Development Of Multi-information Recording System For GREATEM Receiving Coil

The time-domain ground electrical source airborne transient electromagnetic method(GREATEM)is a rapid and efficient method of detecting the underground electrical structure by using the transmitting system placed on the ground and the receiving system installed on an airborne platform.Since the receiving coil of the GREATEM system is operated in the air during the measurement process,it is easily affected by the speed of the aircraft,the bumping of the aircraft,the turbulence,etc.The attitude changes of the aircraft bring an attitude error to the measured secondary field electromagnetic data and further affects the exploration effect.Therefore,besides collecting conventional electromagnetic signals,we need more information such as the coil attitude angles(pitch,roll,yaw)and the GPS information.During the GREATEM detecting process,each time corresponds to a specific measurement point,it is required to realize the fast and accurate calculation of the attitude angle corresponding to time.And the above multiparameter information is synchronized by the GPS Pulse per Second(PPS).It provides synchronous and precise attitude data for the attitude correction of electromagnetic signals,so that the following interpretation of the data is more accurate.At present,most researches about the coil attitude are limited to the theoretical analysis,numerical calculation and modeling simulation of the influence of attitude change on the electromagnetic response.Currently there is no receiving system with the function of attitude acquisition and recording for the GREATEM detection.In order to solve the above problems,in this paper,a multi-information recording system for the GREATEM detection is designed and implemented.The main research contents are as follows: 1)We describe the working principle of the GREATEM and calculate the electromagnetic response of the long conductor source.Then we simulate the electromagnetic response when the attitude of the coils changes by Matlab.After that,the general design of the multi-information recording system for the attitude of electromagnetic receiving coil in the GREATEM is proposed;2)We compare the direction cosine method,Euler angle method and quaternion method;combining with the working characteristics of gyroscope,accelerometer and magnetometer,the measurement scheme for attitude determination is developed.In view of the inevitable errors in sensor measurement in the coil attitude acquisition system,we apply data fusion by the Kalman filtering algorithm.A coil attitude error compensation technique based on Kalman filter is proposed,and its feasibility is verified by comparison;3)According to the design indicators of the multi-information recording system,we realize the hardware circuit design of the multi-information receiving system from four aspects.Including the design for the coil attitude acquisition circuit based on multi-sensor combination,the design for the electromagnetic signal acquisition conditioning circuit and the device selection,the technology of data collection and storage based on multi-process priority,and the technology of multiple parameters synchronization based on the GPS;4)The design of multi-data preprocessing software based on the software platform Matlab GUI is completed.The calibration,stability and linearity of the attitude acquisition subsystem are tested.The conventional performance indexes of the electromagnetic signal acquisition subsystem are also tested and the practical application experiments are completed in the field.All the above working proves the practicality and reliability of the receiving system.