Research On Measuring Instruments And Correction Of Aeromagnetic Total Field Gradient

Aeromagnetic is a detecting method with a magnetic instrument mounted on an aircraft.It has the advantages of high work efficiency,wide coverage area,etc.It has always been attached importance to by magnetic workers.Aeromagnetic mainly includes magnetic total field measurement and magnetic total field gradient measurement.Compared with magnetic total field measurement,magnetic field total gradient measurement has obvious advantages in spatial resolution,which has stronger ability to distinguish complex magnetic anomalies and also can quickly determine the shallow anomaly field inference.In addition,it has a certain significance for the study of magnetic gradient tensor.Therefore,this paper mainly studies the total field gradient measuring instrument and the correction of total field vertical gradient.(1)The instrument research includes the verification of various performance indicators of the Overhauser magnetometer,mainly focusing on experiments with sampling rate,poor steering,and GPS impact.The conclusions are as follows: when the sampling rate is set to 1Hz,the noise is small and the data quality is high;there is no deadlock problem,but there is a direction difference;when the distance between GPS and sensor is longer than 28 cm,there is no effect.Aiming at the shortcomings of the existing fluxgate gradiometer data collector,a collection system was developed.The whole system is mainly divided into mechanical part,electrical part and software control part.The mechanical part by using the Siemens UG software to design case and module geometry,and uses non-magnetic aluminum alloy materials to complete the chassis processing;The electrical parts adopting the idea of modular,it can be mainly divided into four parts: the main control module,data acquisition module,host computer module,power supply module.The software control part is divided into: acquisition card control,data acquisition,data transmission,human-computer interaction and data storage in five parts.The entire acquisition system is light and magnetic interference is very small,so it is especially suitable for aerospace applications.(2)According to the changes of the attitude of the gradiometer during the aeromagnetic exploration,a vertical gradient correction method is proposed.The basic idea is that the magnetic dipole is used as a magnetic anomaly to simulate the change of the height and tilt angle of the gradiometer and obtain the simulated gradient data,when the aircraft is flying in the survey area.The simulated gradient data was corrected according to the proposed method,and the corrected vertical gradient value was basically consistent with the ideal situation.The improvement ratio before and after calibration reached 30.5,which proves the feasibility of the algorithm.(3)In order to verify the correction method and the performance of the fluxgate gradient meter acquisition system,several field experiments have been carried out.Firstly,the measurement attitude of the Overhauser total field gradiometer was measured on the ground using a non-magnetic trolley,and corrected by the previous mentioned correction algorithm.The improvement ratio of the gradient data before and after correction was 1.12.Secondly,the detection experiments of Overhauser gradiometer equipped on helicopter were carried out in Siziwangqi in Inner Mongolia,the feasibility of this correction method can be proved by comparing the total field anomaly and corrected field gradient anomaly.In order to verify the practicality of the fluxgate gradiometer system,a six-rotor unmanned aerial vehicle detection experiment was carried out.The scale factor error,non orthogonal error and zero bias error of fluxgate were analyzed and modeled,and corrected by ellipsoid fitting method.The calibrated line vertical gradient data can detect the distribution of magnetic anomalies and prove the effectiveness of the developed acquisition system.The research work completed in this paper can provide a certain technical support for the gradient measurement of aeromagnetic total field,and it also provides experience for the airborne magnetic gradient tensor detection.