Date of Graduation


Document Type


Degree Name

Bachelor of Science in Biological Engineering

Degree Level



Biological and Agricultural Engineering


Costello, Thomas

Committee Member/Reader

Costello, Thomas

Committee Member/Second Reader

Le, Kieu

Committee Member/Third Reader

Brye, Kristofor


A crucial measure in the advancement of water conservation and sustainable agricultural strategies is increasing efficiencies of irrigation systems. Because of the lack of availability of affordable, durable, and scalable soil moisture monitoring devices, this thesis proposes a low-cost, multi-depth soil temperature sensor array as a candidate for monitoring soil moisture content and guiding farmer’s irrigation scheduling. Propagation of diurnal temperature waves through soil is dependent on the thermal diffusivity of the soil, which can be determined by examining temperature waves at different soil depths. Thermal diffusivity is dependent on several factors, though, in undisturbed soil, water has the largest impact on changes in thermal diffusivity. Therefore, it is hypothesized that a multi-depth temperature sensor array can be used as an indirect method of measuring soil moisture content.

The main goal of this thesis was to test the ability of prototypes of the sensor array to collect consistent, repeatable multi-depth temperature; it was hypothesized that a coefficient of variation (CV) of 10% or less could be achieved in temperature readings at a given depth from multiple, adjacent probes. A prototype was designed using a list of design objectives, and a standard method of prototype construction was developed. Eight prototype probes, all fabricated with the same processes, were tested in two different locations in order to observe the repeatability between their measurements. The collected data demonstrated expected behavior, such as increased amplitude damping and phase lag with increasing depth.

The temperature data at a given depth for each plot had a maximum CV of 3.0%, indicating a successful level of repeatability of the sensor arrays. Sinusoidal nature of some residuals, although small (generally less than 0.3-0.4 °C), could represent error introduced by imprecise depth placements; therefore, further design effort to improve the construction process that ensures better precision could be helpful. These devices appear to have the potential to be developed into inexpensive soil moisture sensors.


Sustainable agriculture, Irrigation, Agriculture technology, Water conservation