# Application of the Segmented Correlation Technology in Seismic Communication with Morse Code
## 1 Introduction  
As early as 1899, scientists started to discuss how to implement a system of communication which could transmit signals through the earth [1]. During World War I, French physicists invented a geophone to detect underground activities in the battlefield, such as underground mining and tunnel excavation [2]. From the middle of the 1980s to the early 1990s, frequent seismic activities threatened the lives and property of miners, which drew the attention of the Canadian federal government, the Ontario provincial government and major mining companies. As a result, the technology of geophones gradually became a significant monitoring method for mine safety and ground control [3]. During the gulf war, the American military took full advantage of the electronic-jamming aircraft to destroy the air defense systems of Iraqi army, which paralyzed the radar systems of the Iraqi army so that the American military quickly won a victory on the battlefield [4]. During a mine disaster in Chile in August 2010, victims hammered a drill and attached a slip of paper to the drill to attract the attention of rescuers [5]. Over the last three decades, many methods have been proposed for communication in special circumstances where radio cannot operate, such as during mine disasters or wars, as mentioned above. To overcome this problem, [PERSON] conducted a seismic communication test, where hammering signals are encoded and filtered by a band-pass filter with a hammer and geophones [6, 7]. [PERSON] delineated the framework of the rake reception system by analyzing the multipath fading, which adopted time diversity and maximum ratio combination to reduce the bit error rate of propagation about seismic waves [8, 9]. [PERSON] discussed the transmission of seismic signals with direct sequence spread spectrum technology (DSSS), orthogonal frequency division multiplexing technology (OFDM) and code division multiple access technology (CDMA) [10]. He pointed out that a RAKE receiver could be used to solve the problem of multipath fading of seismic waves by MATLAB simulation [11].  
With the continuous development of urban underground space, many cities also face similar problems [12; 13; 14; 15]. Some countries would like to only develop shallow underground space to ensure the safety of people and quickly evacuate the population in case of accidents. For example, most underground spaces of cities in China are less than 30 m. However, the increasing cases of urban disaster are seriously endangering the health of the public and the safety of property. For example, on 2 December 2019, more than 1100 rescue workers and 192 emergency rescue vehicles were deployed in Guangzhou to search for underground victims due to the sudden collapse of the ground. On 7 January 2020, a worker was trapped for nine hours in a 30 m deep bomb shelter when an elevator suddenly failed, and his cell phone had no radio signal.  
Maintaining the connection between the underground and the ground when the communication of radio or cable is not available is an urgent task [16]. This is a feasible project, as [PERSON] mentioned, but there are many shock signals which might interfere with target signals. This study will discuss the influence of other vibration signals (especially the foot-step signal) in urban environments and explore how to make use of the SCTMC to extract target signals. For the sake of illustration, this paper will be divided into the following five parts: the principles and methods in seismic communication, the experimental process, the analysis of experimental data, discussion of experimental results and conclusion about the segmented correlation technology.