Many times human beings have surmounted Mount Qomolangma, but the height of the earth's highest peak, known to westerners as Mount Everest, remains an open question.

Thirty years after China's first measurement of its height, more than 20 Chinese surveyors and mountaineers Sunday reached the top of the world in the Himalayas on a mission to give a new, but not necessarily final, answer to a question that has aroused the interest of many: How high on earth is this peak?

In an attempt to provide a benchmark for tracing the mountain's growth, or shrinkage, a key task for this survey mission is to spot, with a radar device, where the rock formation lies under the snow and ice cover on top of the peak, Chen Xianjun, a surveyor with the State Bureau of Surveying and Mapping who participated in the work, told Xinhua.

If successful, the survey expedition will become the first to determine the location of the peak's rock formation with the most advanced technology in the world, he said.

The surveyor said that radar technology can help researchers ascertain the height of the rock formation after subtracting the depth of snow and ice on the top of the peak from the whole.

Italian surveyors used the same radar technology in May 2004, but the researchers so far have not published their work.

Since the snow-capped, pyramid-shaped peak straddling the border between China and Nepal fell on the eyes of modern men, they have been seeking an answer to their question about its height.

A Chinese survey in 1975 found that the peak stands 8,848.13 meters above sea level.

Under the seeming growth of the world's tallest mountain from 8, 840 meters, as measured by a British survey team in India in 1852, to 8,850 meters scaled by American researchers in 1999, lies a controversy over the peak's rise and fall.

Once a benchmark height of the rock formation is decided, it will become easier for researchers to monitor the change of the mountain, Chen said.

Conventional geological theory predicts that Mount Qomolangma, which was formed about 60 million years ago, is growing at a certain speed with the rise of the Himalayans as a result of crustal upthrust, but some researchers in recent years have contended that the summit is becoming smaller as it begins to subside, said Zheng Du, an academician with the Chinese Academy of Sciences (CAS).

There is also warning that the summit of the earth is shrinking as a result of melting glaciers, caused by global warming.

According to observations by CAS academician Chen Junyong and other scientists, the height of Mount Qomolangma with the rock formation and its snow and ice cap as a whole dropped 1.3 meters from 8,849.75 meters in 1966 to 8,848.45 meters in 1999.

It is an accepted rule that the measurement of the height of a mountain can contain the snow and ice cap, but a precise measurement on its rock formation is favorable for monitoring the change of its height, Chen said.

A reliable benchmark, however, was something hard to get in the past because of lack of proper survey methods or advanced equipment.

A woman mountaineer in the 1975 expedition of China inserted a metal stick into the snow to measure its depth, which turned to be 920 millimeters. But even researchers who participated in the 1975 measurement said this method could not get scientific results given the strength of an individual and the angel from which the stick was inserted.

A steel bar was used in the survey by an Italian research team in 1992, which showed the snow and ice cap was 2.55 meters deep, but the question of how deep the steel bar could pierce through, dependent on human strength, remained, CAS academician Zheng Du said.

Chen Xianjun said that the radar technology is one of innovative methods in this year's survey mission and he hopes can lead to a breakthrough in the survey of the earth's summit.

The surveyor said that the global positioning system, or GPS, is also being used in the current survey to ensure a precise result, said Chen.

The traditional trigonometric leveling method, which was used in the 1975 expedition, is still being used in this mission for comparison.

Researchers will also leave a nail, less than 10 millimeters in diameter, on the rock at 8,300 meters for future GPS monitoring.

The survey endeavor is part of a comprehensive scientific research program on the peak, which was launched in March.

Scientists will also collect data for studies on the changes of the eco-system and the atmospheric environment in the Qomolangma area, the shrinkage of glaciers, and meteorological change.