Updated Elevations for Coastal Louisiana - 2004
NOTICE: Updated elevation information is now available for coastal Louisiana south of Interstate 10. The GEOID03 model for this area has also been updated. This information should be incorporated into all recent, current, or planned surveying efforts in this region which are elevation sensitive. Click on the map for updated survey information for coastal Louisiana or download a table of updated stations. |
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Contact NGS or the Louisiana Spatial Reference Center for updated or additional information on bench mark elevations and additional GPS sites in coastal Louisiana for the area south of Interstate 10.
Background
Subsidence affects the elevation of the land. In areas where survey marks cannot be “anchored” to an immovable mass movement occurs, and as a result, elevations change over time.
The National Geodetic Survey (NGS) and the Louisiana Spatial Reference Center (LSRC) at Louisiana State University have provided an analysis of the historic vertical control (leveling) network. NGS has validated the heights of 85 existing bench marks using GPS, subsidence rates, and an improved geoid model. The data sheets for these Vertical Time-dependent Positioning (VTDP) stations have been updated. Furthermore, these stations will be included in the Re-adjustment of the National Spatial Reference System to be released in February 2007.
Now we need your help.
The updated VTDP bench marks MUST be used to determine VALID orthometric heights referenced to NAVD 88 for all applications of elevation information in coastal Louisiana. Failure to use this set of VTDP bench marks with their updated elevations will result in elevations that are not consistent with the new network.
For surveys already completed --
If you have recent survey data that does not use any of these stations for control purposes, additional observations between your vertical control stations and 3 (at a minimum) bench marks will allow for the transfer of the recent improved NAVD 88 heights. The more marks you use, the more confidence you build into your projects and into the network.
New projects
Design new projects to include as many VTDP bench marks as possible, and no less than 3, in your project area. The larger the project area, the more stations you need to include. Contact NGS or LSRC for guidance.
Use National CORS data in your project as well as any other local GULFNET or temporary TIGER station in the area. This will provide a horizontal and ellipsoid height control to the project.