Data Recording And Field Processing Of Helicopter-borne TEM

Helicopter-borne Time-domain Electromagnetic Method (HTEM) has rapid large-scale electromagnetic geophysical advantages and it is used for metal ore exploration, geological mapping, hydro geological surveys and environmental monitoring. After 2000, five aspects abroad has rapidly developed, such as airborne electromagnetic forward and inversion methods, the special data processing methods, helicopter electromagnetic instruments, instrument calibration methods and application. The 1D, 2D and 3D forward, invention model simulation, and conductivity depth imaging problems have been studied. Special data processing studies include the impact of the flight program of exploration, the influence of the bird posture change, data leveling and the good conductor detection. The most advanced HTEM systems are developed to wider frequency band, high-power transmitter and multi-component receiver. From the three calibration methods about the known loop detection method, the contrast correction method of the actual conductor and the performance of the system itself, this thesis is chose artificially controlled loop detection method. HTEM's applications have become more and more widespread throughout continents, such as inland surface and groundwater exploration, shallow sea and salt water intrusion investigation, sea and ice depth detection, mineral exploration, natural disasters exploration about volcanoes, the falling rock and tunnels, underground exploration, pollutants investigation, coal, oil and gas exploration, unexploded ordnance detection, and vegetation cover survey.Because there is no airborne electromagnetic system equipment inboard, Chinese researchers just do studies about the theory and model simulation. Considering the mountainous terrain in China and HTEM detecting deep advantage, this subject is supported by the national eleventh five-year 863 plan. The target is to develop a practical HTEM system.Innovations of this thesis include that a bird calibration device of HTEM with concentric bucking loop, combination of two methods about bucking loop and lower-noise dual-channel sampling program is improved the dynamic range of the HTEM signal, multi-information fusion based on Time-flow FID method is achieved, and single-file storage method can avoid the system crashing because of the competition of a hard disk written, which is described four chapters.(1) The real-time full-wave method of huge data recording provides more information for helicopter-borne time-domain electromagnetic instrument with respect to deep exploration and spatial discrimination. Considering the lack of compatibility between large magnetic moment and full-wave recording approach in the coaxial coplanar coils'device, this thesis uses bucking coil to weaken the primary magnetic field, and applies the key technology of state-machines, the design of multi-tasking mode, information stored method and data fusion of time-based stream on the base of continuous sampling characteristics of high-precision and long time. Combination of two methods about bucking loop and lower-noise dual-channel sampling program is improved the dynamic range of the HTEM signal. Finally, the full-wave recording system with the core of PXI is developed. A series of experiments show that the system is stable and reliable, and provides application platform for method research and reference for the design of electromagnetic instruments on unmanned aerial vehicles and semi-airborne.(2) The multiple instrument calibrations of flying helicopter-borne time-domain electromagnetic method can eliminate the environmental time-varying effect on the system during the process of flying. Using the bird calibration device to solve the problem that the wire-loop method can't achieve, this thesis considers the bird model of HTEM with the concentric bucking loop, bringing forward the bird device space models and the coil circuit models, and analyzing the transmitter magnetic field distribution, the bucking loop's effect and the relationship between it and the receiving coil, the space information of the calibration device and its signal detected method. Conclusions are as follows: (a) The bucking loop that loses 0.89% of the transmitting area can increase 44.5dB of the signal dynamic range. (b) The calibration device is levelly placed between the bucking loop and the transmitting coils. If it has more turns, greater radius and is closer to the bucking loop, its signal response becomes stronger. (c) If the inductance of calibration coil becomes greater with less resistance, its exponential decay becomes more slowly. The signal detection time-point is directly decided by damping character of receiver coil, which has matching resistance. This thesis is based on experiments about the calibration curve characters and the device coil displacement. The relative error about the time constant of the device characteristics is less than 1.3%, which proves the validity of the coil circuit models and device space models. The proposed models and approaches are also the same as the bird calibration device research about HTEM with the eccentric bucking loop and the known wire-loop static testing on the high resistance ground.(3) The key technologies of on-site rapid processing of large amounts of data are the measured information management, the separation of information, the main sampling waveform processing, the information fusion of time-based stream, and large memory multi-core parallel processing method. The functions of the test profiles'software are time adjustment, survey line information division, survey lines of removal high-altitude background information and generating function of the standard profile file.(4) In order to verify the overall performance of the instrument and the initial flight data processing, this thesis designs the experiments that the crane swings the bird to detect the ground loop anomaly. Based on the ground loop detection theory, the mobile loop anomaly is simulated by different parameters. The measured profile curve information demonstrates the feasibility of the instrument movement measuring. The loop processing of the onboard calibration profile can simulate the real flight data processing.In this thesis, the system has done many ground experiments Geological Palace, Big Goose Island, Karen Lake and Shaoguo town in Changchun, and it is successfully used to find water resource combined with NMR in Yunnan and Guizhou province in 2010. However, the bird framework is broken in the helicopter experiment. Further research should be emphasized on the weight reducing of the system and the the interference removing of the current modulated signal.