**5. Conclusions and Discussion**

Considering that the outliers in the complex engineering environment have a serious effect on the location performance, the PCFWE method is proposed to improve the location accuracy in this paper. Firstly, the weight estimation is developed by transforming residuals to weights according to normal distribution. Updated weights are incorporated into the source location to provide a weighted least squares solution. Then, outliers are filtered by iterating between the weight estimation and source location. Linear equations, which are reconstructed with remaining measurements after filtering outliers, are ill-conditioned and need to be preconditioned to lower the condition number. Finally, the optimal source coordinates can be obtained by solving preconditioned linear equations. The proposed location method is verified by the experiment of pencil-lead breaks; the results show that the proposed PCFWE method achieves a stable and accurate location both with outliers and without outliers in measurements. However, how many outliers the proposed method can tolerate, and the sensitivity of the wave velocity, still need further investigation.
