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从几米到50公里距离的质子磁力仪差值测量的线性回归表明,时均值的标准偏差随测点间距的变化为δ=a+bd,其中a=0.07±0.02nT(1nT=1伽傌,译注),b=0.01±0.003nT/km,d为测点间距,单位为公里。当点距为几米且地震平静区与活动区测点噪声低时,时均值的标准偏差,对于0.25nT灵敏度的仪器为0.09—0.15nT。对于0.125nT灵敏度的仪器为0.07—0.08nT。这两种仪器的最小计数噪声分别小于0.07nT与0.03nT,而不确定的仪器噪声为0.04nT。在-6℃—21℃范围内,仪器的温度灵敏度不超过0.001nT/℃。对于在圣安德烈斯断层上10—15公里的点距,时均值δ的估计值在0.15～0.3nT之内,其数值依赖于局部磁性特征。频谱密度估计表明,差值场噪声功率随频率上升而下降,约为3分贝/倍频程。主要频谱峰值出现于日谐波和潮汐M_2频率之上。地磁差值场噪声限制了在低于2周/小时频率的测量能力,即仪器精度开始限制测定能力。如果预测滤波技术可以降低噪声谱的话,则可应用高灵敏的仪器。
The linear regression of the difference measurement of the proton magnetometer from a few meters to 50 kilometers shows that the standard deviation of the mean time varies with the spacing of the measuring points as δ = a + bd, where a = 0.07 ± 0.02nT (1nT = 1gamma, Annotation), b = 0.01 ± 0.003nT / km, d is the distance between measuring points in kilometers. When the dot pitch is several meters and the noise at the measuring point of the quiescent zone and the active zone is low, the standard deviation of the mean time is 0.09-0.15nT for the 0.25nT sensitivity instrument. For 0.125nT sensitivity of the instrument is 0.07-0.08nT. The minimum count noise of these two instruments is less than 0.07nT and 0.03nT, respectively, while the uncertain instrument noise is 0.04nT. In the -6 ℃ -21 ℃ range, the temperature sensitivity of the instrument does not exceed 0.001nT / ℃. For point spacing of 10-15 km on the San Andreas fault, the mean δ is estimated to be within 0.15-0.3 nT, and its value depends on the local magnetic characteristics. Spectral density estimation shows that the noise power of the difference field decreases with the increase of frequency, which is about 3 dB / octave. The main spectral peaks appear above the daily harmonics and the tidal M_2 frequency. Geomagnetic field noise limits the ability to measure at frequencies below 2 weeks / hour, ie instrument accuracy begins to limit the ability to measure. If the prediction filter technology can reduce the noise spectrum, you can use highly sensitive instruments.