On June 21, 2012, the following resolution was passed in Chalmette, Louisiana:
RESOLUTION NO. 06-21-12-10 – NATIONAL SPATIAL REFERENCE SYSTEM ELEVATIONS
WHEREAS, the Southeast Louisiana Flood Protection Authority-East needs and desires to have a consistent and reliable reference system for the determination of correct elevations; and
WHEREAS, the United States National Geodetic Survey has had the Congressional Charter to provide correct elevations for the nation since its inception in 1806; and
WHEREAS, the State of Louisiana has recognized the National Geodetic Survey (NGS) and its implementation of the program of Height Modernization for the National Spatial Reference System (NSRS) of the country; and
WHEREAS, the Louisiana State University Center for GeoInformatics has established a network of GPS Continuously Operating Reference System (CORS) sites throughout the State of Louisiana for the realization of the NGS Height Modernization program for the NSRS; and
WHEREAS, the Louisiana State Legislature has passed a law for vertical control reference within the State as LA Revised Statute 50:173.1.
BE IT HEREBY RESOLVED, that the Southeast Louisiana Flood Protection Authority-East hereby declares that the Louisiana State University Center for GeoInformatics Real Time Network of GPS Continuously Operating Reference System (CORS) is to be the sole reference system for the determination of NSRS elevations within its area of responsibility.
The standards of practice to follow for the proper utilization of Real Time Networks are:
The C4GNet (NAD83/2011) is a real-time network RTK system operated by the LSU Center for GeoInformatics. There are presently over sixty-five LSU CORS distributed throughout the state of Louisiana. A subscription to this system enables end-users with a single RTK rover to conduct surveys anywhere within the state and achieve precisions that meet or exceed that attainable through classical or standard single base-station RTK methods (Louisiana REV. STAT § 50:173.1).
To reliably achieve these precisions, all relevant National Geodetic Survey (NGS) guidelines in regard to standard RTK procedures are required for the use of C4GNet RTN (PDOP and elevation mask, fixed solution only, horizontal and vertical rms, etc.). In addition, specific calibration procedures must also be carried out in order to achieve the required accuracies. These procedures are described below.
The currently adopted geoid model (Geoid12a) shall be loaded onboard and properly utilized by the RTK rover/data collection system.
The proper antenna profile shall be utilized and the antenna make, model number, and L1/L2 phase-center offsets from the Antenna Reference Point (ARP) shall be noted in the project field book together with the correct ARP height (fixed height rods shall be utilized).
Following system initialization at the project site, but prior to the commencement of any survey data collection session, the raw C4GNet RTN derived elevation (being the average of a minimum of three minutes of one-second epoch data) of the nearest validated project or local control point of a recent NGS-published epoch shall be observed and logged, both digitally in the data collector file and in hardcopy in the project field book (with a site sketch showing sufficient descriptive detail to unambiguously identify the control station and the date and time at which it was surveyed).
The measured difference or offset between the observed and given elevation (NGS-published epoch) of the control point shall then be used to calibrate or index the output of the RTK rover/data collection system to the control point. Once the RTK rover/data collection system has been calibrated or indexed, the control point shall then be re-observed to confirm that the output elevation matches the given elevation. This re-observation shall be logged digitally and in the project field book. Once initial calibration is complete, a second validated project or local control point (of the same NGS-published epoch) shall be observed with the calibrated RTK rover/data collection system and the results logged digitally and in the project field book. If the observed elevation is within 0.15 feet of the given elevation of this second point, data collection may proceed; if not, contact SLFPAE immediately for further instruction.
In performing certain surveys (e.g., centerline profile surveys of earthen levees), motorized vehicles may be used. If a vehicular platform is used in data collection, the forward speed during collection shall at no time exceed ten miles-per hour and the data collection epoch or interval shall be two seconds or less. Additionally, the appropriate digital feature code shall be selected and used. Great care shall be taken to ensure that the vehicular antenna mount is secure, free from obstruction, and placed so that acquisition along the levee top (highest point) is assured. A detailed sketch, showing the location of the antenna on the vehicle and the offset from natural ground to ARP, shall be included in the project field book. A note describing the general levee condition, the start and stop times of the vehicular data logging session, and a diagram of the start and stop locations (showing detail of transitions to/from wall structures, for example) shall be included in the project field book.
Surveys of the top of sheet-pile walls, I-walls, or T-walls shall be conducted on foot at a data collection interval of not more than 100 feet per survey observation and at all abrupt grade changes in excess of 0.25 feet. A detailed sketch of the wall system, the height of the wall above the adjacent ground or earthen levee, the wall thickness, and the side of the wall at which the measurement was made (protected or flood side) shall be noted in the project field book.
On August 15, 2012 the first 8-hour training session was held at the Orleans Parish Levee District Offices.