The Study Of SNMR Real-time Reference Noise Cancellation Method Based On LabVIEW

The Magnetic Resonance Sounding(MRS) is the only one non-invasion direct geophysical groundwater detection method. The MRS underground water detection method have been studied for several decades, the detection capabilities of instruments develop from single channel to multi-channel;the denoising methods develop from digital overlay, power frequency notch filter to adaptive notch filter, figure 8 coil,wavelet analysis,nonlinear energy operator,adaptive filter and modern data processing techniques.. Through the continuous development of the instrument and data processing method, MRS technology has been widely used in the field of groundwater resource exploration.Although important progress has been made,the MRS signal is weak and normally n V, the traditional MRS data processing method is generally uploading the collected data into the host computer to eliminate noise and subsequent inversion interpretation at the end of the field experiment. However, in the high noise environment, the direct observation of MRS signals in the field is difficult, can not directly determine the performance of the instrument and the effectiveness of the collected data. Therefore, transplanting the MRS data processing method into the hardware system, and carrying out the data acquisition directly after the end of the data acquisition is very necessary. In this thesis, a real-time adaptive reference noise cancellation method is proposed based on the multi channel MRS detection instrument, in order to meet the goal of real time and fast processing, the Least Mean Square(LMS) algorithm with variable step size is studied; real-time reference noise cancellation system is designed and its hardware and software platform are built; design the variable step size LMS algorithm is based on the Lab VIEW platform, and the effectiveness of the algorithm is verified by theoretical simulation; download the algorithm to the FPGA system, realizing the MRS signal real-time reference noise cancellation.Using the simulated MRS signal test the system in school environment,add measured noise to the simulated MRS signal,when SNR is-26.82 d B, after real-time de-noising, the SNR can reached-6.05 d B; Field experiment was conducted in North suburb of Changchun, two 25 m X 25 m reference coils were set away 25 meters and 50 meters from the main detecting coil separately, after using the real time de-noising algorithm, the noise level of three experiments all decreased above 10 d B, and can directly observe the de-noising effect real-time in the computer system, which verifies the practical effectiveness of real-time noise reference cancellation method based on the Lab VIEW.In this thesis, the real-time reference noise cancellation method based on Lab VIEW improve the ability of the MRS instrument obtaining effective MRS signal in the strong noise environment, it can be used to observe the effect of noise elimination in the field, and determine the performance of MRS detection instrument, so as to improve the efficiency of field work, which have important significance for expanding the application range of MRS method and promoting the progress of magnetic resonance technology.