Performance Analysis of Convolution Enhancement of CEA Operator for Underground Geomagnetic Matching

  Obiectives  Underground geomagnetic positioning is a new method for emergency refuge and rescue. Its geomagnetic matching probability and accuracy will be affected by the richness and stability of the matching area. There is a problem of low probability of geomagnetic matching in some areas where the geomagnetic space changes gently.

  Methods  A convolution enhancement operator of the underground is constructed, named convolution enhancement algorithms(CEA), which is used to convolution enhancement processing of geomagnetic data in underground matching area and geomagnetic vector of the target moving track, so as to remove the noise of measured geomagnetic data and enhance the richness of geomagnetic information. CEA operator is a kind of convolution sharpening of geomagnetic features with column quantization, is the modification of Laplace, High Pass and Sobel operators of image convolution, which is suitable for underground strip area. The simulation test of mean-square-error algorithm(MSD) geomagnetic matching before and after the convolution of CEA operator is carried out, which data is the geomagnetic data of 4 tunnels in a gold mine.

  Results and Conclusions  The test results show that the statistical parameters of geomagnetic data fluctuate obviously after convolution by three CEA operators. The variation of geomagnetic data features before and after convolution by the High Pass operator is small, the variation of geomagnetic standard deviation and geomagnetic roughness is small, and the correlation coefficient sometimes even weakens. The information entropy of geomagnetic data before and after convolution by the Sobel oper‍ator is increased, which cannot keep the consistency of geomagnetic map trend, appears alienation. The Laplace operator has obvious enhance effect, which keeps the change of the original geomagnetic map, increases the difference degree of the data and reduces their correlation. Especially in the matching test of 600 ‍nT noise, the convolution processing of Laplace operator can reduce the impact of noise on geomagnetic positioning disturbance, improve the probability and accuracy of geomagnetic matching positioning, and show strong robustness, which is suitable for data preprocessing model of underground geomagnetic matching.