National Geodetic Survey 

NOAA’s National Geodetic Survey (NGS) provides 

the framework for all positioning activities in the 

Nation. The foundational elements of latitude, 

longitude, elevation, and shoreline information 

impact a wide range of important activities. NGS’ 

mission is to define, maintain and provide access to 

the National Spatial Reference System to meet our 

nation's economic, social, and environmental needs. 

Included below are six highlighted scientific projects 

by NGS researchers and their partners.

Understanding the Role of Human-induced Subsidence in 

Affecting Sea-level Rise Hotspots in the Chesapeake B

The Chesapeake Bay is experiencing 

some very high rates of local sea-level 

rise (up to 4.8 mm/yr), and the rates are 

variable throughout the region. 

Presumably, these variations are due to 

differences in local vertical land motion 

(VLM), with subsidence being a leading 

cause. Unfortunately, we do not have a 

good handle on the spatial variations in

VLM, and the last authoritative study 

was published back in the early 1970’s. 

In 2019, a coalition of scientists from 

Federal, academic and state institutions 

began a 5-year research project attempt 

to tease out a VLM signal across the 

entire Chesapeake Bay area using annual 

GPS measurements spanning from the mouth of the Bay to Delaware Bay, from the coastal barrier islands of 

Assateague to the Shenandoah Mountains.

FY20 Accomplishment(s): From October 5-20, 2019 (FY20), NGS, along with its collaborators, 

successfully obtained an average of 66 hrs of GPS data across 54 sites; the data and metadata have been 

published at https://www.unavco.org/data/doi/10.7283/M6D3-T837. 

Press Release URLs:

https://www.ngs.noaa.gov/web/news/chesapeake-bay-sea-level.shtml

https://www.usgs.gov/centers/cba/science/new-crowd-sourcing-will-contribute-study-land-subsidence-and-sealevel-rise?qt-science_center_objects=0#qt-science_center_objects

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Map showing locations of bench marks monitored as part of the 

Chesapeake Bay Regional VLM Project (left). GPS monitoring on 

Assateague Island National Seashore (right). 
Understanding and Estimating Total Propagated 

Uncertainty for NGS lidar sensors 

Starting in 2016, National Geodetic Survey (NGS) began research efforts with Oregon State University (OSU) 

and the Center for Coastal and Ocean Mapping/Joint Hydrographic Center, University of New Hampshire 

(CCOM/JHC, UNH) toward the development of robust total propagated uncertainty (TPU) models. These TPU 

models cover the range of NGS and Joint Airborne Lidar Bathymetry Technical Center of Expertise 

(JALBTCX) topo-bathy lidar systems and facilitates operational use of topo-bathy lidar in the lidar community 

and Coast survey by providing a level of uncertainty (via cBLUE app shown below) to improve informative 

decisions based on the multi-use of the data. In turn, this aids NOAA in obtaining survey data in challenging, 

nearshore areas, including shoreward of the navigation area limit line (NALL). Additionally, the enhanced use 

of topo-bathy data will contribute directly to NOAA’s Integrated Ocean and Coastal Mapping (IOCM) 

initiatives, by providing data that can simultaneously support coastal science and coastal zone management 

needs.

FY20 Accomplishment(s): Incorporated research to create cBLUE, first phase of testing complete and 

now in use operationally at NGS for Riegl VQ-880-G topo-bathy lidar surveys.

Peer reviewed journal article: Eren et al. 2019 Photogrammic Engineering and Remote Sensing

https://www.ingentaconnect.com/content/asprs/pers/2019/00000085/00000008/

art00011;jsessionid=i5midxo2i62m.x-ic-live-01

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cBLUEApp Module (top right) was created using topo-bathy lidar (middle image) TPU model research (schematic on 

top left) by Oregon State University (OSU) and the Center for Coastal and Ocean Mapping/Joint Hydrographic Center, 

University of New Hampshire (CCOM/JHC, UNH) for use by NGS. 
Applying New Research and Automating 

Satellite-Derived Bathymetry

Starting in 2016, National Geodetic Survey (NGS) began collaboration efforts between the National Centers for 

Coastal Ocean Science (NCCOS) and the Office of Coast Survey (OCS) to create a user friendly Satellite 

Derived Bathymetry (SDB) tool that would provide consistent and quick results utilizing new research from Dr. 

Isabel Cabellero and Dr. Richard Stumpf. Since 2016, progress has been made to incorporate “a robust 

atmospheric correction, a multi-scene compositing method to reduce the impact of turbidity and a switching 

model to improve mapping in shallow water” to improve Dr. Stumpf, et al.’s 2003 SDB algorithm. In tandem to 

this effort, NGS has been working with NCCOS to develop a framework and began developing the NOAA 

SatBathy tool.

FY20 Accomplishment(s): NGS began creating the framework and creation of the SatBathy tool.

Peer reviewed journal article: Caballero & Stumpf 2020 Remote Sensing:

https://www.mdpi.com/2072-4292/12/3/451

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Oregon SDB created Inlet (Oct 2020) using NGS’ new pre-alpha SatBathy tool v1.0 based on research from NCCOS. 
The Experimental Geoid 2020

Starting in 2014, the 

National Geodetic Survey 

(NGS) began publishing a 

series of experimental 

geoid models annually. 

These models contain the 

gravity data from the latest 

satellite gravity models, the 

terrestrial gravity and most 

importantly, the airborne 

gravity from the Gravity for 

the Redefinition of the 

American Vertical Datum 

(GRAV-D) project. These 

experimental geoids have 

been developed to 

demonstrate the geoid 

improvements provided by 

the addition of GRAV-D 

data and by refining the 

geoid computation 

methods. The experimental 

geoid models provide a preliminary but increasingly-accurate view of the changes expected from the upcoming 

North American-Pacific Geopotential Datum of 2022 (NAPGD2022). The experimental geoid 2020 is the first 

model computed jointly by scientists at NGS, the Canadian Geodetic Survey, and the National Institute of 

Statistics and Geography in Mexico.

FY20 Accomplishment(s): NOAA worked with the Canadian Geodetic Survey and the National 

Institute of Statistics and Geography in Mexico to combine gravity data sets, to make the best geoid 

possible for North America, Hawaii, the Caribbean, Central America, and beyond.

Project URL:

https://beta.ngs.noaa.gov/GEOID/xGEOID20/

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Display of the Experimental Geoid 2020 (xGEOID 2020). Image credit: NGS, NOAA. 
Geoid Determination in Mountainous Terrain

In a few years, NOAA NOS will modernize the nation's height system. Instead of measuring heights inland 

from a "mean sea level," heights will be measured relative to a constant geopotential surface known as the 

"geoid," a model of the shape of the Earth under the influence of its gravity and rotation. By providing the shape 

of this undulating surface everywhere, the new system allows surveyors to use GPS receivers to determine 

precise heights anywhere. In the Journal of Geodesy, NGS describes a ground-truth test of the geoid-based 

system in Colorado, demonstrating that it has a relative accuracy of better than 5 cm in mountainous terrain—a 

worst case scenario for geoid determination. When combined with earlier Texas and Iowa surveys (which 

demonstrated better than 2 cm accuracy in smoother terrain), these results indicate the new national height 

system will provide accurate elevations everywhere, with approximately 10X better accuracy. 

FY20 Accomplishment(s): Peer reviewed article published in the Journal of Geodesy demonstrating 

the relative accuracy of the ground truth techniques and various experimental models.

Peer reviewed journal article: van Westrum et al. 2021 Journal of Geodesy:

https://link.springer.com/article/10.1007/s00190-020-01463-8

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Ground truth surveys along US160 in southern Colorado. Setting up a geodetic GPS antenna for horizontal positioning 
Total Station Astrogeodetic Control System (TSACS)

The National Geodetic Survey developed the Total Station Astrogeodetic Control System (TSACS), a system 

for measuring the direction of gravity with astronomical observations. The TSACS directs a robotic total station 

to measure the deflection of the vertical (DOV) by imaging stars. The deflection of the vertical indicates how 

much the direction of gravity has been shifted by local mass anomalies, like mountains. As DOV defines which 

way is up, measuring it in the field will be crucial for verifying the level surface that will define NGS's future 

geopotential height system. The TSACS will also find use in establishing precise orientations and bridging 

classical and modern geodetic observations. Its automated observation sequence can measure deflections of the 

vertical to better than ±0.2 arcseconds in as little as 15 minutes.

FY20 Accomplishment(s): Developed and tested a system for measuring deflections of the vertical by 

imaging stars with a robotic total station.

Project Presentation URL:

https://www.ngs.noaa.gov/web/science_edu/presentations_library/files/aguf2020_-_ryan_hardy.pdf

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The Total Station Astrogeodetic Control System (TSACS) being tested with with a Leica TS60 robotic total station in 

Silver Spring, Maryland. The various components can be viewed using the URL below.