Using Distributed Temperature Sensing (DTS) to Assess Soil Moisture In Agricultural Settings

Distributed temperature sensing (DTS) systems provide the opportunity to monitor at a high level of precision and accuracy and at high spatial and temporal frequencies, water, air and media temperatures in a variety of systems. However, to date, there have been relatively few environmental or scientific applications of DTS. We attempt to evaluate soil moisture in an agricultural environment in the Walker Basin, northwestern Nevada, using Raman spectra DTS through fiber optic cables. Cables were installed approximately 10 cm below the soil surface in two agricultural fields with distinct soil types, and temperatures were monitored periodically under different conditions, including dry soil before planting, irrigated soil with little to no plant growth, and irrigated soil with significant plant growth. Different irrigation regimes and plant types were distributed throughout each field, and soil samples from 10 cm and 20 cm were collected bi-weekly throughout the study period. Preliminary data indicate that the thermal signals produced in dry versus moist soils are significantly different, and that these data correlate well with both the onset of irrigation and soil moisture measured in soil samples. Because fiber optic cables could be buried at any depth for application of DTS, this method provides a potential advantage over traditional plane- or satellite-based imaging techniques for assessing soil moisture that are limited to assessing only the top few centimeters of soil. In addition, periodic monitoring of such cables can provide information on the uniformity (or lack thereof) of soil moisture distributions at depth during and after irrigation and plant growth.