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Procedures for connecting SET bench marks to the NSRS : establishing GNSS-derived ellipsoid/orthometric heights on surface elevation table bench marks
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Procedures for connecting SET bench marks to the NSRS : establishing GNSS-derived ellipsoid/orthometric heights on surface elevation table bench marks
  • Alternative Title:
    Establishing GNSS-derived ellipsoid/orthometric heights on surface elevation table bench marks
  • Description:
    "These guidelines were developed in response to a growing interest in accurately measuring local sea level rise in relation to coastal land elevation. Central to this task is obtaining accurate and precise connections between wetland surface elevation and local water levels. For over a decade, Surface Elevation Tables (SETs) have been used to measure and monitor coastal wetland surface elevation with respect to an in situ vertical bench mark. However, these bench marks, often located in remote coastal settings, have traditionally been isolated from consistent spatial reference. These guidelines were developed to provide the necessary information to bring ellipsoidal heights to SET bench marks via Global Navigation Satellite System (GNSS) technology. Once vertical control has been established in a coastal wetland setting, other coastal observing systems can likewise be connected, such as local water level recorders, permanent vegetation monitoring plots, etc. Furthermore, by connecting SET bench marks to a consistent vertical framework, the vertical velocity of the bench mark can be measured over time, providing information on local rates of deep subsidence. Bringing accurate and precise elevations to remote coastal wetland settings is fraught with difficulties and logistical constraints. Surveying has traditionally avoided the typically unstable, unconsolidated, and very dynamic wetland soils. Survey methods have to be adapted to this environment, also taking into consideration minimizing impacts to the sediment surface which is being measured. This document draws on extensive field trials conducted at SET sites distributed across southeastern Louisiana, in collaboration with the University of New Orleans, the US Geological Survey, and the Louisiana Department of Natural Resources. The main body of this manual provides the user with basic information on how to conduct a GNSS campaign in coastal wetland settings. The document is designed to help the user decide where and when to use static GNSS observations on SET foundations, and when to use Real-Time Kinematic GNSS (RTK) techniques. Guidelines are given for conducting both types ofcampaigns. The guidelines cover procedures from designing to the execution of a GNSS campaign, and the subsequent data processing and submission. A detailed glossary is given, including the acronyms used throughout the text. The main body of the guidelines concludes with a list of references. In one of several attachments, the guidelines provide several examples of static and RTK campaigns that were conducted in southeast Louisiana. Another attachment provides detailed information on how to establish a vertical point of reference on a SET bench mark. The third and fourth attachments describe the use of two different custom-made GNSS antenna adapters for SET foundations. Finally, the fifth attachment provides guidelines on how to transfer the elevation of a SET foundation to the height of the SET measuring instrument when it is deployed on the foundation. This allows individual observations of wetland surface elevation to be expressed in relation to a vertical geodetic datum"--Purpose and scope of document.
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