The Key Technology Of Near Space Gravity Survey

Earthquake is one of the most serious disasters in the nature,and it is the form of the complex physical process inside the earth.When earthquake prepared and finally happened,the substance of the earth interior will redistribute and this processing also lead to changes of gravity fields both in time and space.Therefore,the monitoring of the gravity changes is one of the main methods of modern earthquake monitoring.In recent years,gravity monitoring is mainly composed by mobile gravity monitoring,station gravity monitoring and satellite gravity monitoring are also used to monitor gravity changes background.But such kinds of ways have some disadvantages.Mobile gravity monitoring is easily influenced by geographical condition and is low efficiency;station gravity monitoring is limited by the technology of the instruments and can only obtain data of single point.The satellite gravity monitoring is used to analyze the background of the gravity changes,and can hardly be used to analyze the risk of the earthquake happening.Furthermore,because of the limited accuracy,today's airborne gravity only can be used to study the crust's structure but has some limitation in monitoring the gravity changes caused by earthquake.Near space is a concept that the space that above the ground 20~100 km.At this altitude,the observation can be used to study the lithosphere's structure,and this result is far concerned to be significant to study the earthquake preparation.With the development of our country's near space aircraft,especially the series ‘rainbow',the platform for near space gravity monitoring is available.This series of aircraft is powered by solar energy which makes long period observation possible.And this kind of long period observation benefits the earthquake-background analysis.In the same time,compared with the satellite,the near space aircraft costs less and is more efficient.As a result of all those advantages mentioned above,the observation system based on near space aircraft has a potential to complete the all-around gravity observation system and provide platform for the military survey and resource survey.Near space gravity survey is main part of the gravity monitoring in the future.This paper is based on reality and focuses on the lithosphere's structure.Through calculating the gravity changes in the near space when an earthquake prepared,this paper put forward some demands for the near space gravity survey system.Taking the gravity changes before the Jiuzhaigou earthquake as an example(about 2000 points in Jiuzhaigou district),pre-treating the survey data.Calculating the upward continuation by Kriging method,the results shows that to discover the gravity changes before a Ms=7 earthquake the near space gravity survey need to distinguish 0.1 m?Gal gravity changes.Some researches show that,traditional airborne gravity survey cannot be applied to the earthquake monitoring because of the limitation of the DGPS technology.So this paper discus the gravity gradiometer.And calculating the aircraft gradiometer correction at first.Now days,the near space gravity survey is a brand new technology and has many problems to solve.This paper proposes the request about the sensor and simulates the gradiometer of the aircraft itself.In the next,we also need to discuss the downward continuation method,the filtering algorithm and the atmosphere model correction.