Feasibility of irrigation monitoring with cosmic-ray neutron sensors

[摘要] Accurate soil moisture (SM) monitoring is key inirrigation as it can greatly improve water use efficiency. Recently,cosmic-ray neutron sensors (CRNSs) have been recognized as a promising toolin SM monitoring due to their large footprint of several hectares. CRNSs alsohave great potential for irrigation applications, but few studies haveinvestigated whether irrigation monitoring with CRNSs is feasible, especiallyfor irrigated fields with a size smaller than the CRNS footprint. Therefore,the aim of this study is to use Monte Carlo simulations to investigate thefeasibility of monitoring irrigation with CRNSs. This was achieved bysimulating irrigation scenarios with different field dimensions (from 0.5to 8 ha) and SM variations between 0.05 and 0.50 cm 3  cm −3 .Moreover, the energy-dependent response functions of eight moderators withdifferent high-density polyethylene (HDPE) thickness or additionalgadolinium thermal shielding were investigated. It was found that aconsiderable part of the neutrons that contribute to the CRNS footprint canoriginate outside an irrigated field, which is a challenge for irrigationmonitoring with CRNSs. The use of thin HDPE moderators (e.g. 5 mm) generallyresulted in a smaller footprint and thus stronger contributions from theirrigated area. However, a thicker 25 mm HDPE moderator with gadoliniumshielding improved SM monitoring in irrigated fields due to a highersensitivity of neutron counts with changing SM. This moderator and shieldingset-up provided the highest chance of detecting irrigation events,especially when the initial SM was relatively low. However, variations in SMoutside a 0.5 or 1 ha irrigated field (e.g. due to irrigation ofneighbouring fields) can affect the count rate more than SM variations dueto irrigation. This suggests the importance of retrieving SM data from thesurrounding of a target field to obtain more meaningful information forsupporting irrigation management, especially for small irrigated fields.

[学科分类] 再生能源与代替技术