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Home arrow Archives   The American Surveyor     

Recent Activities at the National Geodetic Survey—Part 4 of 4 Print E-mail
Written by Dr. D. Smith, D. Graham, K. Fancher, E. Little, C. Gallagher, G. Imahori, and A. Bilich   
Sunday, 05 April 2015

A 2.853Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

Washington Monument Survey
The August 23, 2011 earthquake in Virginia shook the Washington D.C. region strongly enough to damage the Washington Monument. A repair project was initiated shortly thereafter, and to accomplish this task scaffolding was erected, encasing the monument from base to tip. And just like the last two times such scaffolding surrounded the monument (1999 and 1934), NGS sent a crew on site to survey from the peak, only this time things were a little different than before.

In 1934, the Coast and Geodetic Survey performed a triangulation survey from the peak, sighting to various visible markers around the national capital area. In 1999, the primary purpose was to demonstrate the relatively new (at the time) "Height Mod" style of performing a GPS survey. Neither of those surveys was accurate enough to serve as a baseline for "change determination" by 2014. This time around, the primary purpose was to provide a baseline for future surveys by positioning the peak within the NSRS with greater accuracy than ever before. As a side-product (geodetically speaking), but of generally greater interest to the public, the architectural height of the monument was also determined to greater accuracy than ever before.

Many of the lessons of the past, particularly from 1999, served to guide NGS in this new survey. For example, while GPS data was collected at the peak, it was expected to (and did) suffer from significant multi-path issues due to the surrounding scaffolding. As such, a terrestrial survey, including the use of reciprocal angles and distances from the peak to multiple ground stations was the primary method of positioning the peak relative to the ground points. GPS and lineof-sight measurements were used to validate the ground control horizontally. A first order, class II leveling survey validated not only the heights of geodetic control marks in the ground (including those used to measure the architectural height in 1885) but also the height of "the level of the lowest, significant, open-air, pedestrian entrance" of the monument. That last height was necessary to fulfill the architectural height standard as set forth by the Council on Tall Buildings and Urban Habitat, the internationally recognized group which set standards for measuring tall building heights.

Full details on the survey, including results, are found in a detailed report on the NGS web site.

Continually Updated Shoreline Product (CUSP)
Shoreline is a dynamic interface between land and water. Over the years, several continuous shorelines were developed, but most have not been maintained and, therefore, they no longer adequately represent changes to a tidally-based datum shoreline. Today, NGS' Continually Updated Shoreline Product (CUSP) is both continuous and frequently revised with the most up-to-date campaign information available. Where applicable, CUSP references a mean high water shoreline based on vertical datum (VDatum) modeling or image interpretation using water level stations and shoreline indicators. CUSP uses state-of-the-art technologies to incorporate both NOAA and non-NOAA contemporary sources (aerial photographs, satellite imagery, lidar, IFSAR, and external shoreline vectors) to generate more accurate shoreline vectors.

The product is available, free of charge, from the NOAA Shoreline Data Explorer application. http://ngs.noaa.gov/NSDE. The site provides information by state on sources, compilation techniques, and other relevant information.

IERS site surveys
A primary objective of the International Earth Rotation & Reference System Service (IERS) is to serve the astronomical, geodetic and geophysical communities by providing realizations of the International Terrestrial Reference System (ITRS). The ITRS is realized by estimates of the coordinates and velocities of a set of stations observed by geodetic techniques comprised of: Very Long Baseline Interferometry (VLBI), Lunar Laser Ranging (LLR), Satellite Laser Ranging (SLR), Global Navigation Satellite Systems (GNSS, including the Global Positioning System, GPS), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS). These realizations of the ITRS, differentiated by epoch date, are each referred to as the International Terrestrial Reference Frame (ITRF).

The current realizations of the geometric reference frames of the NSRS (NAD 83(2011), NAD 83(PA11) and NAD 83(MA11)) all are mathematically defined through their relationship with the ITRS. As such, it is not just important, but mission-critical to NGS for the ITRS to be as accurately realized as possible.

The ITRF realizations are a combination of the 4 separate geodetic techniques, and so it is imperative that very accurate "ties" connect them. A "tie" is a geometric vector between the conventional reference points of technique instruments located in close proximity to one another. Techniques in close proximity to one another are said to be "colocated". Determination of these geometric tie vectors are performed using terrestrial survey techniques (triangulation, trilateration, leveling) in conjunction with GNSS. Such surveys are called "IERS site surveys".

In both the spirit of scientific cooperation as well as the direct accomplishment of its mission, NGS has begun providing the IERS with high precision local tie vector information at colocation sites considered as priorities by that service. Over the last four years, NGS has successfully conducted local tie vector surveys at IERS network sites: Brewster, WA, Washington, DC, Fort Davis, TX and Kauai, HI. Reports detailing these IERS site surveys, along with associated data products, are available at: http://ngs.noaa.gov/corbin/iss/index.shtml

Instructional Videos
NGS recently partnered with the COMET® program to produce 4 short videos collectively titled "An Introduction to Geodetic Datums." A link to these can be found on the NGS home page. The aim of the videos is to provide an understanding of the history of the nation's datums, and of NGS' plans to release new datums in 2022. The videos may be found online at: http://youtube.com/playlist?list=PLsyDl_aqUTdFY6eKURmiCBBk-mP4R10Dx

These videos are part of a broader effort to add to NGS's educational offerings (see the Ten Year Strategic Plan, Goal 3, Objective 5). NGS has dedicated funds to develop additional material with COMET in 2015. The next major project will be a more in-depth look at datums and heights, in the form of on online tutorial.
Topobathy lidar in the Islamorada, Florida Keys Vicinity.

COMET is part of the University Consortium for Atmospheric Research (UCAR), and is a world leader in support of education and training for the environmental sciences.

Topo/Bathy Lidar
In 2013, NGS conducted an extensive evaluation of a new Riegl VQ-820-G topographic-bathymetric ("topo-bathy") lidar system. This system was evaluated to: 1) determine its ability to acquire shallow, nearshore bathymetry with a low-power, narrow-beam topo-bathy system in key areas impacted by Hurricane Sandy, 2) develop the foundation for the Hurricane Sandy bathymetric lidar contract specifications, and 3) provide data to NOAA's Office of Coast Survey for possible use in updating nautical charts in priority areas.

Since NGS' evaluation of the Riegl VQ-820-G topo-bathy lidar system, more than 2,600 square miles has been collected in 2014 through a combination of contract and in-house resources in the near-shore areas impacted by Hurricane Sandy. These mapping efforts were made possible through the Disaster Relief Appropriations Act of 2013 in support of navigation services for coastal states affected by Sandy. This lidar data will be used to update the shoreline and nearshore bathymetry on NOAA nautical charts in Sandy-impacted areas and will also be used by state and federal agencies, as well as academia, for coastal zone planning, emergency response, and resiliency efforts. The topobathy sensors used by Dewberry and NGS for collecting the nearshore bathymetry have the capability of capturing high density data (up to 18 points per square meter) and penetrating to a depth of up to 10 meters where water clarity permits.

To best meet common requirements, help to eliminate duplication efforts, and leverage joint capabilities, NGS has also been striving to coordinate topo-bathy data collection both within NOAA and with other mapping agencies through the Joint Airborne Lidar Bathymetry Technical Center of Expertise (JALBTCX). This year NGS supplied post-Sandy topo-bathy lidar for portions of Barneget Bay, New Jersey to NOAA's Office of Coast Survey to update NOAA Nautical charts and to the NOAA Coastal Services Center for dissemination via Digital Coast. Several other areas in New Jersey will soon be made available. Additional topo-bathy surveys are being conducted in Long Island Sound, the Florida Keys, St. Croix, and Puerto Rico for use by the Coast Survey and NOAA's National Centers for Coastal Ocean Science.

Emergency response enhancements (using geo referenced oblique imagery)
In 2013, after assessing NGS's emergency response surveys for Hurricane Sandy, NGS made it a goal to collect oblique imagery and make the data easily accessible to both the public and emergency responders and coastal managers. NGS began by first designing a new mount for their dual camera Applanix Digital Sensor System (DSSTM) 439 RapidOrthoTM medium format airborne mapping system.

Collecting oblique imagery to photograph a wider area and improve the visibility of vertical structures such as sides of buildings (as opposed to only the tops of buildings as typically seen in traditional imagery collected at nadir) was viewed as a much needed improvement for large scale events such as Sandy. This oblique imagery will provide emergency and coastal managers with the information they need to develop recovery strategies, facilitate search-andrescue efforts, identify hazards to navigation and HAZMAT spills, locate errant vessels, and provide documentation necessary for damage assessment through the comparison of before-and-after imagery.

On the morning of July 4th, 2014, less than 12 hours after Hurricane Arthur roared up the coast of North Carolina and Virginia, NGS was able to collect oblique imagery to document damage, erosion, and potential impacts to navigation. This collection of coastline imagery, now available online (http://storms.ngs.noaa.gov/storms/arthur/oblique/) employs a front end webpage that quickly provides oblique imagery with coordinate attributes for the public and allows downloadable orthoimagery in .tif or georeferenced formats depending on the needs of the user. The georeferenced image has been compressed and tiled to allow the imagery to both load quickly in any GIS software as well as be dragged and dropped into any GIS without having to go through multiple steps to load it. Bulk downloads of all the images collected in one day is also an additional feature for those that may need it.

Calibration Baselines
NGS conducts a cooperative program providing surveyors with a means to detect and correct errors associated with Electronic Distances Measuring Instruments (EDMI). In support of this program NGS has established hundreds of EDMI Calibration Base Lines (CBL) throughout the United States in collaboration with various government agencies, universities, professional societies, and others. The highly accurate linear distances established at CBLs provide a locally accessible standard for evaluating EDMI distance measuring performance.

Recently, NGS has taken steps to update the CBL program, with a goal of making the program more useful to our customers and partners. The NOS NGS-8 "Establishment of Calibration Base Lines" technical document has been revised and is available for download at the NGS CBL website (http://www.ngs.noaa.gov/CBLINES/calibration.html). Revisions include a choice of monument types: traditional ground-level monuments (requiring a tripod), or forced-centering observing piers. Monument spacing has also been revised to accommodate modern EDMI.

NGS is also in the final stages of re-writing CBL data collection and analysis software to a Windows-based format. This new version should be a vast improvement, enabling users to digitally capture data and metadata. The software should be available in late 2014 for download from the NGS CBL website.

Antenna Calibrations
NGS has provided antenna calibration services since 1994, and recently added capability for absolute calibrations to complement the traditional relative calibrations. NGS understands that the surveying community uses a large variety of antenna makes and models, and remains committed to calibrating the antennas used by the surveying community. If you use an antenna which has not been calibrated, please see the Procedures at http://www.ngs.noaa.gov/ANTCAL for information on how you can submit your antennas for free calibration and addition to OPUS.

What you may not know is that the NGS website http://www.ngs.noaa.gov/ANTCAL provides a wealth of information to help surveyors visually identify their antennas. The ANTCAL website contains photos (top and side) for most antennas, as well as engineering drawings with antenna dimensions, and annotations denoting the north orientation feature to use when deploying in the field. Recently, NGS started adding close-up photos of antenna labels as the part number and label often serve as a more unique identifying mark than antenna photos alone.

Dr. Dru Smith has been the Chief Geodesist at NGS since 2005, and most recently led the development of the NGS Ten Year Strategic Plan. During his years at NGS, he has been involved in geoid modeling, ionosphere research and most recently in updating the datum transformation software GEOCON.
Doug Graham earned a Bachelors of Arts degree from University of Maryland, Baltimore County and a Masters degree in Geography from Towson State. Thirty-two years with the National Ocean Service included coastal and airport survey field work, office compilation, review, quality assurance, and development.
Kendall Fancher is Chief of the National Geodetic Survey's Instrumentation & Methodologies Branch. He has 30 years of experience in geodetic observing procedures conducted by the NGS.
Erika Little is the NGS Training Coordinator. She joined NGS as a Presidential Management Fellow from the University of Texas, and has worked on a variety of projects within NGS in the past 13 years.
Christine Gallagher recently became the Constituent Resource Manager at NGS after helping coordinate the National Height Modernization Program for the past five years. She has worked with programs across federal agencies that aim to improve decision-making by using accurate geospatial information, and she previously earned a Masters in Engineering and Public Policy at the University of Maryland.
Gretchen Imahori works in NGS' Remote Sensing Division (RSD) supporting NOAA's Integrated Ocean and Coastal Mapping initiative and integrating RSD's bathymetric lidar data into NOAA's pipeline to update nautical charts. She has a BS in Chemistry from SUNY at Buffalo and a MS in Earth Science with a focus in Ocean Mapping from the University of New Hampshire.
Andria Bilich received the B.S. degree in geophysics from the University of Texas, Austin, in 1999, and the Ph.D. degree in aerospace engineering sciences from the University of Colorado, Boulder, in 2006. Dr. Bilich is a Geodesist with the National Geodetic Survey--Geosciences Research Division. Her research interests include GNSS antenna calibration, GPS multipath characterization, and precision improvements to GNSS positioning for geoscience applications.

A 2.853Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

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