Non-invasive acoustic-seismic sensing of soils

Lead Research Organisation: University of Manchester
Department Name: Electrical and Electronic Engineering

Abstract

A method for non-invasive sensing of soil structure and the mechanical strength of soil would permit better decisions about appropriate soil management practices. The lack of suitable methods to measure soil physical characteristics directly that are relevant to crop growth and soil environmental function (e.g. absorption of high intensity rainfall) are barriers to the development of approaches for sustainable soil management. Soils may be regarded as partially-saturated porous media. The acoustical properties of air-filled porous media have been studied widely in various contexts. Models for these properties incorporate parameters related to the frame elasticity and the pore structure. The most widely-used model, Biot theory predicts that such media support two kinds of coupled compressional waves, sometimes called Type I and II waves, and a shear wave. The Type I and shear waves travel mainly through the solid matrix and involve interactions between particles. They are equivalent to the P- and S- waves induced by direct mechanical excitation, for example during a seismic refraction survey. The Type II wave travels mainly through the fluid-filled pores being attenuated by viscous friction and thermal exchanges. It is dominant during acoustic excitation i.e. from sound sources above an unsaturated soil surface since the primary path for sound into the soil is through the pores connected to the surface. Recently it has been demonstrated that the P-wave velocity in soil is highly correlated with the internal stress in a soil. This suggests that P-wave velocities determined remotely from non-invasive acoustic-seismic probing can be used to measure mechanical stress in soil and hence its resistance to root elongation. Furthermore measurements in the laboratory and in instrumented pits outdoors have shown that the velocity and attenuation of sound in soil is related to soil density, water content, matric potential and porosity. The applicants (Attenborough and Taherzadeh) have developed a model (PFFLAGS) to predict the interaction of sound with layered soils, from sources above or within the soil that takes into account both soil mechanical and structural properties. By applyng this model to a combination of acoustic measurements using probe microphones and seismic measurements using geophones it has been found to be possible to obtain values of several soil parameters in reasonable agreement with independently measured values. Of course techniques using buried microphones and geophones are invasive. There remains a need to develop non-contact non-invasive acoustical techniques and to extend them to encompass the determination of moisture content. In this project we propose to investigate the conjunctive use of microphone measurements of reflection from the soil surface of sound from a point source (loudspeaker) and scanning Laser-Doppler Vibrometer (LDV) measurements of the seismic surface response to such insonification.We propose to develop the theory and practical knowledge needed to deduce permeability (a physical property of soils that depends strongly on the number and connectivity of macropores), moisture content and the internal stress in soil and to map these quantities as a function of depth. The proposed technique will serve as a prototype for subsequent engineering development of systems for automated data acquisition and processing in the field.

Publications

10 25 50
publication icon
Newill P (2014) Electrical impedance imaging of water distribution in the root zone in Measurement Science and Technology

 
Description EIT system developed in partnership with OU and Rothamsted Research to complement acoustic soil architecture monitoring system (i.e. EIT system offered information on movement of moisture and electrolytes in and around hard-pans).
Exploitation Route The EIT techniques developed and demonstrated within the trial pit at the OU has shown that the non-invasive, real-time, technique is scalable and potentially applicable to a broad range of biotic and abiotic crop stress monitoring duties. This has led on to downstream research activities related to IoT sensors for irrigation management through to crop phenotype screening for preferential input traits (see narrative section). The core technology may thus be taken forward as a tool/technique within land and farm management or through complementary duties in crop selection and breeding. This has recently been demonstrated for clubroot pathogen detection.
Sectors Agriculture, Food and Drink

 
Description Follow on work on subsoil phenotyping. Additional research strand has now been opened up on sub-soil non-invasive sensing of root-based pathogens, notably clubroot in brassicas. This has yielded positive results and is now subject to a paper submission to the 'Plant Methods' journal, in partnership with Sheffield University Plant Protection group.
First Year Of Impact 2017
Sector Agriculture, Food and Drink,Digital/Communication/Information Technologies (including Software),Electronics
Impact Types Economic

 
Description IKnowFood: Integrating Knowledge for Food Systems Resilience
Amount £590,212 (GBP)
Funding ID BB/N020626/1 
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 10/2016 
End 10/2020
 
Description Phenom-UK Launch Conference 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact The 3D multispectral system research forms part of the original BBSRC Phenom-UK project proposal, of which the PI (Prof Bruce Grieve) was a co-author. The multispectral research and technology, as well as the subsequent commercial variant of the technology, in the form of products from the Fotenix Ltd spin-out, have secured a slot to be presented at the launch event on 11th February 2020.
Year(s) Of Engagement Activity 2020
URL https://www.phenomuk.net/event/phenomuk-annual-meeting-at-national-physical-laboratory-teddington-fe...