Suitability of Cosmic Ray Neutron Probe for Soil Moisture in Different Ecosystems During Rainy Season
Accurate measurement of soil moisture is key for research in multiple disciplines such as meteorology,ecology,hydrology,agriculture,etc.Soil moisture holds important application value in flood forecasting,drought warning,ecological restoration,irrigation management,and soil erosion prevention and control.Currently,soil water monitoring mainly focuses on the point scale(within 1 m2)and remote sensing large-scale(research units usually exceed 100 m2).It is necessary to develop soil moisture monitoring technologies that can accurately measure soil moisture content on a small scale and connect with larger-scale soil moisture monitoring technologies such as remote sensing.The Cosmic Ray Neutron Probe(CRNP)is a new method for measuring soil moisture by monitoring the number of neutrons near the Earth's surface;the measuring radius in the horizontal direction of the CRNP is 130-240 m depending on air humidity etc.The theoretical detection depth of the CRNP is about 12-76 cm.To evaluate the applicability of the CRNP for soil moisture monitoring in different ecosystems,this study,based on the data from the automatic soil moisture stations of the China Meteorological Administration measured by Frequency Domain Reflectometry(FDR),explores the depth of soil moisture monitored by the CRNP in three different ecosystems such as grassland,farmland and woodland during the rainy season(June to September).The results show that the effect monitored by the CRNP in grassland in 0-20 cm is the best,and that for farmland and woodland in 0-30 cm is the best.Compared with soil moisture data monitored by the SMAP(Soil Moisture Active and Passive)satellite remote sensing,the results of soil moisture measurement in farmland and forest ecosystems by the CRNP are less different from those of the FDR;however,for grassland ecosystems,the difference between the results of CRNP and remote sensing monitoring is smaller than that of the FDR,which may be related to the strong heterogeneity of grassland soil.After the occurrence of precipitation events exceeding 5 mm in grasslands,farmland,and woodlands,the soil moisture monitoring values of the CRNP all increase,indicating that this method can sensitively respond to precipitation events.A comparison of changes in soil moisture monitoring values between the CRNP and the automatic stations before and after precipitation events can find that the CRNP is easier to capture the regional water fluctuation changes than the point-scale automatic soil moisture station.The results can provide a scientific basis for the application of the CRNP in soil moisture monitoring in different ecosystems.
cosmic ray neutron probesoil moistureprecipitationmeasure depthsuitability
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