Center for GeoInformatics / Louisiana Spatial Reference Center

Subsidence is the underlying culprit behind Louisiana's greatest environmental problem, the continuing loss of our coast. In addition to being a world-class scientific topic, coastal land loss robs the State of 25-35 square miles per year due to both natural and man-made causes. Subsidence has also had the serious effect of disturbing the system of reference markers we use for surveying the elevations of levees, evacuation routes, coastal restoration efforts, etc. To address these problems, the Center for GeoInformatics at Louisiana State University, in cooperation with the National Geodetic Survey (NGS), founded the Louisiana Spatial Reference Center (LSRC) in 2002. Through a grant from National Oceanic and Atmospheric Administration (NOAA), LSRC installed a network of high precision Global Positioning System (GPS) receivers used as reference stations throughout Louisiana, by 2005 the network had grown to 40 stations state-wide.  

Once in place, this network of GPS continuous operation reference stations (CORS) was used to re-establish the official federal reference system within the state. Louisiana State Legislator made LSRC’s CORS network the vertical control standard for Louisiana in 2006 with Act 194, Section 1.R.S. 50:173.1.  C4G uses this system to focus research on pinpointing the location of subsidence and measuring exactly how fast the coast is sinking. Subsidence in Louisiana makes the roads more likely to flood. LSRC's efforts in Height Modernization help to predict how much certain areas will flood before a storm begins. Accurate heights alert safety planners to storm evacuation routes that are slowly sinking and susceptible to storm surges.

Committed to making transportation and navigation safer, LSRC assists NGS in conducting aerial photography surveys and elevation surveys of Hurricane Evacuation routes. LSRC also assists NGS in mapping the coastal regions of Louisiana and provides data for navigational charts. Accurate heights also provide ships with safe under-keel and overhead clearance to avoid dangerous collisions. Data from this infrastructure also provides the needed information to support future coastal restoration efforts.

In 2007 C4G launched a Real-Time Network utilizing LSRC’s state-wide GPS CORS infrastructure and termed the RTN GULFNet. A second RTN termed C4Gnet was introduced in 2012, running on the next generation of infrastructure software. Both RTN’s are online currently and have over 66 CORS stations, 27 of which are National CORS that the NGS coordinates and monitors to form Louisiana’s part of the National Spatial Reference System (NSRS).

LSRC’s state-wide infrastructure currently provides the backbone for all surveying in Louisiana as well as provides the foundation for transportation and communication; GIS development; detailed topographic mapping and charting; precision farming; navigation and a multitude of scientific and engineering applications in Louisiana.

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    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. Read more...
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Tectonic subsidence
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Description
Tectonic subsidence is the sinking of the Earth's crust on a large scale, relative to crustal-scale features or the geoid. The movement of crustal plates and accommodation spaces created by faulting create subsidence on a large scale in a variety of environments, including passive margins, aulacogens, fore-arc basins, foreland basins, intercontinental basins and pull apart basins. Three mechanisms are common in the tectonic environments in which subsidence occurs: extension, cooling and loading. Mechanisms Extension Where the lithosphere undergoes horizontal extension at a normal fault or rifting center, the crust will stretch until faulting occurs, either by a system of normal faults (which creates horsts and grabens) or by a system of listric faults. These fault systems allow the region to stretch, while also decreasing its thickness. A thinner crust subsides relative to thicker, undeformed crust. Cooling In areas of crustal thinning, the mantle may melt due to decompression, causing the asthenosphere to rise to the surface, heating the overlying plates. Heating of the lithosphere decreases its density and uplifts the crust due to its positive buoyancy compared to the undeformed cooler crust. Once the heating ceases, the thinner crust slowly cools and becomes heavier (post-rift subsidence). Read more...

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Center for GeoInformatics
101 LSU Student Union Building
LSU Box #25413
Baton Rouge, LA 70803

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Louisiana State University
Eng. Research & Development Bldg.
Room 200, 2nd Floor
South Stadium Drive

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Cliff 225.578.4578
Randy 225.578.4609
Josh 225.578.5260
Larry 225.578.8925