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# Height Modernization

NOAA's National Geodetic Survey employees level to a pier as part of a larger island-wide project to provide St. Thomas, U.S. Virgin Islands with a vertical datum.  The National Geodetic Survey, in cooperation with the surveying community, is working to develop and test more effective ways to improve elevation data. 

Sea level rise, subsidence, earthquakes, and even oil and gas extraction, can all cause the elevation of an area to change. State and local governments can spend tens of millions of dollars each year adjusting engineering projects such as roads and buildings that are affected by these shifting surfaces. Enter the need to determine elevations better, faster, and cheaper—and enter Height Modernization.

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## GPS fueled

Appearing on the scene in the 1980s, GPS revolutionized surveying. However, the vertical accuracy of GPS measurements (elevations) has not been as good as the horizontal accuracy (latitude and longitude). To address the problem, the National Geodetic Survey developed the Height Modernization program. "Height Mod" identifies standards, specifications, and techniques for using the Global Positioning System to obtain accurate elevation measurements. Sounds easy, right?

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## Testing the process

Although faster and cheaper than traditional survey methods for determining elevations, implementation of Height Modernization is still evolving. The National Geodetic Survey, in cooperation with the surveying community, is working to develop and test more effective ways to improve elevation data. As standards and techniques are developed, more states can adopt and reap the benefits of Height Modernization.

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## If it's better, why isn't everyone using it?

Height Modernization techniques are not yet widely practiced by the surveying community. A major effort known as "technology transfer" is currently underway to introduce these techniques and foster their widespread use around the nation. In addition, the existing geodetic reference framework that supports height measurements is outdated in many locations and must be modernized. The National Geodetic Survey is working to enhance the existing framework with a newer, smaller network designed to support and utilize the technological advances of the Global Positioning System.

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## Aircraft aid

When your plane is approaching the airport runway, wouldn't you like to know that the pilot knows exactly where the ground is? Reliable elevation data can be collected in real time because of Height Modernization. With accurate heights measured at the airport through Height Modernization techniques, approach-and-landing procedures are safer. How's that for peace of mind?

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## Recovering from disasters

In the aftermath of disasters such as hurricanes and earthquakes, time is of the essence in reestablishing water and electricity infrastructure and reopening damaged roadways and bridges. By allowing elevations to be determined quickly using GPS, Height Modernization improves disaster preparedness and recovery and infrastructure projects. GPS is especially useful when local infrastructure has been largely destroyed; when a construction, public works, or transportation project involves large-scale coverage; and when difficult, rugged terrain lies between survey points.

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## Water runs downhill

Water runs downhill, right? Well, because our Earth's surface is constantly changing, the direction of "downhill" is changing as well. Because Height Modernization precisely pinpoints the rise and fall of land surfaces, it helps us understand which direction water will flow. This knowledge increases the efficiency of water delivery and drainage systems and helps reduce urban and agricultural runoff and water pollution. For the same reason, Height Modernization allows more precise modeling of storm-surge and pollution trajectories during extreme weather and hazardous spill events, even in very flat terrain.

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## Saving time and money

In economic terms, a state-of-the-art National Spatial Reference System, which includes elevation data, saves state and local governments vast sums of money. It replaces expensive, labor-intensive field surveying projects (including flood-plain and other mapping activities) with new, more timely and cost-efficient Global Positioning System technology. It reduces engineering errors and disasters caused by land surfaces changing due to subsidence, movements of the Earth's crust, floods, earthquakes, and other natural phenomena. The time and money saved by Height Modernization means that, all in all, it's a pretty good investment.

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###### More **Information**

          - National Geodetic Survey
          -  Height Modernization
          -  National Spatial Reference System Primer
          - Global Positioning
          - Height Modernization Facts (PDF)
          - Geodesy Discovery Kit (For Kids)
          - National Water Level Observation Network

Did you know?

				The National Spatial Reference System (NSRS) is a consistent coordinate system that defines latitude, longitude, height, scale, gravity, and orientation throughout the United States.

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