伪随机编码源激发下的时域电磁信号合成

将伪随机编码技术引入到人工源电磁法后，可以通过加大发射功率以及应用后续的相关处理技术来达到压制噪声、加大探测深度及提高分辨率的目的，因此引起了越来越多学者的关注及研究，但大多数研究集中在资料处理的相关技术上，对模拟电磁信号关注较少.然而，资料处理工作大多是从电磁信号出发的，模拟伪随机编码源激发下的电磁信号不但可以为资料处理环节提供理论数据，而且可以为检测资料处理的效果提供中间结果，因此，模拟电磁信号工作必不可少.本文根据获得接收信号的物理过程来实现伪随机编码源激发下的电磁信号合成.首先用解析公式获得特定地电结构的大地频率域响应，然后通过余弦变换得到时间域阶跃响应，接下来用阶跃响应的时间导数得到大地脉冲响应，通过将大地脉冲响应与伪随机编码源的褶积得到理想接收信号，最后，用低通滤波器来模拟发射设备和接收设备的频带限制，将之和噪声一起加到理想接收信号上，最终模拟出仿真的合成信号.通过和野外实际接收信号对比发现本文合成信号仿真度较高，可以服务于后续的数据处理环节.

Signal synthesis of time-domain electromagnetic response excited by a pseudo random binary sequence source

After the pseudo-random binary sequence source is introduced into the artificial electromagnetic method, the exploration depth and the resolution are improved, because in this approach correlation technique can be used in the data processing to suppress noise. Most researchers didn't focus on the synthetic signal rather than data processing. However, some data processing techniques have to use the electromagnetic signal, therefore it is indispensable to rely on synthesis of electromagnetic signal. In this paper, the electromagnetic signal is synthesized according to the propagating routine of the electromagnetic field. Firstly, electromagnetic response of a simulated geo-electric model in the frequency domain is calculated according to analytic formula. Secondly, the step electromagnetic response in the time domain is obtained by applying cosine transform to the response in the frequency domain, and then impulse response of the earth is obtained from time derivative of the step response. Through convoluting the impulse response of the earth and with PRBS source, the ideal electromagnetic signal can be composed. Finally, a low-pass filter is used to simulate the synthetic system response of the transmitter and receiver because all of the instruments are band-limited. Then the simulated signal is obtained by convoluting a low pass filter to the ideal signal added with noise. Comparing with actual field received signal proves that the composed signal is correct, and the signal of high simulation can be used to serve the data processing technique.