39910
Calibration Base Lines for Electronic Distance Measuring Instruments (EDMI)
cbl
Data Set
Published / External
37223
ngs
Project
Completed
1974
A calibration base line (CBL) is a precisely measured, straight-line course of approximately 1,400 m used to calibrate Electronic Distance Measuring Instruments (EDMI). A CBL usually consists of four segments ranging from 150 to 1,400 m whose lengths are measured with two high precision EDMI. Since the program began in 1974, NGS has established more than 300 base lines throughout the United States in cooperation with government agencies, universities and professional groups. Participating organizations must select a suitable site that is accessible for public use and install the base line markers 2 to 3 months before measurements are taken. Published CBL distances are available from the National Geodetic Survey, 301-713-3242 or ngs.infocenter@noaa.gov. For more information, please refer to: [1] NOAA Technical Memorandum NOS NGS-8 - Establishment of Calibration Base Lines (1994). [2] NOAA Technical Memorandum NOS NGS-10 - Use of Calibration Base Lines (1977). Both publications are available in pdf from http://www.ngs.noaa.gov/PUBS_LIB/pub_index.html.
CBL's provide surveyors with a means to detect and correct errors in Electronic Distance Measuring Instruments (EDMI). These highly accurate base lines provide a locally accessible standard for length measurement.In addition, NGS makes available the PC program CALIBRAT. This program is used to determine the scale and constant corrections for electronic distance measuring instruments by utilizing measurements taken over previously determined base lines. The formulas used in the program are found in NOAA Technical Memorandum NOS NGS-10, "Use of Calibration Base Lines."
1294
Both mark-to-mark and horizontal distances are published. When the suggested grade specifications are met, it is a simple matter to place the instruments or reflectors at about the same height above the monuments. A direct comparison with the published mark-to-mark data can then be made. Unless steps are taken to set the instruments or reflectors such that the measured distances are in the horizontal plane between monuments, computations are required to compare the observed distances with the published horizontal values.
Theme
ISO 19115 Topic Category
geoscientificInformation
Theme
ISO 19115 Topic Category
location
Theme
NOS Data Explorer Topic Category
Geodetic/Global Positioning
Theme
Calibrations
Theme
Distances
Theme
EDMI
Theme
Geodetic/Global Positioning
Theme
Topographic Data
Theme
oceans
Spatial
U.S. Exclusive Economic Zone
Spatial
United States
National Geodetic Survey
Silver Spring
MD
Data Set
As Needed
document
none
Data Steward
1974
Organization
NGS Communications and Outreach Branch
ngs.infocenter@noaa.gov
(301) 713-3242
(301) 713-4172
Distributor
1974
Organization
NGS Communications and Outreach Branch
ngs.infocenter@noaa.gov
(301) 713-3242
(301) 713-4172
Metadata Contact
1974
Organization
NGS Communications and Outreach Branch
ngs.infocenter@noaa.gov
(301) 713-3242
(301) 713-4172
Point of Contact
1974
Organization
NGS Communications and Outreach Branch
ngs.infocenter@noaa.gov
(301) 713-3242
(301) 713-4172
Publication Date
-175
-67
71
18
Continuing
1974
Unclassified
None
None
http://www.ngs.noaa.gov/CBLINES/calibration.shtml
Downloadable Data
ASCII Text
Text (Unstructured)
http://www.ngs.noaa.gov/CBLINES/calibration.shtml
Online Resource
2012-12-11
Date that the source FGDC record was last modified.
2017-04-05
Converted from FGDC Content Standards for Digital Geospatial Metadata (version FGDC-STD-001-1998) using 'fgdc_to_inport_xml.pl' script. Contact Tyler Christensen (NOS) for details.
2018-02-08
Partial upload of Positional Accuracy fields only.
The accuracy of each distance segment is determined through a least squares adjustment procedure on the assumption the data points were established in a straight line. Accuracies are on the order of 0.1 to 0.3 mm per line segment. Actual accuracies are stated on each individual CBL document.
The coordinates for each CBL are generally scaled from a topo map or positioned using a GPS unit.
The published elevations are for distance reduction purposes only. They are not tied to the the National Vertical Datum. The relative differences between elevations are better than +/-12 mm.
none
none
1
Calibration Base Line monuments are set on a straight line by the requesting organization. After a sufficient time to allow for settling, the base line is measured with two high accuracy short range EDMI on 2 separate days. Observations will be made such that all segments are measured, forward and backward, on each of the 2 days with both instruments. For a 4 monument base line, this will provide a total of 12 distinct observations with each instrument per day. A total of 48 observations during the 2 days will have been taken. Observations are field checked prior to submittal to NGS for adjustment. NGS will check the EDMI before and after each project to insure the observations meet length standards set by the National Bureau of Standards. All observations are then adjusted through a least squares adjustment procedure and thoroughly checked prior to publication.Process Date Range is 1974-present
gov.noaa.nmfs.inport:39910
Tyler Christensen
2017-04-05T13:07:53
SysAdmin InPortAdmin
2023-10-17T16:12:13
2018-02-08
National Geodetic Survey
NGS
1002
Public
No
2018-02-08
1 Year
2019-02-08