement-procedures have made NGS' use of IMVAR tapes in
the CBL obsolete.
The NGS calibration EDMI is check-calibrated on the NGS
Instrumentation and Methodologies (I&M) Branch base line,
located at Corbin, Virginia, before and after each series
of CBL sites are measured and established. This check-
calibration will serve as the National Institute of
Standards and Technology connection to the national
standard.
2. There are two ways NGS will assist in establishing CBLs:
(a) NGS will loan CBL equipment to a state or local
governmental agency which has demonstrated expertise in
establishing CBL sites or to an agency using the assistance
of an NGS state advisor. The "demonstrated expertise" can
only be gained through special training received from the
I&M Branch facility.
The exact number and location of the CBL sites will be
agreed upon prior to the loan. The loan will be limited to
15 days. Validation of the CBL sites will be dependent on
the calibration check performed on the I&M Branch CBL. The
fee for this loan arrangement will be $500 plus shipping.
The fee will cover the cost of the pre- and post-calibration
checks, equipment maintenance, data adjustment, and
providing the results to participants. The governmental
agency is responsible for any damage to the equipment while
on loan.
(b) NGS will measure a CBL using one NGS headquarters
employee for a $2,500 fee. Help from the state or local
governmental agency is required. This fee includes
measuring a standard four-monument CBL in the conterminous
United States, adjusting the data, and providing the results
to participants. If an EDMI 100-foot tape verification
section is requested on a CBL, there will be an additional
charge of $250.
If NGS is requested to measure a base line that deviates
from the standard four-monument configuration, NGS will
require an additional $500 reimbursement for each additional
monument requiring use of EDMI.
3. NGS will not establish a new CBL less than 75-highway miles
from an existing one under normal conditions. However,
under special conditions, e . g., in metropolitan areas, CBL
sites spaced less than 75-highway miles may be considered.
CBL measurements will be scheduled to minimize NGS travel
expenses. A minimum of three CBL sites must be requested by
one or more participants in a state (or nearby area) before
NGS will schedule personnel to travel to that area to
perform measurements. If such an arrangement is not
possible or would cause an unreasonably long delay, NGS will
attempt to accommodate these requests en route to other CBL
sites. The cost for the CBL may be increased to accommodate
additional travel expenses.
4. Participants are required to monument the CBL at least
4 months prior to measurements and, where appropriate,
include one freeze/thaw cycle before the measurements are
made. If requested, NGS will provide the surface disks to
the participants.
NGS will provide one complimentary copy of "Use of
Calibration Base Lines," NOAA Technical Memorandum
NOS NGS-10, Reprinted with Corrections, 1980; and
"Establishment of Calibration Base Lines," ‚NOAA Technical
Memorandum NOS/NGS 8, Revised June 1982, to participants.
5. Two weeks prior to shipment of equipment or arrival of the
NGS employee, participants will clear the CBL site of all
interfering grass, shrubs, debris, etc., and perform third-
order, double-run, differential leveling over the monuments.
6. For NGS measurement operations, only one NGS employee will
come to the CBL site. Participants are required to provide
two local experienced instrument personnel to assist NGS
with the measurements.
In addition, participants are required to execute a
cooperative agreement with the NGS I&M Branch and provide a
map or diagram showing the CBL layout and location.
7. Participants, and future CBL users, are responsible for
obtaining whatever liability insurance coverage is required
by the property owner.
8. The NGS Spatial Reference System Division (SRSD) is
responsible for quality control and final computation and
analysis of CBL measurements. SRSD will also maintain
automated measurement records, including those submitted to
NGS by local users, and analyze these data for CBL
stability.
9. The NGS Geodetic Services Division (GSD) is responsible for
the publication of CBL results and for maintaining the
automated publication records. GSD will also maintain a
list of active local CBL‚ contacts, including addresses and
telephone numbers.
10. NGS will adjust and publish appropriate CBL measurements
made by others. The measurements must be made in accordance
with NGS specifications and must be adjustable with
satisfactory results. The observations must be submitted in
the NGS-prescribed, computer-readable format.
Further information regarding the CBL program is available from the
NGS I&M Branch, Telephone: 540-373-1243, Fax: 540-373-4327;
E-mail
Adopted: NGS Executive Steering Committee, January 31, 1996
Contact information updated: March, 1999
Distribution:
N/NGS - Challstrom N/NGS - Leigh
N/NGS - Quinn N/NGSl - Mitchell
N/NGS - Lucas N/NGS2 - McKay
N/NGS - Spencer N/NGS3 - Floyd
N/NGS - Strange N/NGS4 - Wade
N/NGS - Weston N/NGS5 - Schwarz -
N/NGS - Fisher NCGS - Gary Thompson
ACSM - John Lisack NSPS - James Granger