The LSU Center for GeoInformatics (C4G) was founded in 2001 by Dr. Roy K. Dokka. Dokka was a well-respected geologist, expert in faulting, who aimed to study the tectonic activity of the Mississippi River delta area, i.e., Louisiana and the Gulf Coast.
The usual tool for such studies would be precise geodetic leveling, [link] a tedious process heavily dependent on accurate benchmarks on which to base observations using accurate orthometric corrections. Recognizing the dynamic nature of our area with post-glacial subsidence and sedimentary compaction that rendered the traditional benchmarks unreliable, he devised a scheme to use precise Global Positioning System (GPS antennae mounted on geologically stable buildings as references for his geological studies.
The National Geodetic Survey (NGS) warmed to the idea of GPS reference stations (CORS) across Louisiana and supported his efforts through a seed grant that provided equipment for a few stations. Additionally, the Louisiana Spatial Reference Center (LSRC) was created at the C4G to make the archive data available to the public. This network was named GULFnet. [link]
The local surveying community recognized the potential of such a network, and they encouraged Dokka and C4G to make the GPS data available in real-time over radio or cell phone to enhance their performance and accuracy in the field as they worked. The Real-Time-Surveying (RTS) network (RTN) was born in 2007 and would become C4Gnet. [http://c4gnet.xyz/] Today, most who know of the LSU C4G, associate it with the C4Gnet, but there is so much more going on behind the scenes. The muscle behind the C4Gnet is a world-class, robust and redundant system of servers, communication, and backups managed by the administrator, Randy Osborne, and Vasiliy Dubinin with field maintenance by Larry Dunaway.
While the loss of Dr. Dokka in 2011 meant a reduction in the geologic emphasis, the geodetic functions of the LSRC continues. Dr. Ahmed Abdalla has been added to the line-up and brings his strong background into play. The dynamic geology of the Mississippi Delta (read: Louisiana) the accuracy of the geodetic data has always deteriorated quickly following surveys by NGS, C&GS, the Army Corps of Engineers, or others. The advent of using satellites for positioning opened the possibility of improved accuracy by which the CORS became the reference benchmarks for the traditional benchmarks. As the CORS antennae moved, their locations would be tracked and known immediately, and the traditional benchmarks could be referenced to them.
Having such fiducial references meant great strides might be made in observations of other forms of geodetic data.
Ellipsoid heights of nearby benchmarks could be obtained from GPS observations.
Application of good models of the Geoid could be applied to the ellipsoid values to calculate orthometric heights (elevations).
Accurate positions and ellipsoid heights could be married with precise absolute gravity observations to develop more precise, accurate geoid models. (Defining the relationship between geometric and physical geodetic datums.
Accurate positions and heights could be married with Absolute Gravity and Deflection of the Vertical (DoV) observations to enhance modeling of the geoid.
Locating CORS close to a NOAA tide gauge enhances building the relationships between geodetic and tidal datums.
Techniques used include Satellite positioning & timing, Trigonometric tacheometry, spirit leveling, absolute and relative gravimetric observations, and astro-geodetic deflection of the vertical observations.
In each case, the CORS serve as a nexus through which all the relationships are tied.
An attempt to show schematically how it works in practice is illustrated below.
ARP -The GNSS antenna is the hub (ties are made to its reference point, the ARP)
The CORS is usually accompanied by 3 or so reference marks (RMs) and absolute gravity marks (AAs) that are tied to the CORS and each other by tacheometry, plus an RM for DoV observation.
RM1 - is set directly below the antenna, as near as practical.
AA - is set indoors (climate controlled) as near as practical, beneath the antenna.
RM# - The RM for DoV is frequently a little removed from the CORS to eliminate light pollution and on a soil surface rather than concrete to avoid high frequency noise. It is usually monumented with a magnetic monument set just below ground level. It is positioned with C4Gnet.
RM2 & RM3 are positioned using the C4Gnet to enable orientation and redundant positions for RM1 and AA marks.
The LSRC participates in many of the efforts by NGS preparatory to the publication of the 2022 datums. An important one for Louisiana is the GPSonBM project. Many of the traditional benchmarks across the state were observed redundantly for use by NGS to develop the 2022 translation and adjustment. One potential project the LSRC is considering involves making gravity observations at the GPSonBM benchmarks to develop a slope-validation-network. This will be a labor-intensive effort, but we are optimistic. The geodetic field work is performed by Fernández PE, and Jon Cliburn and managed by J. Anthony Cavell.
For more information about how LSRC practice fits in with NGS’ recommendations follow this [link] (coming soon).
The Louisiana Spatial Reference Center was founded in 2002 as a partnership between NOAA’s National Geodetic Survey and the LSU Center for GeoInformatics to create state-of-the-art positional infrastructure for the state of Louisiana and to provide technical leadership, training and access to positional data. It operates GULFnet, a network of high precision Global Navigation Satellite System receivers used as reference stations throughout Louisiana.
J. Anthony Cavell PLS, CFedS is the resident surveyor for the LSRC/C4G and serves as the State Geodetic Coordinator.
Members of the Louisiana Spatial Reference Center ensure that their gravity meter is level after moving it to their second gravity comparison spot.
NOAA's Table Mountain Gravity Observatory near Boulder, Colorado, is hosting the International Comparison of Absolute Gravimeters (ICAG) in August and September of 2023. These comparisons, which take place every four years, are certified by the International Bureau of Weights and Measures in Sevres, France. Previous ICAGs took place in Beijing, Luxembourg, and Paris.
Gravity meters measure the acceleration of a falling object near the Earth's surface and read in units known as gals or "g". The nominal value of a g is 9.8 meters per second squared, but these instruments are sensitive to an astonishing few parts per billion. The gravity at Table Mountain is about 9.79622742 meters per second squared. However, there is no place on Earth where the value of gravity is known exactly, and because there is no single, perfect instrument against which one can compare, scientists must periodically get together and compare their instruments directly.
Over 50 participants from 23 countries will meet in Boulder this summer. They will operate 38 instruments over six weeks to verify the consistency of the measurements.
This is the first international comparison to be held in North America, and will be co-organized with researchers from the National Institute of Standards and Technology. In addition to identifying and correcting any tiny offsets in the output of these instruments, activities will also include informal meetings and discussions between the visiting scientists and NOAA staff.
These gravity meters will then return to their home institutes where they are used to improve mapping, predict water flow, redefine the kilogram, study hydrology, and more.
Why C4G Has Taken On The Study of Gravity In Southern Louisiana
In March 2013, NGS made a presentation on its 2010 GNSS Height Modernization project in Southern Louisiana where they pointed out that GEOID12a produces 95% confidence at ± 4 to 8 cm in Louisiana. This is a problem since the goal of the NGS GRAV-D project is to establish a 2 cm GEOID for much of the country. The NGS conclusion states that the problem in Louisiana is too large for NGS to handle alone and that we all need to work together to get better height results. They also recommend partnering with locals (like the C4G LSRC) to leverage existing resources and that a plan needed to be created to move forward if we expect to improve heights in the 2022 vertical datum which will be based on a gravimetric geoid.
Big picture ideas NGS presented to consider regarding the GEOID problem in Southern Louisiana
Short term (through ~2015)
Extend 2009 MS leveling into and across LA
Establish GNSS infrastructure to monitor subsidence
New ~2015 GNSS Height Mod survey (gives 10-year delta time)
Medium term (~2016-2022)
Terrestrial gravity surveys
Incorporate GRAV-D aerial gravity into geoid model for region
Long term (~2022)
New vertical datum based on gravimetric geoid
Because C4G already had the GNSS infrastructure in place and in its role as the Louisiana Spatial Reference Center (LSRC), C4G was already an active Height Mod partner, in 2013, the LSU Center for GeoInformatics started actively pursuing the funding necessary to do the terrestrial gravity surveys and control work needed to create better GEOID models in Louisiana. Only by feeding well-distributed vertical control data into future GEOID models will we be able to improve the accuracy of future GEOID models. And that is perhaps our only hope of ever creating a ±2cm GEOID in the state of Louisiana.
Through funding from Height Modernization and Board of Regent grants, we acquired two relative gravity meters. C4G then self-funded an absolute gravity meter with theintention of capturing the data needed to feed future GEOID models and help NGS reach their 2 cm GRAV-D goals in Louisiana.
The Gravity of our Positions!
Physical Geodesy is the science of the variations of the Earth's gravity field. The Geodesy of Subsidence has been an active topic of research in the LSU System since the middle 1980s. The intensity of the Earth's gravity at any spot on the surface is a function of the density of the Earth's crust at that spot and the distance to the center of mass. In a homogeneous sedimentary basin (Lower Mississippi Valley and the Delta), the density is practically constant except for occasional salt domes; therefore any variation in the gravity field may be attributed directly to changes in elevation, which usually relates to subsidence in Louisiana. Some "noise" can result from significant changes in groundwater.
Relative gravity surveys have determined the magnitudes of change from one elevation benchmark to another in the Gulf Coast Region, including Louisiana but the initial starting point has necessarily had to be assumed until the advent of Absolute Gravity observations made in the early 1990s. Re-observation of Absolute Gravity in New Orleans has been performed six times since then, and each new observation has shown a constant subsidence rate of 9.1 millimeters per year (3.5 inches per decade).
In the early 2000s, the LSU Center for Geolnformatics began installing GPS receivers at public buildings throughout the State of Louisiana and has continuously recorded the heights of the receivers as they have changed through the years. Most of these sites have shown varying rates of subsidence from place to place, based solely on GPS observations. A series of Absolute Gravity observation campaigns commenced in 2002 at some of the C4G GPS CORS sites by the National Geodetic Survey, and in 2006 was observed by the National Geospatial-Intelligence Agency.
No further observations of Absolute Gravity were performed in the State of Louisiana until 2018 when the National Geospatial-lntelligence Agency returned through the official requests of C4G and the Commander, New Orleans District Corps of Engineers. NGA agreed to visit some of the C4G CORS sites based on personnel availability and scheduling, but their generosity cannot be extended to over 100 of our CORS sites! Our own FG5-X Absolute Gravity meter is now a necessity to support our two CG-5 Relative Gravity meters in our continuing campaign to observe, record, and map the ever-changing gravity field of the State of Louisiana.
The significance of this research is that traditional surveying methods used to determine elevations of benchmarks have become inordinately expensive in the 21st century, and GPS is the only technology available currently to provide observations for that purpose. The issue, however, is that GPS does NOT provide "elevations" related to the concept of "mean sea level." GPS only provides a geometric "height" with respect to the center of mass of the Earth about which the satellites orbit. A mathematical model of the Earth's gravity field is necessary to translate from "height" to "elevation," and that is called the "geoid model." Where does the geoid come from? It comes from knowledge of the Earth's gravity field.
The more exquisite the knowledge we have about the gravity field, the more accurate we then can model the geoid, providing more reliable elevations for flood insurance, flood control, planning for evacuation route changes based on continuing subsidence, and variations in subsidence rates throughout the State of Louisiana. The LSU GPS Continuously Operating Reference System (CORS) network is a public utility offered by C4G, and that network is dependent on maintaining and improving the knowledge of the geoid for elevation control in support of Louisiana Revised Statute 50:173.1 which names C4G as the State Reference Standard for elevations.
C4G Acquires Geodetic Instruments to Better Understand Subsidence Rates in Louisiana
The Center for GeoInformatics (C4G) in the Department of Civil and Environmental Engineering (CEE) recently received new geodetic instruments to model the Earth’s gravity field. A Scintrex CG-5 Relative Gravity Meter, Leica T60 Total Station, and Trimble R10 GPS Rover Kit were acquired as part of an enhancement grant sponsored by the Louisiana Board of Regents. Drs. George Voyiadjis (PI) and Joshua Kent (Co-PI) led the one-year project, which ended in June, 2017. The instruments are acquired to address the needs of three objectives: First, to develop a novel, high-resolution gravity model of sea level (i.e., geoid); second, to augment knowledge of existing subsidence rates and the driving mechanisms; and finally, promote advanced geodetic research at the University.
Here, as in many river deltas around the world, land surfaces are sinking due to subsidence. On average, southern Louisiana experiences ~10 millimeters per year of subsidence. Understanding the mechanisms that drive subsidence is essential for mitigating risk and promoting sustainability. The CG-5 relative gravity meter supports these goals by measuring the relative differences in the Earth’s gravity across southern Louisiana. Surveys using the total station and R10 rover kit are currently underway to geodetically correlate the CG-5 data with absolute gravity readings collected in the early 2000s by the National Geospatial-Intelligence Agency and the National Geodetic Survey. The updated gravimetric surveys conducted by C4G researchers and staff will deliver much needed insight into the variety of geophysical processes driving the spatially and temporally heterogeneous rates of subsidence measured across the state.
In addition to the subsidence research, this enhancement grant will directly and indirectly benefit Louisiana’s geodetic stakeholder and consumer communities. For nearly a decade, the C4G has provided tools, services, and other geodetic resources dedicated to precise positioning throughout the state and across the region. Central to these resources is the C4GNet real-time reference network. The network includes more than 50 continuously operating GPS reference stations (CORS) installed across Louisiana. Over the next five years, the C4G plans to geodetically correlate the gravity measurements with antenna heights at each station. Extended surveys will include CORS in neighboring states. When completed, the data will contribute to the creation of a novel, high-resolution geoid model that will allow the geodetic community to accurately and precisely measure elevations above sea level.
Geodetic Research
The instruments acquired by this grant represent an investment into the geodetic research capacity at the C4G and CEE. In addition to the above goals and objectives, these resources have already been selected for use by investigators in two external funding proposals, both of which will rely on the precision of these instruments to deliver meaningful geodetic solutions. These instruments not only promote research activities, they have galvanized national and international collaborations with partners across the US Gulf Coast and western Europe.
First Louisiana Gravity Campaign of 2018 Report Completed
The United States National Geospatial-Intelligence Agency (NGA) has delivered its final report of their first Absolute and Relative Gravity Survey of February-March 2018. The survey has been conducted in support of requests from the New Orleans District, U.S. Army Corps of Engineers (USACE) and the Center for GeoInformatics of the Department of Civil and Environmental Engineering, Louisiana State University.
Louisiana is in a known area of geological crustal motion, and most elevation benchmarks are sinking due to a phenomenon of regional subsidence. For centuries, Engineers and Land Surveyors have relied on known reference points known as benchmarks for elevations to determine proper heights for establishing buildings and flood control structures. In Louisiana, those elevation benchmarks continue to subside and the elevations once associated with those points become stale, out-of-date or wrong! Current technology allows surveyors to employ the GPS satellites for a variety of applications, and the determination of elevations is one of the more important applications for the citizens of Louisiana. GPS gives positions that need additional information in order for Engineers and Land Surveyors to determine elevations, and that additional information is the Earth’s gravity field.
The Earth’s gravity field in Louisiana is not precisely known to the exquisite detail necessary for GPS surveyors to determine elevations to fractions of an inch. LSU is in the process of investigative research to better determine the variation of the gravity field in the State of Louisiana. Research into the study of the Earth’s gravity field with respect to subsidence was started in the LSU System in the late 1980’s. The U.S. National Geodetic Survey made the first observations of Absolute Gravity in Louisiana back in March, 1989. Subsequent re-surveys were done in September, 1991, November, 1993, and August 1994. Each time, the observations indicated continuous subsidence in metropolitan New Orleans at a constant rate of 9.1 millimeters per year or more than an inch every three years! These observations are used to understand the rates of subsidence in varying parts of Louisiana, and to monitor any variations in subsidence rates from one observation epoch to another. This is how Engineers and Planners utilize such scientific data in determining future efforts for flood control and disaster evacuation.
NGA has submitted their report on their first gravimetric campaign, and have observed at the LSU campus, the LIGO facility in Livingston Parish, Hammond, Nicholls State University, and the University of New Orleans. NGA personnel will return to Louisiana in the fall for their second gravimetric campaign of 2018. This work represents the second generous donation of time (first time in 2002) and services to the citizens of Louisiana by the United States Department of Defense NGA for the support of flood protection facilities maintained by the New Orleans District, Corps of Engineers.
The LSU Center for GeoInformatics (C4G) has purchased and received the first university-owned Absolute Gravity Meter in the Southeastern United States. The importance of this acquisition is that all elevation reference data in Louisiana is subject to subsidence. The federally published values of elevation benchmarks only last 3-5 years in all of South Louisiana, somewhat longer as one goes north. The nation’s engineers and land surveyors are now dependent on GPS observations to get elevation data, but GPS does not provide elevations with respect to local mean sea level (datum); GPS only provides “geometric” heights. A precise knowledge of the Earth’s gravity field is necessary for the conversion from GPS heights into elevations. Flood insurance is dependent on the results of flood elevation surveys performed by engineers and land surveyors, as well as planning for evacuation routes in anticipation of impending hurricane flooding. The Absolute Gravity instrument now held by C4G is the basis for refining the accuracy of the Earth’s gravity field, and by being “absolute,” the instrument employs a basic fundamental reference traceable to the U.S. National Institute of Standards and Technology (NIST).
For decades, the LSU System has relied on Federal Agencies to come into Louisiana from time-to-time in order to observe the changes in the absolute gravity in the State. The U.S. National Geodetic Survey (NGS) first observed absolute gravity in New Orleans in 1989. The NGS has returned over a half-dozen times since then as well as at numerous other sites. Also, with the help of the New Orleans District, U.S. Army Corps of Engineers; the U.S. National Geospatial-Intelligence Agency (NGA) has also performed several absolute gravity campaigns in the State, the most recent one was observed in early 2018. As absolute gravity increases, the changing values indicate actual subsidence of the surface of the observation site and the distance to the center of the Earth. The instrument, an “FG5-X,” made by Micro g LaCoste in Colorado, has a precision of ± one micro-gal (± 1 µg) such that a change of 3 µg = one centimeter (1 cm) in elevation!
The LSU C4G is the legal standard (Law) in the State of Louisiana for State Government agencies to obtain elevation references per LA R.S. 50:173.1. The C4G has purchased the FG5-X Absolute Gravity meter ($400,000) with C4G self-generated funds – no use of tax dollars contributed to the purchase. The C4G has installed GPS Continuously Operating Reference Stations (CORS) throughout the State as well as at Tide Gauges throughout the Northern rim of the Gulf of Mexico from Corpus Christi, Texas to Jacksonville, Florida. The FG5-X Absolute Gravity meter will be employed to observe at all LSU CORS sites in the future on a continually-revolving basis in order to track the crustal movement of subsidence, its changing values, and the changes in the rates of subsidence. Intermediate points of elevation, the passive benchmarks monumented throughout the Gulf South, will be observed and re-observed by Relative Gravity meters owned by C4G along with the Absolute sites being used as reference standards.
All of these gravity observations, both Absolute as well as Relative will be the basis for the precise mathematical model of the Earth’s gravity field called the “geoid.” The geoid model is the mathematical model of the gravity field that engineers and land surveyors use to convert precise GPS heights into elevations. As subsidence continues to occur in Louisiana and surrounding regions, the actual geoid will change also. This necessitates the continuing observation of the absolute and relative values of gravity in the continual modeling and re-modeling of the geoid. The frequency of repeat gravity campaigns will be determined by experience gained through the monitoring of the gravity observations and the rates of change.
The Center for GeoInformatics (C4G) in the Department of Civil and Environmental Engineering (CEE) recently received new geodetic instruments to model the Earth’s gravity field. A Scintrex CG-5 Relative Gravity Meter, Leica T60 Total Station, and Trimble R10 GPS Rover Kit were acquired as part of an enhancement grant sponsored by the Louisiana Board of Regents. Drs. George Voyiadjis (PI) and Joshua Kent (Co-PI) led the one-year project, which ended in June, 2017. The instruments are acquired to address the needs of three objectives: First, to develop a novel, high-resolution gravity model of sea level (i.e., geoid); second, to augment knowledge of existing subsidence rates and the driving mechanisms; and finally, promote advanced geodetic research at the University.
Here, as in many river deltas around the world, land surfaces are sinking due to subsidence. On average, southern Louisiana experiences ~10 millimeters per year of subsidence. Understanding the mechanisms that drive subsidence is essential for mitigating risk and promoting sustainability. The CG-5 relative gravity meter supports these goals by measuring the relative differences in the Earth’s gravity across southern Louisiana. Surveys using the total station and R10 rover kit are currently underway to geodetically correlate the CG-5 data with absolute gravity readings collected in the early 2000s by the National Geospatial-Intelligence Agency and the National Geodetic Survey. The updated gravimetric surveys conducted by C4G researchers and staff will deliver much needed insight into the variety of geophysical processes driving the spatially and temporally heterogeneous rates of subsidence measured across the state.
In addition to the subsidence research, this enhancement grant will directly and indirectly benefit Louisiana’s geodetic stakeholder and consumer communities. For nearly a decade, the C4G has provided tools, services, and other geodetic resources dedicated to precise positioning throughout the state and across the region. Central to these resources is the C4GNet real-time reference network. The network includes more than 50 continuously operating GPS reference stations (CORS) installed across Louisiana. Over the next five years, the C4G plans to geodetically correlate the gravity measurements with antenna heights at each station. Extended surveys will include CORS in neighboring states. When completed, the data will contribute to the creation of a novel, high-resolution geoid model that will allow the geodetic community to accurately and precisely measure elevations above sea level.
The instruments acquired by this grant represent an investment into the geodetic research capacity at the C4G and CEE. In addition to the above goals and objectives, these resources have already been selected for use by investigators in two external funding proposals, both of which will rely on the precision of these instruments to deliver meaningful geodetic solutions. These instruments not only promote research activities, they have galvanized national and international collaborations with partners across the US Gulf Coast and western Europe. More information about these instruments and geodetic models is available at the C4G website www.c4g.lsu.edu or gravity.c4g.lsu.edu.
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.”
Big picture ideas NGS presented to consider regarding the GEOID problem in Southern Louisiana
The significance of this research is that traditional surveying methods used to determine elevations of benchmarks have become inordinately expensive in the 21st century, and GPS is the only technology available currently to provide observations for that purpose. The issue, however, is that GPS does NOT provide "elevations" related to the concept of "mean sea level." GPS only provides a geometric "height" with respect to the center of mass of the Earth about which the satellites orbit. A mathematical model of the Earth's gravity field is necessary to translate from "height" to "elevation," and that is called the "geoid model." Where does the geoid come from? It comes from knowledge of the Earth's gravity field.
The Center for GeoInformatics (C4G) in the Department of Civil and Environmental Engineering (CEE) recently received new geodetic instruments to model the Earth’s gravity field. A Scintrex CG-5 Relative Gravity Meter, Leica T60 Total Station, and Trimble R10 GPS Rover Kit were acquired as part of an enhancement grant sponsored by the Louisiana Board of Regents. Drs. George Voyiadjis (PI) and Joshua Kent (Co-PI) led the one-year project, which ended in June, 2017. The instruments are acquired to address the needs of three objectives: First, to develop a novel, high-resolution gravity model of sea level (i.e., geoid); second, to augment knowledge of existing subsidence rates and the driving mechanisms; and finally, promote advanced geodetic research at the University.
ded surveys will include CORS in neighboring states. When completed, the data will contribute to the creation of a novel, high-resolution geoid model that will allow the geodetic community to accurately and precisely measure elevations above sea level.
