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Nepal and China officially announced the new height of Mt Everest after both countries recently measured the world’s tallest mountain. The new height is 8848.86 metres.



This will be the first time the two countries that the mountain straddles are announcing the height, ending controversies regarding its height since it was first measured in 1849 by the British.

Between 1849 and 1855, observations were made from Dehradun, India base to Sonakhoda base in Bihar. During these triangulation observations, the Himalayan peaks of Nepal were also observed. At that time it was not known that this peak in the Himalayas is the highest in the world.

During computations, the mean computed height of ‘Peak XV’ came out to be 29,002 ft and it was named after Sir George Everest, the ex surveyor general of India.

The widely accepted height of 8,848 metres or 29,028 feet was determined by the Survey of India in 1954 from Bihar using the trigonometric method. It was the third survey by India.

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 workon 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: https://www.nationalgeographic.com/s...ina-and-nepal/

https://youtu.be/PvF8FNtt62Q

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This is a geo-political signal more than anything else. China wants to hint to India that Nepal and them are working closely on all matters.

[ruzbehxyz]

Recently, China and Nepal announced that Mount Everest is 86 cm taller than the 8,848 m accepted globally so far. So, how is original height calculated and what does the revision mean, we take a look.




The first recorded attempt at measuring the Everest using modern calculations had come in 1856, when surveyors commissioned by the then Surveyor General of India George Everest estimated its height at 29,002 feet. Without going into the sines and cosines of the craft, suffice it to say that using accurate measures of distance and multiple readings of angles from different positions, it is possible to use trigonometry to determine the elevation of any feature. A key instrument in this exercise is the theodolite, which helps in measuring angles. It is much like an instrument you may have observed engineers use in road building. As it turned out, the height determined by officials of the British Raj was quite close to the one Indian officials would compute in the 1950s using more modern instruments: 29,028 feet, or 8,848 metres. It is still the most cited figure for Everest's height.



NOW, EXPERTS ARRIVE AT HEIGHTS USING GPS
The key tool employed by Chinese and Nepalese surveyors was a GPS receiver, which was carried to the top of Everest. The factor of time taken for signals to travel from the receiver to multiple satellites and the distance of these satellites from fixed objects provides a highly accurate approximation of the location and elevation of the peak.

170 years ago, Everest's crew, led by mathematician Radhanath Sikdar, solved the problem of sea level by actually working their way up from the Bay of Bengal by employing a network of line-of sight stations until Everest itself was visible and could be measured using trigonometric formulae.
Another factor that proves contentious is whether to calculate the depth of the snow on a mountain peak as part of its height. The Nepalese surveyors used a ground-penetrating radar to actually measure the height of the snow standing on top of Everest's rocky crest but in the past it has been debated whether the snow should be part of the calculation.





HOW SEA LEVEL IS MEASURED
To accurately determine sea level while interpreting GPS data, scientists now rely on two models that conceptualise the shape of the Earth: ellipsoid, which presents the Earth's surface as smooth and uniform and is used to measure geographical coordinates; and geoid: a model that takes into account gravity and how it impacts sea levels and how the rotating Earth bulges at the Equator and flattens at the poles. The geoid model is a close proxy for mean sea level. Calculations involving the ellipsoid and geoid heights finally give the orthometric height, or the height above sea level.


Source: National Geographic, NOAA, Slate, media reports.

Source link: https://m.timesofindia.com/india/how...m_campaign=TOI