Research On Techniques And Methods Of Gravity Inverting In Searching Underground Cavity

Underground cavities have a significant practical value in civilian and military,so searching and detecting for them are of great significance.Compared with other detecting technologies,gravity surveying isn't only more economic and efficient,especially in a wide range of area,but also has its natural advantages in concealment of detecting and anti-interference from the environment.With the constant improvement in the precision of gravity instruments and the continuous development of airborne gravity survey and unmanned aerial vehicle?UAV?gravity survey,gravity surveying will have a greater effect in the field of detection.This article mainly studied the issue about techniques and methods of gravity inverting in searching underground cavities.The main work and innovative ideas in this paper are presented as follow:?1?The boundary identification operators consisted of higher derivatives of gravity gradient tensor have been proposed,also the Sigmoid conversion.And the recognition effect of each operator and the enhancement effect of the Sigmoid conversion were analyzed by simulation experiments.The results showed that the ITA₂ and the ITA₃ can effectively balance the anomaly information of underground cavities with different depths,which also have a better effect on extracting the boundary of underground cavities than the regular operators.And the ITA₃ had the best accuracy in boundary recognition,also amplifing the influence of noise at the same time.And the ITA₂ had a best effect in boundary recognition for shallow underground cavities,with the results being a little bigger than the real boundary.When the values of abnormal data in the grid are lower,the effect of recognition can obviously be improved by Sigmoid conversion.?2?The basic principle of Euler deconvolution inversion algorithm and its calculation methods were introduced,and the inversion effects of them were analyzed by simulation experiments.The results showed that the Euler deconvolution inversion algorithm had a better performance in inverting the parameters such as position and depth of underground cavities,but there were also problems such as multiple solutions and solution divergence.After the improvement,although there was a large error in the interpretation of depth caused by the error of the locating of the extreme value of analytical signal,the problem of multiple solutions was solved,and the inversion results were more accurate.?3?The program of searching for underground cavities by gravity surveying was designed.The relationship between the observation accuracy and the abnormal data reliability of underground cavities was analyzed,and two discriminated method for reliability of the abnormal of the underground cavities in two different cases were proposed.The influence of the laying of the lines and the height of the flight on the abnormal values of underground cavities were analyzed by forward simulation experiments.For the underground cavities which model and size were known?established by intelligence information or search task?,the planning method for lines spacing and flight height was proposed before probing.?4?The method in determining of target area by analytic signal was proposed,and the efficiency in searching has been greatly improved.The effects of determining of target area by analytic signal and by gravity abnormal were analyzed through simulation experiments.The results showed that the target areas determined by analytic signal were smaller,and not suffering from the interactions between the underground cavities.In the monomer simulation experiment of this paper,the target area determined by analytic signal and gravity abnormal were 4km² and64km² respectively.In the combination simulation experiment,with the increaseing of the interactions between the underground cavities,the amount of the target area determined by gravity abnormal were from 2 to 1,and the area were 74km²?76.5km² and 63.75km² respectively.And the amount of the target area determined by analytic signal were always 2 with the area being always 4km² and 1km² respectively.?5?The search strategies for the underground cavities in two different cases which model and size were known or not were proposed,and the effects of searching were analyzed by simulation experiments.The results showed that the search strategies proposed in this paper can search the underground cavities efficiently and accurately.In the simulation experiments of this paper,the location of the underground cavity searched by the search strategy for the underground cavities which model and size were known was basically consistent with the location of the model,and the error between solved depth 0.68?the unit is 100m,the same below?and the depth of model was only 0.02,and the solved boundary in approximately square shape with the length2.1 was close to the real boundary of model in square shape with the length 2.0.And the location of the underground cavity searched by the search strategy for the underground cavities which model and size were unknown was basically same with the location of the model,so was the solved boundary in approximately rectangle shape with the length 5.90 and the width 2.98 with the real boundary of the model in rectangle shape with the length 6.0 and the width 3.0,and the solved depth 1.54 was very close to the real depth 1.50 of the model.