Application of cosmic-ray neutron sensing to monitor soil water content in an alpine meadow ecosystem on the northern Tibetan Plateau

Abstract

Keywords: CRNS Soil moisture Alpine meadow Tibetan Plateau s u m m a r y Cosmic-ray neutron sensing (CRNS) is a new method for continuously monitoring mean soil water content (SWC) on a hectometer scale. To evaluate the application and accuracy of the method for SWC observation in an alpine meadow ecosystem (AME), we installed the CRNS in a flat meadow near the Naqu prefecture on the northern Tibetan Plateau. We collecting soil samples and applying the system by the oven-drying method. A weather station was also installed near the CRNS for monitoring basic meteorological variables and the soil temperature and water content at various depths. Three Em-50 instruments for monitoring SWC and soil temperature were buried in three sub-quadrats northwest, northeast and southeast of the CRNS at distances of 460, 370 and 373 m, respectively, to observe the variation of SWC at the various depths. The footprint of the CRNS for SWC observation in the meadow was about 580 m, and the mean measuring depth was about 31 cm according to the general calculation equations. The reference neutron flux for dry soil (N 0 ) had a mean and coefficient of variation of 8686 and 3%, respectively, and remained substantially invariant throughout the measuring period. The five SWCs from the independent field samples almost passed through the SWC trend of the CRNS, the root mean square error (RMSE) was 0.011 m 3 m À3 for the CRNS and oven-drying method. The time series of SWC measured by the CRNS agreed well with the mean SWC series to a depth of 20 cm measured by the weather station. The trend of SWC measured by the Em-50s generally agreed with the trend of SWC measured by the CRNS, but some values and variations of SWC differed between the Em-50s and CRNS data. Because of the good agreement between the CRNS and independent field samples, we suspect that this disagreement is due to an insufficient representativeness of point observations and the distances of the points from the CRNS. The diurnal variation of hourly SWC from the CRNS was sinusoidal during a dry period, peaking at 11:00 and was minimum at 18:00 (Beijing time), with a range of 1%. Overall, the CRNS measured SWC in the AME with an acceptable accuracy, providing a scientific basis for the promotion and application of the CRNS in high, cold ecosystems.

Spatial simulation of soil‐water content in dry and wet conditions in a hectometer‐scale degraded alpine meadow

“…Other soil properties also tended to vary with depth (Figure ). BD, GSC, and pH increased, and CP and OCD decreased with depth, but particle composition had no obvious variation, indicating that the soil texture was spatially homogeneous in this area, which is consistent with the results obtained by Zhu et al (). The CVs of the BD, CP, K s , GSC, OCD, and clay, silt, and sand contents (Clay, Silt, and Sand) ranged between 0.11 and 0.98 (Table ), all indicating moderate variability.…”

“…SWC studies at hectometer scales in this area are rare but are needed to fill the gap between point and regional scales and to provide a bridge for scale transformation. Zhu et al (), Zhu et al (), and Zhu, Cao, Shao, and Liang () studied the temporal variation in SWC at a hectometer scale using a cosmic‐ray neutron probe to measure SWC, but the mean SWC could not reflect the spatial variability. The SWC in alpine meadows on the TP has also been simulated using SHAW and CoupModel (Chen et al, ; Zhang et al, ).…”

Cosmic‐ray Neutron Rover Surveys of Field Soil Moisture and the Influence of Roads

“…The CRNS technology makes use of the extraordinarily high sensitivity of cosmicray neutrons to hydrogen nuclei and measures the concentration of epithermal neutrons above the soil surface. Since its introduction, the CRNS technology has quickly established itself in the field of hydrological observations (Andreasen et al, 2017) and is now used for soil moisture monitoring by many research groups worldwide (e.g., Bogena et al, 2013;Franz et al, 2013a;Peterson et al, 2016;Schrön et al, 2017;Zhu et al, 2016).…”

Calibration and Validation of the Cosmic Ray Neutron Rover for Soil Water Mapping within Two South African Land Classes

“…Cosmic ray neutrons are high-energy subatomic particles, which originate in outer space [12]. These particles penetrate through the Earth's magnetic field and into the atmosphere [22]. Cosmic ray neutrons interact with atmospheric nuclei, which results in a cascade of secondary cosmic rays (epithermal neutrons), which move towards the land surface and encounter a denser mass when they reach the soil [23].…”