加权谱比法Q值估计

谱比法是现今最常用的Q值估计方法之一。当地震数据中含噪声时，常规谱比法稳定性差且Q值估计结果依赖所选取频段。缘于常规谱比法在利用最小二乘拟合直线时采用的是等权重法，导致其拟合结果受低频和高频区异常值影响较大。为了提高谱比法的稳定性，降低其对频段选取的依赖性，提出了加权谱比法Q值估计方法。在进行最小二乘拟合时，引入高斯函数作为权重因子，降低低信噪比信号的权重系数；且高斯函数的峰值频率和方差分别选用震源子波的质心频率和方差。模型测试结果表明，相对于常规谱比法，加权谱比法的稳定性增强，对频段选取的依赖性降低；实际VSP资料应用进一步证实加权谱比法可稳定、有效地估计Q值。

Qfactor estimation by weighted spectral ratio me-thod

The spectral ratio method is currently one of the most commonly used Q factor estimation me-thods. When seismic data contains noise interfe-rence,the spectral ratio method has poor stability and the estimation result depends on the selected frequency band. This is because equal weights are used in the Q factor estimation by the spectral ratio method when the least-squares method is employed to fit a straight line. As a result, the fitting results are greatly affected by the abnormal values in the low and high frequency regions. To improve the stability of the spectral ratio method and reduce its dependence on the selection of frequency bands, this paper proposes the weighted spectral ratio method for Q factor estimation. During least-squares fitting, a Gaussian function is introduced as a weighting factor to reduce the weighting coefficients of signals with low signal-to-noise ratios. The peak frequency and variance of the Gaussian function are the centroid frequency and variance of the source wavelet,respectively. The model test indicates that the weighted spectral ratio method is more stable than the conventional spectral ratio method,and its dependence on frequency band selection is reduced. The application of actual VSP data further proves that the weighted spectral ratio method can estimate the Q factor stably and effectively.