微型盒子波(Micro Box Wave Test,MBW)可以被用于检波器灵敏度、允差、最低有效频率以及自然频率、阻尼(限于动圈式检波器)的野外现场标定.根据奈奎斯特频率内不同频段的地震检波系统的主导因素,对地震勘探有意义的频率范围可以划分为六个不同的频带.频带20～40 Hz是确定10 Hz动圈式检波器的灵敏度和允差的适用频段.同时,微型盒子波初至时间的最大值相对平均值的偏差可以计算某种类型检波器的总体允差(Tolerance in General).总体允差过大时,由检波器自身因素导致的不一致性会淹没微弱的深层反射信号.另外,在具体工区、具体采集参数的情况下,基于"微型盒子波"方法也可以计算不同类型检波器的"最低有效频率",该指标可以说明检波器的低频拾取能力.最后,如果把无低频衰减的检波器作为标准检波器,可以标定动圈式检波器的自然频率与阻尼两个参数.数据表明,根据动圈式检波器自然频率与阻尼对其拾取的原始数据做检波器反褶积后,其低频分量与无低频衰减的MEMS检波器具有高度一致性.目前的地震采集项目广泛应用动圈式10 Hz检波器施工,该型检波器损失的低频部分经检波器反褶积恢复后,在处理、解释阶段的应用值得进一步深入研究.
Approach to calibrate the geophone specifications via micro box wave test
Micro Box Wave Test(MBW)can be used for field calibration of geophone sensitivity,tolerance,lowest effective frequency,natural frequency and damping(limited to moving coil geophones).According to the dominant factors of seismic detection system in different frequency bands within Nyquist frequency,the whole frequency range of interest for seismic exploration can be divided into six different frequency bands.For the most widely used 10 Hz moving-coil detector in current construction,the frequency band of about 20～40 Hz is suitable for determining the sensitivity and tolerance of the detector.The deviation between the maximum value of the first arrival wave and the mean value of the micro-box wave indicates the Tolerance in General of a certain type of detector,which is of great significance for recognizing weak signals from deep targets in noisy environment.When the overall tolerance is too large,the inconsistencies caused by geophone factors will overwhelm the weak deep reflected signal.In addition,under specific work areas and collection parameters,the"micro box wave"method can also calculate the"minimum effective frequency"of different types of detectors,which can demonstrate the low-frequency pickup ability of detectors.Finally,if the geophone without low-frequency attenuation is taken as the standard geophone,the natural frequency and damping parameters of the moving coil geophone can be calibrated.The data shows that according to the natural frequency and damping of the moving coil geophone,the low-frequency component of the original data picked up by it is highly consistent with the MEMS geophone without low-frequency attenuation after the geophone deconvolution.The current seismic acquisition projects widely use dynamic coil 10 Hz detectors for construction,and the application of low-frequency signals recovered through this method in the processing and interpretation stages is worthy of further in-depth research.
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