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.