# Satellite-Based Wireless Sensor Development and Deployment Studies for Surface Wave Testing
## 1 Introduction  
Soil layers and rocks are complex, multi-phase, particulate, and discontinuous materials which cannot be described as a simple elastic model with fixed mechanical behavior [1, 2, 3, 4]. The soil layer's nonlinear and irreversible behavior has attracted the interest of researchers for decades [5, 6]. An underground structure, designed and built in the deep soil layer under the surface of earth, is a promising alternative to aboveground buildings for its resistance to severe weather, quiet living space, and energy efficiency due to the natural insulating properties of the surrounding earth [7, 8]. Likewise, underground transportation helps a major city become a better place by reducing traffic congestion as well as the overall level of pollution [9]. Although underground structures and transportation relieve the congestion resulting from the rapid increase in population, drawbacks remain. Underground construction activities have been challenged by the complicated mechanical behavior of the soil layers including their various thicknesses and main component [10, 11]. There is urgent need of accurate measurements on properties of the soil layer for geological exploration, subway, tunnel, and infrastructures constructions such as high buildings or long bridges [12]. To investigate the mechanical properties of soil, a seismic survey is represented, attempting to image or map the subsurface of the earth by sending sound energy down into the ground and recording the \"echoes\" that return from the rock layers below [1]. Several tests have been designed to measure or estimate seismic wave velocities in situ with the primary purpose of evaluating the mechanical parameters from the wave velocity, such as cross-hole test, down-hole test, multichannel analysis of surface wave [13], surface wave testing, etc. Surface wave as a non-destructive evaluation method is widely used in geophysics to infer the Rayleigh wave velocity of the subsoil for evaluation of the mechanical characteristics of soil layers. One common device for seismic survey is the geophone, which converts ground movement (velocity or accelerometer) into a time-history voltage signal to be recorded for the analysis of the structure of the measured earth. The geophone has been playing an important role in seismology measurement. While current cable-based seismic acquisition systems including geophone array and data acquisition system provide accurate records responding to the seismic testing, limitations remain [14]. The widespread application of cable-based acquisition system that has been stymied by the high cost of sensors installation and connection has warranted the emergence of the cost-saving wireless sensing system. Deployment and convenience are the main factors considered for seismic research and application. A wireless sensor is a response to limitations such as a large number of sensing channels and inconvenient deployment [15; 16]. For example, high-density land acquisition systems require as many as 50,000 live channels and a receiver density of 2000-3000 channels/km\({}^{2}\)[17]. For single-sensors, acquisition systems up to 1000-2000 receivers per line will be required with sensor spacing of 5-30 m. These parameters suggest adoption of an acquisition system that does not rely on cables. Furthermore, communication and detection reliability bring the field closer to studies on autonomous sensors that could collect, analyze, or share data \"smartly\" [18]. If the current trend of evolution continues with wireless sensors, it is likely that seismic monitoring systems will employ new transmission technologies to meet needs at every development stage. Key features of the main solutions for wireless communication are summarized in Table 1. Current wireless communications are grouped as short- and long-range communications. For short-range communication, the theoretical information transmitting range is from 10 to 160 m while the reliable range is less than the expected range considering the harsh environment and weather.