산악지형에서의 CRNP를 이용한 토양 수분 측정 개선을 위한 새로운 중성자 강도 교정 방법 검증 및 평가

Mesoscale soil moisture measurement from the promising Cosmic-Ray Neutron Probe (CRNP) is expected to bridge the gap between large scale microwave remote sensing and point-based in-situ soil moisture observations. Traditional calibration based on N₀ method is used to convert neutron intensity measured at the CRNP to field scale soil moisture. However, the static calibration parameter N₀ used in traditional technique is insufficient to quantify long term soil moisture variation and easily influenced by different time-variant factors, contributing to the high uncertainties in CRNP soil moisture product. Consequently, in this study, we proposed a modified traditional calibration method, so-called Dynamic-N₀ method, which take into account the temporal variation of N₀ to improve the CRNP based soil moisture estimation. In particular, a nonlinear regression method has been developed to directly estimate the time series of N₀ data from the corrected neutron intensity. The N₀ time series were then reapplied to generate the soil moisture. We evaluated the performance of Dynamic-N₀ method for soil moisture estimation compared with the traditional one by using a weighted in-situ soil moisture product. The results indicated that Dynamic-N₀ method outperformed the traditional calibration technique, where correlation coefficient increased from 0.70 to 0.72 and RMSE and bias reduced from 0.036 to 0.026 and -0.006 to -0.001 m³m^-3. Superior performance of the Dynamic-N₀ calibration method revealed that the temporal variability of N₀ was caused by hydrogen pools surrounding the CRNP. Although several uncertainty sources contributed to the variation of N₀ were not fully identified, this proposed calibration method gave a new insight to improve field scale soil moisture estimation from the CRNP.