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.

Bill Henning, NGSThe LSU Center for GeoInformatics hosted a training session on Best Methods to Achieve Accurate, Repeatable Orthometric Heights Using Real Time GNSS Networks. The event was held at the Orleans Parish Levee District Offices in New Orleans, Louisiana on August 15th 2012. The event was attended by over 60 individuals including surveyors, engineers, local, state and federal government officials. 

Some of the topics covered were:

  • Vertical Geodetic Control in Southern Louisiana
  • Providing the National Spatial Reference System in dynamic regions
  • Intro to GNSS
  • Guidelines for Establishing GPS-derived Ellipsoid Heights
  • Guidelines for Establishing GPS-derived
  • Orthometric Heights
  • Improvements to the Geoid Model
  • Real-time Kinematic Surveying and Best Practices
  • Introduction to Real-time Networks

The South Louisiana Flood Protection Authority District - East has made these trainings a Requirement for Professionals Working for the Levee District. Surveyors and Engineers that attended also received 8 Continuing Education Credits. The training provided professional Land Surveyors the requisite training to properly use an RTN system such as GULFNet or C4Gnet to provide current correct elevations. The main speaker was Bill Henning of NGS, one of the premier experts in the GNSS applications field. Registration, food and refreshments were handled by LSPS District 1 and plans are currently in the works to host additional events of this type in Baton Rouge and Shreveport in the near future.

If you are interested in attending one of these training events please sign up for the C4G mailing list or follow C4G in social media on Twitter, Facebook or the C4Gnet RSS feed. You can also find Podcasts, PDF's and Videos of past events on the C4G website or the C4G YouTube channel.

POSITION REPORT

GNSS Market Research and Analysis GPS/GNSS Networks and Services The Global Market for GNSS Augmentation Infrastructure and Services 2009-2013 March 2009 Abstract ©Position One Consulting Pty Ltd 2009 All rights reserved Authors Robert Lorimer & Eric Gakstatter

Global Navigation Satellite Systems (GNSS) include the United States GPS (the most commonly used today), Russia's Glonass, the EU's Galileo, China's Compass, the Indian Regional Navigation Satellite System (IRNSS) and Japan's Quasi-Zenith Satellite System (QZSS).

The signals from all these GNSS are subject to a myriad of errors and may not always tell the truth. Whereas this is not a problem for casual users or those who can tolerate such errors, there are many applications where integrity and accuracy must be improved.

C4G CORS used in C4Gnet and GULFNet Real Time Networks have been valued at over 33 Million dollars a year according to a new government report released June 15th, 2009. The report titled "Socio-Economic Benefits Study: Scoping the Value of CORS and GRAV-D" was prepared for the National Geodetic Survey by Irving Leveson. It shows billions in estimated benefits from NOAA Positioning Products and Services:

• National Spatial Reference System (NSRS): $2.4 billion per year
• CORS: $758 million per year. (C4G has 27 of the 1324 National CORS)
• C4Gnet and GULFNet have 66 CORS with a yearly valuation of $500K each.
• GRAV-D (Once completed): $4.8 billion over 15 years, including $2.2 billion in avoidance costs from improved floodplain management.

Download the entire report!

Note that the LSU Center for GeoInformatics is actively pursuing the funding necessary to do the control work needed to create better GEOID models in Louisiana. Feeding well distributed vertical control data into future GEOID models will improve the vertical accuracy of these models and is perhaps our only hope of ever creating a ±2cm GEOID in the state of Louisiana.

The NGS presentation on Friday March 15, 2013, pointed out that GEOID12a produces 95% confidence at ± 4 to 8 cm in Louisiana. The NGS conclusion states that the problem is too large for NGS to handle alone and we all need to work together to get better height results. They also recommend partnering with locals to leverage existing resources and that a plan needed to be created to move forward with improving heights.

NGS plot shows GEOID12a produces 95% confidence at ± 4 to 8 cm in Louisiana

The presentation was given by NGS geodesists / scientists, Michael Dennis and Dan Roman.

  • Michael Dennis was the recent project manager for the new adjustment to the North American Datum of 1983, NAD 83 (2011), and performed the S. LA project vertical adjustment.
  • Dan Roman is the head of research and development of geoid models at NGS.

Big picture ideas to consider from the presentation

  • Short term possibilities (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

Recently, NOAA’s National Geodetic Survey released updated orthometric heights for Southern Louisiana relative to the September 2010 GNSS Height Modernization project. These heights represent the most up to date heights available for the region. On March 15, 2013, NGS hosted a free, on-line webinar to present the results of this project.

 

Visit the NGS page for this event

To download the .mp4 file, click here.

Link to the presentation: