Soil moisture assessment by means of MEMS tri-axial accelerometers

The main purpose of the present work is to design and build a prototype system based on seismic sensors for the measurement of the degree of saturation in unconsolidated granular mediums. In previous papers (F. Adamo et al., 2004), (F. Adamo et al., 2006) the authors have described the theoretical analysis necessary to estimate the degree of soil saturation which is obtained by measuring the propagation velocities of both compressional and shear seismic waves. The knowledge of a general mathematical model based on theories of propagation of elastic waves has enabled the development of a first prototype of the system. The more in depth analysis of the first experimental results (F. Adamo et al., 2007) has highlighted the validity of the theoretical model but has also revealed some limits of the previously designed hardware. Considering these limits, the authors have developed an improved system based on very cheap tri-axial accelerometers: this prototype assesses the moisture in the soil with an acceptable measurement uncertainty. In this paper major emphasis is given to the description of the custom-built hardware and to the measurement method. This paper is arranged in three different sections: in the first section we present the mathematical model resume, in the second one we describe the last prototype developed to improve the performances of the measurement system in terms of measurement uncertainty, reliability and noise immunity: in the third section we characterize the measurement technique and the experimental setup.