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by David Conner Geodetic Advisor to the State of Ohio National Geodetic Survey, NOAA

by David Conner Geodetic Advisor to the State of Ohio National Geodetic Survey, NOAA Dave.Conner@noaa.gov. International Great Lakes Datum Overview Presented at a Height Modernization Program meeting January 9, 2014. NGS and the NSRS Who are those guys? And what is CO-OPS?.

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by David Conner Geodetic Advisor to the State of Ohio National Geodetic Survey, NOAA

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  1. by David Conner Geodetic Advisor to the State of Ohio National Geodetic Survey, NOAA Dave.Conner@noaa.gov International Great Lakes DatumOverviewPresented at a Height Modernization Program meetingJanuary 9, 2014

  2. NGS and the NSRSWho are those guys? And what is CO-OPS? • NOAA's National Geodetic Survey (NGS) defines and manages a National coordinate system which includes NAVD88 and NAD83. This network, the National Spatial Reference System (NSRS), provides the foundation for transportation and communication; mapping and charting; and a multitude of scientific and engineering applications. • NGS was known as the US Coast and Geodetic Survey (USC&GS) until 1970 when it was renamed to become part of the newly formed National Oceanic and Atmospheric Administration (NOAA). NOAA is within the US Dept of Commerce. NGS is within NOAA’s National Ocean Service (NOS). • NOS’s Center for Operational Oceanographic Products and Services (CO-OPS) is responsible for monitoring tides, water levels and currents. They maintain a network of 53 water level gauges throughout the Great Lakes and their connecting channels. They are responsible for determining heights associated with the International Great Lakes Datum (IGLD), which they do in cooperation with NGS and our International partners in Canada.

  3. IGLD … what is it? The IGLD is a dynamic height system. Dynamic heights, by definition, define a water level surface. They are the base height system used for IGLD 1985 in the Great Lakes. Dynamic heights are the reference system of choice for large hydraulic systems everywhere. NAVD 88 heights are typically given as orthometric heights, although they can also be expressed as dynamic heights. Orthometric heights generally do not define a water level surface. IGLD heights are corrected NAVD 88 dynamic heights. Hydraulic correctors (HC) are applied to NAVD 88 dynamic heights to make them consistent with observed water levels on the Great Lakes. HC’s are the difference in the mean water level for the reference period 1982 -88 (7 year) between a subordinate gauge and the primary gauge on a lake. Hydraulic correctors are typically less than a few cm but can exceed 10 cm (- 10.0 cm on Lake Superior, + 11.4 cm on Lake Michigan).

  4. IGLD … “I” is for International! Management of these waters is governed by International Treaty administered by the International Joint Commission The Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data meets twice each year and recently held its 95th meeting. It is made up of US and Canadian scientific agency representatives. Published water level data are coordinated by government agencies in both countries to ensure there is agreement. Coordinated basic hydraulic and hydrologic data are required to solve numerous international problems related to joint use of International waters

  5. IGLD … Why is it important? The Great Lakes are a vast hydraulic system with water levels and flows influenced by engineered channels and control structures. The entire region is tilting due to post-glacial rebound (aka glacial isostatic adjustment … GIA) The absolute rate of change at a given location must be considered along with the relative rate of change across the region. The Great Lakes basin is tilting at a rate of about 60 cm (~ two feet) per century.

  6. National Spatial Reference System (NSRS) Cleveland Water Level Gauge and GPS CORS The leveling network and water level observation network intersect at the gauges, increasingly co-located with GNSS CORS U.S. = 53 gauges, 13 with CORS Canada = 33 gauges, 9 with CORS

  7. Vertical rate of change due to Post-Glacial Rebound International Great Lakes Datum of 1985 (IGLD 1985), IGLD 2020 is coming

  8. IGLD … Why is it useful? It is a dynamic height system which can be used to relate various data to a common water level surface It provides a mechanism for the US and Canada to reference heights to a common datum throughout the Great Lakes region Each country has adopted other vertical datums for general use. - The US vertical datum is NAVD 88. - The Canadian vertical datum was CGVD 28 until it adopted CGVD 2013 in November 2013

  9. IGLD … When/where is it used? It is used for basic hydraulic and hydrologic data related to engineering and scientific works on or near Great Lakes waters in both the US and Canada These works include things related to navigation and management of water … charts, dredging, erosion, marine boundary determination, bridges, locks, dams, sewage and drainages systems, nuclear power plant water intakes and much more.

  10. IGLD … Why is there more than one? The IGLD is revised about every 30 years to remove the effect of GIA from published heights. IGLD 1985 is the current datum. It was preceded by IGLD 1955, USLS 1935, USLS 1903 and various other datums Goal: IGLD 2020 released to the public in 2025

  11. IGLD… How are IGLD heights made available? Dynamic heights are published by NGS on all bench mark datasheets IGLD 1985 heights are not displayed on NGS’ datasheets Hydraulic correctors are determined by CO-OPS NOS provided software can be used to convert NAVD88 heights to IGLD 1985 heights. This software applies a hydraulic corrector when appropriate. IGLD 1985 software http://www.ngs.noaa.gov/TOOLS/IGLD85/IGLD85.shtml VDatum software http://vdatum.noaa.gov/welcome.html Note: Vdatum’sIGLD 1985 function currently has a bug, with a fix in the works IGLD water levels are found on the CO-OPS water level web page at http://www.tidesandcurrents.noaa.gov

  12. The lower portion of this page is the output from the IGLD 1985 datum transformation software

  13. IGLD 1985 heights… important details Hydraulic correctors are applied to dynamic heights at locations on or very near the lake, which is assumed to be a flat surface Hydraulic correctors are not applied on sloping surfaces of rivers and connecting channels On sloping water surfaces the IGLD 1985 height and NAVD 88 dynamic height are one and the same

  14. IGLD 2020 planning IGLD 2020 will be done after adoption of a new geoid-based US vertical datum in 2022 Intent is to co-define IGLD 2020 with the new datum Vertical velocity model will be partly based on IGLD GNSS campaign surveys … 1997, 2005, 2010, 2015 and 2020. Planning for a 2015 GNSS campaign has begun.

  15. Further Information • NOAA, NOS, National Geodetic Survey www.ngs.noaa.gov • NOAA, NOS, Center for Operational Oceanographic Products and Services http://www.co-ops.nos.noaa.gov/ Data requests including IGLD 1955 and USLS 1935 contact: User Services: (301) 713-2815

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