8848.86 meters - in December 8th, President Xi Jinping and Nepal President Bhandari exchanged letters with each other to announce the elevation of the Mount Qomolangma. As we all know, the core of the elevation survey of Mt. Everest is to accurately measure the height of Mt. Everest, which is also a comprehensive surveying and mapping project representing the development level of national surveying and Mapping Science and technology. Since the founding of the people's Republic of China, the elevation survey of Mt. Everest in China has experienced a transformation from traditional geodetic technology to comprehensive modern geodetic technology. Every survey of Mt. Everest reflects the continuous progress of Surveying and mapping technology in China, and shows the highest level of Surveying and mapping technology in China. In 2020, the elevation survey of Mt. Qomolangma has comprehensively applied a variety of technical means, including GNSS satellite survey, snow and ice detection radar survey, gravity measurement, satellite remote sensing, quasi geoid refinement and other traditional and modern surveying technologies. In 2005, the GNSS satellite survey mainly relies on GPS system, while this year's Mt. Everest elevation survey will refer to the four global navigation satellite systems of the United States, Galileo of Europe, GLONASS of Russia and Beidou of China, with the data of Beidou as the main data. < / P > < p > < p > < p > < p > in addition, the airborne gravity survey technology was used to improve the measurement accuracy. It is also the first time for human beings to carry out gravity survey at the top of Mount Everest. It is particularly worth mentioning that the domestic Beidou satellite positioning receiver, peak gravity meter, snow depth radar, Airborne Gravimeter and other core equipment used in this mission are all independently developed by China. < p > < p > < p > < p > < p > on May 27, 2020, the Mt. Everest elevation survey mountaineering team once again stood on the top of the earth. After the summit survey, it is another difficult problem to process the observed data. < / P > < p > < p > < p > < p > from massive data to 8848.86 meters, what are the "problem-solving" steps? < p > < p > < p > < p > < p > < p > "the Everest region is one of the regions with the most severe crustal movement in the world due to its high altitude, extremely cold and anoxic conditions. Therefore, it is a very challenging, extremely complex and difficult comprehensive work to obtain the accurate elevation of Mt. Everest." Guo Chunxi, director of the geodetic data processing center of the Ministry of natural resources, said that it was the third time that he had participated in the calculation of the height of Mount Everest. Guo Chunxi said that since last year, the center has continued to carry out technical research and tackling key problems, and completed relevant data processing scheme preparation, data model establishment, software programming test, data comparison analysis and verification. Guo Chunxi said that compared with the height survey of Mt. Everest in 2005, the difficulty of data processing is that there are more types of data and larger amount of data. "For example, more than 10000 square kilometers of airborne gravity survey was carried out at the peak this year. Previously, GNSS satellite survey mainly relied on GPS. This year, we also refer to the four global navigation satellite systems, namely, GPS of the United States, Galileo of Europe, GLONASS of Russia and Beidou of China, and the data of Beidou are mainly used." How much data is processed by < / P > < p > < p > < p >? Guo Chunxi confessed that this cannot be accurately accounted for. He gave an example: "in order to accurately measure the position of the peak of Mt. Everest, we collect the data of the reference station every 1 second, and the data of each base station contains the data of more than 50 navigation satellites. Imagine that there are 86400 seconds in a day. In addition, we have a large number of base station observation data. This data is huge only He said that since April 2019, a large number of existing elevation, GNSS and gravity data of Mount Everest have been collected, and preliminary sorting and analysis have been carried out to prepare for the follow-up work. Since then, we will transfer the data of Mt. Qomolangma and the gravity data of more than 3 months, including the gravity data of Mt. Everest and the gravity level of more than 3 months And so on. " Guo Chunxi said. < / P > < p > < p > < p > < p > how to use these data to calculate the "height" of Mount Everest? According to Guo Chunxi, first of all, the plane position and geodetic height of the datum network, regional frame network, local control network and peak joint survey network of Mt. Everest are obtained by using GNSS survey, triangulation and trigonometric leveling. Then, the normal heights of GNSS control points at all levels are obtained by using precise leveling and ranging elevation traverse. Then, using the high-resolution digital elevation model data, encrypted gravity survey data over the years, the new airborne gravity data, and the ultra-high-order gravity field model data at home and abroad, the high-precision gravity quasi geoid in Zhufeng area is obtained by using modern quasi geoid determination theory and removal recovery technology. Through the fusion of GNSS leveling, the high-precision quasi geoid results and the peak elevation anomaly in Mt. Qomolangma are obtained. Finally, the normal peak height is obtained by subtracting the peak height anomaly from the geodetic height of the peak. By calculating the average gravity and average normal gravity from the peak to the bottom of the peak, and then through the strict conversion of normal height and positive height, the positive snow surface height (altitude) of Mt. Qomolangma is obtained. The snow surface thickness of the peak is obtained by measuring the snow thickness radar, and the normal height of the snow surface at the peak is converted into the normal height of the rock surface. Guo Chunxi said that compared with 2005, the scientificity, reliability and innovation of the elevation survey of Mt. Everest have been significantly improved. Sun Heping, academician of the Chinese Academy of Sciences and researcher of the Institute of precision surveying science and technology innovation of the Chinese Academy of Sciences, wrote an analysis that the fixed-point gravity survey on the top of Mount Everest and the airborne gravity survey of 12500 square kilometers on the north slope will significantly improve the accuracy of the geoid in the Everest region, and provide the best starting datum for the elevation measurement of the highest elevation in history 。 Therefore, the accuracy of the Everest elevation survey will reach "the highest in history". < p > < p > < p > < p > < p > < p > < p > the data obtained from the scientific investigation of Mount Everest provide important data support for the accurate determination of the elevation of Mt. Everest, provide important data and technical support for the ecological environment protection, geological survey, crustal movement monitoring, topographic mapping, infrastructure construction, etc., and also for the maintenance and update of the national modern surveying and mapping benchmark system Lay a solid foundation and provide basic surveying and mapping guarantee for the service of natural resource management. (reporter Tao Xiuying)