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Science

Height Matters

A team of Chinese mountaineers and surveyors were the only climbers to stand on top of the world in 2020 - their mission to calculate the height of Mount Qomolangma

By NewsChina Updated Aug.1

Sixty years after the first ascent of the tallest mountain in the world by a Chinese team in 1960, a team of climbers and surveyors stood unexpectedly alone at the peak in an unusual climbing season curtailed by the coronavirus pandemic. 

The group had a motive other than commemorating the earlier climb. Setting off on their third attempt on May 24 after having been beaten back by the weather on two occasions, the team clambered to the top of the world on May 27 at 11am and immediately got to work - making a new measurement of the height in an attempt to resolve a vexing question.  

On May 6, the base camp on the Tibetan side of Mount Qomolangma, otherwise known as Mount Everest, at 5,200 meters above sea level, saw good weather with high visibility. The snow on the summit was clearly visible. Yuan Fudong stuffed his sleeping bag into his backpack, and along with the other 30 team members, all dressed in red mountaineering gear, gathered for a simple ceremony at 1pm before setting off toward the next camp.  

The team, composed of professional climbers from the China Mountaineering Team and surveyors from the Ministry of Natural Resources (MNR), climbing in a season when all other attempts on the world’s highest peak had been halted due to the Covid-19 pandemic, had a specific goal. Its mission was to accurately remeasure the height of the mountain using state-of-the-art equipment, including the Global Navigation Satellite System (GNSS), a gravimeter, which measures differences in gravity from place to place, snow depth radar, meteorological measuring instruments and surveyor’s beacons. 

The weather forecast for May indicated three good weather windows that could allow an attempt on the summit. Departing on May6, the team aimed to meet the window on May 12, but a change in the weather caused the attempt to be abandoned. They tried again on May 16, aiming to summit on May 22, but bad weather due to Cyclone Amphan derailed this attempt. On both occasions, teams laying ropes on the upper slopes were forced back to base camp.  

Conflicting Measurements
Straddling the China-Nepal border, Mount Qomolangma’s height is globally recognized as 8,848 meters. Called Sagarmatha in Nepal, the first attempt to measure the mountain was in 1852 by Indian mathematician and surveyor Radhanath Sikdar, who put the height at 8,840 meters, his calculation announced in 1856 by the then-British colonial government. The current height of 8,848 meters was established first by another Indian survey in 1955, and then confirmed by a Chinese team which summited in 1975, who measured the height as 8,848.13 meters above sea level. Currently, Nepal recognizes the 8,848 height. In 2005, the former Chinese State Bureau of Survey and Mapping sent a team of 24 to measure the height. Excluding the snowpack, the new height was announced as 8,844.43 meters, however this height was not recognized by Nepalese authorities at the time. Other international teams have attempted to measure the elevation, all with differing results, none of which have been officially recognized. These include a US team in 1999 which measured the mountain at 8,850 meters, and an Italian team in 1992 which gave a height of 8,846 meters.  

“There are two main reasons why we’re remeasuring. One is due to the changing height of Mount Qomolangma and the second is modern measuring technologies, which significantly improve accuracy,”Dang Yamin, a researcher at the Chinese Academy of Surveying and Mapping and head of the survey team told NewsChina in mid-May. 

Basically, the mountain, which is in a tectonically active zone, sinks due to major earthquakes, and rises in between. Due to plate tectonics, the Indian Plate is still pushing northward into the Eurasian Plate, a collision which created the Himalayan Range and the Qinghai-Tibet Plateau. This means Mount Qomolangma is rising 4.4 millimeters per year, an increase of 4 centimeters each decade, or 13 centimeters in 30 years. If the margin of error when measuring the peak is about 10 centimeters, then the height should be measured every 20 to 30 years, Dang said.  

Earthquakes have the opposite effect. A magnitude 8.0 earthquake in 1934 struck Nepal, with the epicenter only 9.5 kilometers from Mount Qomolangma. The summit lost 63 centimeters. The epicenter of the April 2015 8.1-magnitude earthquake in Nepal was 200 kilometers from the mountain and it is thought to have knocked a few centimeters off the height. Some researchers used satellite remote sensing data to study the height of summit, which indicates a possible decrease, but this method is relatively imprecise. An accurate measurement requires geodetic observation.  

As well as the height, Dang said the mission intends to gather data on tectonic plate motion and the influence of earthquakes on Mount Qomolangma in the Qinghai-Tibet region. Accurate data such as peak snow depth, meteorology, wind speeds and glacier monitoring can further provide first-hand information for natural resources monitoring and ecological environment protection in and around the neighboring region.  

Global Disagreement
There is still no international agreement on the height of Mount Qomolangma. Geologists disagree on how to calculate mountain heights. There are questions over whether to take the height from the snowpack, or from the actual bedrock. Nepal chose to calculate the top based on the snow cover. There are two routes to climb Qomolangma, from the northern Chinese side or the southern route in Nepal. The south face route is more established commercially, and Nepalese mountain authorities give more permits. In 2019, the Nepalese government issued 381 permits, with each providing US$11,000 in revenue for Nepal, as well as tens of thousands of dollars paid to mountain expedition companies and their staff. According to a 2018 New York Times article, the lower height recognized by China persuaded many climbers to opt for the Nepal route. “Having those few extra feet recognized on summit certificates was enough for some mountaineers to switch routes, opting to climb from, and spend money in, Nepal,” the article said.  

In 2017, Nepal announced it would conduct its own survey, sending teams in 2017 and 2018, which would use a combination of traditional and modern methods. The Nepali spokesperson for the survey department told the BBC in May that it has almost finished collating the data, and was preparing to go public with the result, however the pandemic has delayed the process. In October 2019, a joint statement released after Chinese President Xi Jinping visited Nepal stated that the two countries would “jointly release the height and conduct scientific research.”
 
In 2005, China took its measurement from the rock surface. “There is significant error if you measure the height of the snowpack due to the change in different seasons throughout a year. The wind can blow away the top layer, the sun can melt it, so it means you get different measurements at different times. It’s hard to say who’s right and who’s wrong,” Dang said. “The rock surface height changes only four millimeters per year. If we measure every five years, the height difference should be two centimeters maximum. But if the difference is higher, it means one of the two measurements is wrong.” 

Dangerous Journey
The journey to the summit of Mount Qomolangma is dangerous, and the organizers invested huge manpower, material resources and financial resources into the effort.  

Addressing why modern technologies such as satellite remote sensing images or GPS positioning systems that are widely available cannot be used to directly measure the height, Dang said that satellite remote sensing images are mainly used for surface detection. Heights can only be measured with a margin of error of two meters, and only from the top of the snowpack.  

Other ways to measure the mountain have been discounted as being too dangerous or unfeasible, such as measuring by aircraft or drone, due to operating limitations and the harsh conditions above a peak over 8,000 meters. It is felt that the most accurate measurement can only result from sending a team to the peak.  

There are two main methods of height measurement. The first is by using triangulation where correcting for gravity, atmosphere and other aspects allows a height to be obtained. The second method is through GPS satellite geodesy, initially used in 2005, but this requires someone to place a GPS receiver at the summit. 

The 2020 expedition is using GNSS satellite survey, precision leveling, photoelectric ranging, snow-deep radar measurement, gravity measurement, astronomical measurement, satellite remote sensing, quasi-geoid refinement and other traditional and modern mapping technologies. Using China-made equipment has been a breakthrough this time. “In addition to aerial gravimetry, the rest is still based on technologies adopted in 2005, but this time we used a lot of domestic equipment,” Dang said.  

GNSS satellite measurements consist of four systems: BeiDou (China), GPS (US), GLONASS (Russia), and Galileo (EU). “In 2005, GNSS satellite measurements relied mostly on GPS. This year, we will refer to the four global navigation satellite systems concurrently and mainly depend on data from the BeiDou Satellite Navigation System,” said Li Guopeng, head of the first Geodetic Surveying Brigade under the Ministry of Natural Resources, at a press briefing before the project launched.  

Another innovation is the first use of aerial gravimetry for the measurement attempt. Dang said that the accuracy of the measurements could be about 30 to 40 percent higher.  

“The height we see when we look at it is not its true height,” Zhang Yanping, leader of the 2005 survey team said during an earlier interview with the People’s Daily. “Because the earth is elliptical, and the starting point of your sight is the point at your feet, not the point at the foot of Mount Qomolangma, so you see the summit as lower than its true height.” Therefore, the prerequisite for precise measuring of the elevation of Qomolangma is to find the zero elevation point at the foot of the mountain. 

China takes the average sea surface of the Yellow Sea at Qingdao tidal station in East China’s Shandong Province as the zero elevation point. “One can imagine a sea level, which is a curved surface, with all the gravity values equal on the surface. This is the zero elevation starting surface. There is a gravity value on the surface where the zero elevation point at Qingdao is located. The same gravity value below Mount Qomolangma, once found, could be taken as the starting surface then,” Dang said, adding that it would be more accurate.  

Despite the significant advantages of aerial measurements, it is difficult for an aircraft which would take the measurements to operate safely that high. It is more suitable for low altitude areas.  

“The peak is over 8,800 meters, and the aircraft is flying at an altitude of 200 meters above it, which is very dangerous. The north face of Mount Qomolangma is complex in terrain, with an unstable climate. Experienced pilots pointed out the dangers of attempting it, which might even cause the aircraft to crash,” Dang said. 

After the proposal was rejected, Dang’s team did not give up. As they learned later that the China Center for Aerial Geophysical Prospecting and Remote Sensing of Natural Resources would be able to complete the task, they worked on a detailed technical plan for six months. After it was reviewed by experts, it was included in the overall project plan for the measurement.  

There is only one month a year in which there is a weather window to climb Mount Qomolangma. As summiting the mountain becomes more popular, this is why we see pictures of people stuck in “traffic jams” as occurred last year on the Nepalese side. Eleven climbers died in 2019, with much of the blame pointed at inexperienced climbers and companies eager to make money.  

The Chinese survey team did not want to take a chance on the weather for this attempt even though unexpectedly they found themselves alone on the mountain. The Meteorological Bureau of the Tibet Autonomous Region set up a 16-strong meteorological support team divided into two support service groups to provide meteorological detection and weather forecasts.  

In order to ensure communication, the Tibet Autonomous Region Communications Administration organized China Mobile Tibet Branch to implement the “5G on Mount Qomolangma” plan. Netizens were able to watch real-time video transmissions from the base camp and the moment the surveyors reached the peak and started their measurements. Transporting eight tons of network construction equipment and life support materials by yak, five 5G base stations were built at the 5,300 meter base camp, the 5,800 meter transition camp and at the 6,500 meter advance camp, providing gigabit broadband and special line access. Furthermore, three 4G base stations were built along the route. Specialist staff was stationed at the high altitude camps to ensure the network operated smoothly with reliable data transmission. Data obtained would be sent back to the Geodetic Data Processing Center of the Ministry of Natural Resources in Xi’an in real time.  

When the team of eight climbers finally reached the summit, they had to work quickly. They finished the positioning of the equipment and other observations within two hours. But the result will not come immediately. It is expected that the final height will be released in two or three months. “We still need to be patient and wait for the final result,” said Dang.

Surveyors from China’s Ministry of Natural Resources pose for a photo at Mount Qomolangma base camp, Tibet Autonomous Region, April 14, 2020

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