NGS EDMI Calibration Baseline (CBL) Program Strategy

1. NGS EDMI Calibration Baseline (CBL) Program Strategy Kendall Fancher FGCS Meeting July, 2008 December 12, 2006

2. What is a NGS Calibration Base Line? A standard NGS base line consists of four monuments set in a straight line with a total length of about 1400 m. 0 m 150 m 430 m 1400 m All combinations of mark to mark distances are measured very precisely using NGS owned calibration EDMI. These equipment are check-calibrated on the Corbin CBL before and after each series of CBL sites are measured and established. This check-calibration serves as the National Institute of Standards and Technology (NIST) connection to the national standard unit of length.

3. What is the work flow associated with establishing/verifying/re-measuring of a CBL? • For a new installation, NGS provides guidelines and survey disks and our customers install the CBL monumentation according to our specifications • NGS check-calibrates the CBL equipment at the Corbin CBL • NGS loans the CBL equipment to our customers • Our customers, if necessary, receive on-site training by NGS personnel in use of the equipment and methodologies • Our customers collect the data sets according to our specifications • NGS check-calibrates the CBL equipment at the Corbin CBL • NGS reviews the resulting data sets and loads the resulting distances and metadata into the CBL database

4. Benefits To Our Partners • CBLs enable the standardization of EDMI to the NIST standard unit of length. • CBLs provide a tool for evaluating the condition and operating precision of EDMI. In other words, the systematic errors associated with a particular EDMI can be determined and corrections applied to subsequent measurements. • In some states it is a legal requirement that surveyors calibrate their EDMI at designated time intervals. NGS CBLs provides a tool to meet this requirement.

5. Instrument Errors Instrument or Additive Constant error - All distances measured with a particular EDMI are subject to constant error. Caused by three factors: • Electrical delays, geometric detours, and eccentricities • Differences between the electronic and mechanical center • Differences between the optical and mechanical center of the reflector

6. Instrument Errors Scale error or the PPM correction- Error induced by a particular EDMI which are linearly proportional to the length of line measured. Can be caused by: • Variations in the modulation frequency of the EDMI • Non-homogenous emission/reception patterns from the emitting and receiving diodes

7. Instrument Errors Cyclic error - Error in a particular EDMI associated with the internal phase measurement caused by unwanted feed through the transmitted signal onto the received signal. Cannot be determined with standard NGS CBL design. Is accounted for or included in the Instrument or Additive Constant error for EDMI with 10 m wavelengths at NGS standard CBLs. Cyclic error is usually sinusoidal in nature with a wavelength equal to the length of the EDMI unit of length.

8. How Many CBLs Are There? 393 Established since 1974 17 Reported as No Longer Usable 11 Reported as Destroyed 365 Active CBLs in the database today

9. Current State of the CBL Program • Data collection software runs on an outmoded operating system requiring hand entry of data • Data analysis software, for verification or re-measurement, is not easily accessible to our customers • Stability of CBLs can only be monitored via regular site visits by NGS • There is no mechanism for monitoring usage of CBLS by our customers • The Corbin CBL, the “Master CBL”, is in danger of becoming unusable because of partial location on military reserve AP Hill and the encroachment of forest.

10. Making the CBL Program “Useful” for our Customers - Acquisition • Modernize the data collection software by upgrading it to run on a Windows platform and interface with EDMI • Allows our customers to run the software on their modern data collectors • Reduces risk of errors created when hand entering data • Allows for the creation of a data file suitable for uploading to an interactive web page

11. Making the CBL Program “Useful” for both Customers and NGS- Analysis • Create an interactive web page for analysis of CBL data for our Customers • Observational data contained within a data file uploaded by our customer is validated and analyzed • Submitted measurements are archived, allowing for ongoing analysis of CBL stability • CBL usage by our customers can be measured

12. Making the CBL Program “Useful” for both Customers and NGS- Design the “Master” CBL • Forced centering piers based upon the PAT 20 monument design • Essential to eliminating set-up errors • Eliminates the need for specialized collimation equipment • Constant Instrument heights are obtained • Monument spacing will accommodate the wavelengths of modern EDMI allowing for the determination of Cyclic error.

13. Making the CBL Program “sustainable” • Reducing financial resources • Training conducted at the Corbin Training Center as opposed to on-site • Customer pays for shipping costs associated with equipment to maintain existing CBL • Reducing personnel resources • Transition from the “old style” to the “Master” baseline • “Master” baselines will serve a larger geographic area and provide the tool for our customers to maintain local “old style” CBLs if desirable

14. Develop and Issue New Guidelines Update NOS NGS 8 – Establishment of Calibration Base Lines February 1994 Update NOS NGS-10 – Use of Calibration Base Lines 1980 Update “NGS EDMI Calibration Base Line Policy” February 9, 1996