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Thermoacoustic Root Imaging

Stanford University

Thermoacoustic Root Imaging, Biomass Analysis, and Characterization

ARPA-E Award: 
Stanford, CA
Project Term: 
08/07/2017 to 08/06/2020
Project Status: 
Technical Categories: 
Critical Need: 

Plants capture atmospheric carbon dioxide (CO2) using photosynthesis, and transfer the carbon to the soil through their roots. Soil organic matter, which is primarily composed of carbon, is a key determinant of soil's overall quality. Even though crop productivity has increased significantly over the past century, soil quality and levels of topsoil have declined during this period. Low levels of soil organic matter affect a plant's productivity, leading to increased fertilizer and water use. Automated tools and methods to accelerate the process of measuring root and soil characteristics and the creation of advanced algorithms for analyzing data can accelerate the development of field crops with deeper and more extensive root systems. Crops with these root systems could increase the amount of carbon stored in soils, leading to improved soil structure, fertilizer use efficiency, water productivity, and crop yield, as well as reduced topsoil erosion. If deployed at scale, these improved crops could passively sequester significant quantities of CO2 from the atmosphere that otherwise cannot be economically captured.

Project Innovation + Advantages: 

Stanford University will develop a non-contact root imaging system that uses a hybrid of microwave excitation and ultrasound detection. Microwave excitation from the surface can penetrate the soil to the roots, and results in minor heating of the roots and soil at varying levels depending on their physical properties. This heating creates a thermoacoustic signal in the ultrasound domain that travels back out of the soil. The team's advanced ultrasound detector has the ability to detect these signals and maintain sufficient signal-to-noise ratio for imaging and root biomass analysis. The team will develop a suite of image processing algorithms to convert the data into an understanding of root properties including structure, biomass density, and depth. Plant physiologists from the Carnegie Institution for Science will partner with Stanford to characterize maize roots under various drought conditions as well as soil type and density variations. Since the entire system is non-contact, it eliminates the need to make good physical contact with the irregular soil surfaces. Over a three-year period, the team will first demonstrate the feasibility of non-contact thermoacoustics for root imaging under laboratory conditions, then develop and test a thermoacoustic system in the field. If successful, Stanford's system could examine root structures in a noninvasive manner that produces images far more advanced than current imaging methods.

Potential Impact: 

If successful, developments made under the ROOTS program will produce crops that will greatly increase carbon uptake in soil, helping to remove CO2 from the atmosphere, decrease nitrous oxide (N2O) emissions, and improve agricultural productivity.


America's soils are a strategic asset critical to national food and energy security. Improving the quality of soil in America's cropland will enable increased and more efficient production of feedstocks for food, feed, and fuel.


Increased organic matter in soil will help reduce fertilizer use, increase water productivity, reduce emissions of nitrous oxide, and passively sequester carbon dioxide from the atmosphere.


Healthy soil is foundational to the American economy and global trade. Increasing crop productivity will make American farmers more competitive and contribute to U.S. leadership in an emerging bio-economy.

ARPA-E Program Director: 
Dr. Joe Cornelius
Project Contact: 
Prof. Amin Arbabian
Release Date: