葫芦娃视频

At 14,001 feet, Colorado鈥檚 Sunshine Peak is barely a 鈥�14er鈥� 鈥� and might not be one for long. The status of Huron Peak, 14,003 feet, is also in jeopardy.

In fact, all of Colorado is expected to lose about two feet of elevation. Seattle will lose three feet. Florida will stay about the same.

Blame it all on better science.

For the last five years, U.S. government scientists have been redefining elevation 鈥� height above an agreed upon reference point 鈥� using a new method that involves satellites and airborne gravity-measuring machines to determine a new baseline for measuring the heights of landmasses. Basically, they鈥檙e establishing a new 鈥渮ero.鈥�

Once complete, in 2022, the decade-long project will provide the most precise measurements ever.

The revised elevation data will help organizations like FEMA determine more exact U.S. flood plains, for example, according to Derek van Westrum听(PhDPhys鈥�98), a scientist with NOAA鈥檚 National Geodetic Survey (NGS), which sets federal standards for surveying and mapping activities. The updates will aid land surveyors, oceanographers and geographers also.听

鈥淢easurement uncertainties will be within centimeters now instead of feet,鈥� said van Westrum, who works for NOAA in 葫芦娃视频 and is responsible for the survey鈥檚 terrestrial gravity measurements. 鈥淚n Seattle right now, if you wade into the ocean, the current height system will indicate you鈥檙e about three feet above sea level.鈥�

NOAA is the National Oceanic and Atmospheric Administration. Current official elevations date from the 1980s.

The new measurement system is a far cry from the old way of doing things: For hundreds of years, terrestrial elevations were measured by hand from sea level using rulers, levels and brass markers.

While largely accurate when done correctly, this method is extremely tedious and costly, said van Westrum. And in places like Colorado, rugged terrain and extreme distance above sea level make it difficult to precisely measure. In Alaska, it鈥檚 nearly impossible. It鈥檚 an easier task in flat, seaside states like Florida.

鈥淭he new system can cover the entire continent quickly, and also keep it up to date as the Earth slowly changes, something you can't easily do with an army of folks with rulers,鈥� van Westrum said.

The new survey method also improves upon GPS-based elevation mapping, which assumes a simple ellipsoid model of Earth. In contrast, the new method accounts for the complex and evolving shape of the planet.

鈥淧eople know the Earth is round, but because it鈥檚 spinning, it kind of blobs out into an ellipsoid,鈥� van Westrum said. 鈥淎nd with mountains and valleys and things like that, we know the Earth isn鈥檛 a perfect ellipsoid. It looks more like a lumpy potato.鈥�

Scientists on the project, called GRAV-D, short for Gravity for the Redefinition of the American Vertical Datum, measure gravity鈥檚 pull near the Earth鈥檚 surface. They use the data to create a model of Earth鈥檚 geoid 鈥� a mathematically derived approximation of global mean sea level.

Measuring distance from this global mean to the top of landmasses will yield new, highly accurate elevations.

In order to map Earth鈥檚 lumpy potato shape, NGS uses gravity meters developed by Tim Niebauer鈥檚 (PhDPhys鈥�87) company, Micro-g LaCoste in Lafayette, Colo., in addition to NASA satellites that collect gravity-related data.

Niebauer鈥檚 machines, which range in size from small toasters to barrels, use mirrors and lasers to measure gravity, said van Westrum, a self-described 鈥済ravity guy鈥� who worked at Niebauer鈥檚 company for 15 years before joining the NOAA survey. Scientists deploy the machines on slow-moving GRAV-D aircraft and on the ground.

鈥淵ou鈥檙e getting a picture of the Earth from outside of the Earth,鈥� said Niebauer, who commercialized his gravity meters after perfecting them at CU鈥檚 JILA, a joint institute of the university and the National Institute of Standards and Technology (NIST).

To ensure that GRAV-D is as precise as possible, survey scientists have undertaken parallel projects across the U.S. using both old and new measurement systems and comparing results. Van Westrum led a Colorado project that measured elevations between Durango and Walsenburg, for instance. Initial data shows similar results from the two methods.

GRAV-D still has five years to go before it becomes the new standard for measuring elevation. Once it鈥檚 in effect, in 2022, a NOAA team will continually monitor agents of geologic change 鈥� such as volcanic eruptions, earthquakes and the movement of tectonic plates 鈥� all of which influence Earth鈥檚 dynamic shape. As the shape changes, so will global mean sea level and the elevations of landforms.

鈥淵ou鈥檒l be able to go anywhere with a GPS and know exactly where you are, latitude, longitude and how far above the surface of the geoid you are,鈥� said van Westrum.

While it鈥檚 possible that some places could gain elevation, in general they鈥檒l lose it, van Westrum said 鈥� imperiling Colorado鈥檚 shortest 14ers. Like poor Sunshine Peak.
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Opening illustration by Tim O'Brien
Photo by National Oceanic and Atmospheric Administration/Department of Commerce
Illustrations by NASA/JPL/University of Texas Center for Space Research

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