In situ measuring soil ice content with a combined use of dielectric tube sensor and neutron moisture meter in a common access tube

For monitoring soil water dynamics in cold regions, the major concerns are not only liquid soil water content (LSWC) and total soil water content (TSWC), but soil ice content (SIC) as well. The field determination of SIC is more challenging than that of LSWC or TSWC and no practical method has been found. This study presents a method that combined a neutron moisture meter (NMM) with a dielectric tube sensor (DTS) lowered in a common access PVC-tube, in which NMM was for determining TSWC and DTS was for LSWC. Consequently, the absolute difference was of SIC. The proposed method was tested in an agricultural field over the winter of 2011–2012. Field calibration and a cross-check showed that DTS and NMM measurements in the common access PVC-tube were very similar (R2 = 0.9503, RMSE = 0.0197 cm3 cm−3) to the volumetric soil water contents (VSWCs) ranging from 0.05 to 0.40 cm3 cm−3. More importantly, the results of overall experimental period confirmed that both sensors had the same responses in the unfrozen layers but different responses in the frozen layers. Based on this, we transformed the measurements of both sensors into SIC. Furthermore, for characterizing the SIC dynamics during the overall experimental period, we presented the curve-based results and the map-based results, respectively. These results verified that the proposed method is feasible to determine the SIC profiles in situ with a major advantage that allows both probes lowering multiple access PVC-tubes at the field scale.

► Two probes run in a common access tube in situ for frozen soil measurement. ► Accurate and nondestructive method for determining soil ice content in situ. ► Profiling soil ice content, total and liquid soil water contents in depth.