Abstract
Several studies have demonstrated the potential of actively heated fiber optics (AHFO) to measure soil water content (SWC) at high spatial and temporal resolutions. This study tested the feasibility of the AHFO technique to measure soil water in the surface soil of a crop grown field over a growing season using an in-situ calibration approach. Heat pulses of five minutes duration were applied at a rate of 7.28 W m−1 along eighteen fiber optic cable transects installed at three depths (0.05, 0.10 and 0.20 m) at six-hour intervals. Cumulative temperature increase (Tcum) during heat pulses was calculated at locations along the cable. While predicting commercial sensor measurements, the AHFO showed root mean square errors (RMSE) of 2.8, 3.7 and 3.7% for 0.05, 0.10 and 0.20 m depths, respectively. Further, the coefficients of determination (R2) for depth specific relationships were 0.87 (0.05 m depth), 0.46 (0.10 m depth), 0.86 (0.20 m depth) and 0.66 (all depths combined). This study showed a great potential of the AHFO technique to measure soil water at high spatial resolutions (<1 m) and to monitor soil water dynamics of surface soil in a crop grown field over a cropping season with a reasonable compromise between accuracy and practicality.
Highlights
Soil water is an essential component of many hydrological, climatological and environmental processes
It is important to note that the calibration accuracy was not affected over time; no significant trends and or changes were observed in root mean square errors (RMSE) values irrespective of the calibration routine. this might be due to the less exposure of the distributed temperature sensing (DTS) instrument to extreme temperature fluctuations
This study investigated the feasibility of the actively heated fiber optics (AHFO) technique to measure soil water in the surface soil of a crop grown field over a growing season using an in-situ calibration approach
Summary
Soil water is an essential component of many hydrological, climatological and environmental processes. SWC varies greatly in space and time due to local (soil properties, topography and vegetation) and non-local (climate) factors influencing it at different intensities at various spatial and temporal scales [5,6,7,8,9,10]. The advancement of soil water measurement has limited mostly to point scale using the point–based sensors (e.g., time domain reflectometry [TDR], frequency domain reflectometry [FDR] and capacitance probes) and at large scales using the remote sensing [11]. The scale of soil water measurement is often different from the scale of modeling and this has resulted in a mismatch between the observations and simulations [12,13]. Modelling of hydrological dynamics has improved significantly, measurement capability has not kept pace at intermediate spatial
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