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November 26, 2018
BATON ROUGE, LA – Throughout the month of October, 10 members of the National Geospatial-Intelligence Agency visited LSU’s campus and other statewide GPS sites to take gravity measurements for a research project spearheaded by LSU Center for Geoinformatics (C4G) Chief of Geodesy Cliff Mugnier.
Every five to 10 years, the NGA takes measurements of the earth’s gravity field to check for subsidence, a project Mugnier has been working on for nearly 30 years.
“LSU has the largest university-owned network of permanent GPS stations in the world, which reach from Louisiana throughout the Gulf Coast,” Mugnier said. “Over the years, I have asked the military to come in to take measurements at these stations. I first go to the New Orleans Corps of Engineers, whose colonel then writes a letter to the Pentagon asking if they can come to Louisiana and observe different places where we have our GPS antennas for our research on subsidence. The idea is if you come back to the same spot over a period of years and see an increase in the strength of the earth’s gravity, that means you’re getting closer to the center of the earth, which equates to subsiding.”
The NGA kicked off its recent Louisiana trip at LSU’s Absolute Gravity Station using instrumentation similar to the FG5-X Absolute Gravity meter that C4G purchased this year. C4G also houses two CG5 Relative Gravity meters. From LSU, the NGA team—consisting of two groups of five trainees from New Mexico, Whiteman Air Force Base in Missouri, and both the East and West Coasts—moved on to other GPS core sites across south Louisiana that included Oakdale, Alexandria, New Orleans, Slidell, Boothville, Lafayette, Lake Charles, Cocodrie, and Grand Isle. The NGA will take measurements in north Louisiana this winter to conclude their 2018 Louisiana campaign.
“The reason for these gravity measurements is to have a completely independent physical measurement of vertical movement as a function of gravity, rather than readings from the GPS satellites,” Mugnier said. “It all fits together for the subsidence research, but another reason is when people mortgage their homes, the banks require them to have flood insurance, which is based on elevation. The Corps [of Engineers] is also interested in subsidence because they have the responsibility of levees and flood control.”
The NGA hasn’t visited Louisiana since 2003, shortly after Mugnier arrived at LSU. Though subsidence is of vast importance to Louisianans, the NGA does not take measurements every year because subsidence is a slow process.
“If you do it too frequently, the observations get lost in what is called white noise,” Mugnier said. “Even though the instruments are super precise, you still have to have the time for the sinking to be enough for the instruments to detect.”
Mugnier’s research on Louisiana subsidence began when he taught at the University of New Orleans, where the first NGA measurements were taken in 1989. Since then, research has shown that UNO’s campus is sinking at a rate of 9.1 mm/year, which Mugnier said is significant when you consider that equates to 3 feet in 100 years.
“Three feet is a whole lot when you also consider sea level is rising about 2 mm each year,” he said.
Since the first reading taken at LSU around 2003 by the National Geodetic Survey, it has been discovered that LSU’s campus is subsiding around 5 mm/year near the fault line on Nicholson Drive. The campus is on the downside of the fault.
Since subsidence is an unstoppable force, Mugnier has made sure that C4G will continue his research when he is no longer at LSU. The man who started C4G, LSU Professor Roy K. Dokka, established the organization whose mission is in keeping with state law that says C4G is the source to keep track of elevations for the state of Louisiana.
“So, we have an organization that’s going to be here long after I’m gone,” Mugnier said. “And we have the perfect research project that will go on forever.”
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Louisiana State University’s Center for GeoInformatics (C4G) in its role as the Louisiana Spatial Reference Center (LSRC) has been awarded a grant for $3.1 million over the next five years (2018-2023) from the National Oceanic and Atmospheric Administration (NOAA) for their support in the Regional Geospatial Modeling. The Principal Investigator and Project Director is Boyd Professor George Z. Voyiadjis, Director of the C4G with Co-Investigators Randy L. Osborne, Clifford J. Mugnier and J. Anthony Cavell. Larry Dunaway and Jon Cliburn round out the investigating team.
The LSRC’s grant awarded in collaboration with a continuing 5-year Gulf Coast-wide partnership among Mississippi, Texas, Louisiana, Florida and Alabama; is to support the improvement and modernization of NOAA’s National Spatial Reference System (NSRS). Key to these efforts will be the collection of accurate, precise, and consistent geospatial data to improve regional geospatial models and to coordinate the use of this geospatial data by users to improve the NSRS for the states bordering the northern Gulf of Mexico. Partnership outreach efforts will bring awareness, access, and education to users of the NSRS. The geospatial data resources produced through the partnerships will improve NSRS Height Modernization efforts across the entire northern Gulf of Mexico coast.
The LSRC at Louisiana State University proposed a unified, regional partnership that will focus on the following objectives as the Louisiana portion of the broader proposal package submitted by the University of Southern Mississippi.
LSRC will work to enhance the infrastructure of geodetic control, coastal remote sensing data, terrestrial gravity measurements and other physical datasets. Various means will be used which include deploying two Scintrex CG-5 Relative Gravity Meters that were purchased at a cost of $100K each under prior grants, one from a NOAA/NGS height modernization grant and another from an LSU Board of Regents grant. C4G’s new self-funded $400K Micro-g LaCoste FG5-X Absolute Gravity Meter will be deployed to collect terrestrial gravity measurements at the C4G’s Continuously Operating Reference Stations (CORS), NSRS benchmarks, and LSRC eccentric benchmarks, which will allow LSRC to improve the geodetic modeling for future datums and NSRS modernization.
Several newly acquired pieces of equipment will be used for these observations. The Scintrex Trident Tripod, which in conjunction with C4G’s CG-5 Relative Gravity Meters will be used to observe the Gravity Gradient by accurately positioning the gravity meter at three predetermined levels for quick and precise measurements. The LSRC will acquire through the NOAA grant a $100K Digital Zenith camera in the first year of this grant from the Institute of Geodesy and Geoinformatics located at the University of Latvia and use this new instrument to measure the vertical deflection at CORS sites. The deflection of the vertical is a measure of how far the gravity direction has shifted, caused by local anomalies, which helps increase the accuracy of local surveys of the Earth’s gravity field.
LSRC will also collaborate with NASA’s Jet Propulsion Lab (JPL) in order to investigate targeting methods using InSAR to track regional subsidence to help develop guidelines and tools to access geodetic control and to manipulate and analyze geodetic data.
LSRC continues to maintain its existing geospatial data clearinghouse it established to provide free access to information that includes CORS raw data, flood maps, satellite, and aerial photography, digital elevation models (e.g., LiDAR, RADAR, and InSAR), and other relevant assets necessary for regional geospatial modeling.
The national goal is to develop models with accuracies better than 2 cm (3/4 in.). The dynamic nature of Louisiana’s geology makes it an outlier when continental geodetic models are developed, with many negative results for Louisiana. The LSU C4G has demonstrated the ability to observe precise terrestrial gravity, elevations and geometric relationships to the degree necessary for improving the geodetic models. Observing and possibly predicting subsidence in south Louisiana and along the Gulf Coast has been an acute challenge recognized since the 1950s, and becomes more acute with time. The NOAA grant seeks to build on the work of the LSU C4G that shows promise of bringing Louisiana, and the Gulf Coast into the norm, permitting accurate geoid models, flood mapping, coastal studies, levee construction and public safety in general.
The Center for GeoInformatics was created in 2001 to build new research and services in Geodesy and Geoinformatics for the geodetic and geophysical communities. The C4G, in cooperation with NOAA’s National Geodetic Survey (NGS), founded the Louisiana Spatial Reference Center in 2002 as a partnership focused on a state-of-the-art positional infrastructure for the state of Louisiana and to provide technical leadership, training and access to positional data. LSRC is responsible for the network of GNSS control stations; a reliable spatial reference system in Louisiana (GULFnet). The C4G maintains the GNSS Real Time Network (C4Gnet), established in 2007 to serve surveying, mapping, utilities, emergency response, agriculture, forestry, public safety, transportation, machine control for construction, environmental, and scientific research. – Positioning Louisiana for the Future.