Everest Keep changing its height

1399/09/19 | بخشنامه ها



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The highest point on Earth has a newly announced elevation. Mount Everest is 29,031.69 feet above sea level, according to survey results presented today. That is more than two feet higher than the altitude previously recognized by the government of Nepal.

The elevation, which was announced on December 8 in a joint statement by the Survey Department of Nepal and Chinese authorities, is the culmination of a multiyear project to definitively measure the legendary mountain. As the first serious survey of Everest in 16 years, the effort has been closely followed by the geographic community—particularly scientists analyzing how a devastating 7.8 magnitude earthquake in 2015 affected the region.

Last spring a small group of Nepalese surveyors and guides endured the biting cold of a nighttime ascent, reaching the top at 3 a.m. local time so they could conduct their work unimpeded by crowds of recreational climbers, to try to settle the matter. 

“We want to deliver the message that we can do something with our own [country’s] resources and technical manpower,” Khimlal Gautam, chief survey officer for the project, told National Geographic last year.

Technological peaks

In 1856, mathematician Radhanath Sickdhar found that Everest is the highest mountain in the world while he was working for the Great Trigonometrical Survey, a project dedicated to surveying and mapping the Indian subcontinent. Since then, a handful of surveys have sought to pin down the mountain’s true height with the best technology available at the time.

Until the advent of satellites, surveyors used a device called a theodolite, a precision optical instrument mounted on a tripod, for measuring angles between two designated points. Lugging their heavy equipment from hilltop to hilltop, a survey team would incrementally measure Everest’s height from sea level, zig-zagging north from the Bay of Bengal until they could see the peak.

A 1954 survey using a similar technique calculated that Everest stands at 29,028 feet above sea level, a number that is still recognized by many countries and map publishers.

Then in 1999 a survey led by cartographer and explorer Bradford Washburn, and sponsored by the National Geographic Society, was the first to use GPS technology to measure the Everest summit. That team’s work delivered an altitude of 29,035—the figure still in use by the Society until the new measurements can be fully verified.

Mounting excitement

To make their new survey as complete as possible, the Nepalese team decided to employ both techniques. On May 22, 2019, Gautam summited Everest with four teammates and deployed a GPS receiver, along with ground-penetrating radar to measure the depth of the snow piled on top of the rock. Meanwhile, teams of surveyors waited at eight sites with views of Everest’s summit to fix its elevation at sunrise, when the atmosphere is most clear, with modern laser theodolites.

But after the Survey Department of Nepal completed its field work last year, the project became mired in international politics. During Chinese President Xi Jinping’s state visit to Nepal in October 2019, officials announced that the two countries would cooperate in re-surveying the mountain, delaying the revelation of the new height. A team of Chinese surveyors were at work on the north side of the mountain this spring measuring the summit using China’s network of Beidou satellites, a rival to the GPS system.

Now that the results have been announced, representatives from both countries expressed extreme confidence in the new altitudes. But Gautam is quick to point out that no matter how accurate, every survey comes with some margin for error. “In survey mapping, we can’t find the exact point or altitude,” he says. “We’re trying to find the MPV: most probable value.

Source: National Geographic


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