Search

The retrieval of soil moisture (SM) using the Global Navigation Satellite System-Reflectometry (GNSS-R) technique has become a prominent topic in recent years. Although prior research has reached a spatial resolution of up to 9 km through the Cyclone Global Navigation Satellite System (CYGNSS), it is insufficient to meet the requirements of higher spatial resolutions for hydrological or agricultural applications. In this paper, we present an SM downscaling method that fuses CYGNSS and SMAP SM. This method aims to construct a dataset of CYGNSS observables, auxiliary variables, and SMAP SM (36 km) products. It then establishes their nonlinear relationship at the same scale and finally builds a downscale retrieval model of SM using the eXtreme Gradient Boosting (XGBoost) algorithm. Focusing on the southern United States, the results indicate that the SM downscaling method exhibits robust performance during both the training and testing processes, enabling the generation of a CYGNSS SM product with a 1 day/3 km resolution. Compared to existing methods, the spatial resolution is increased threefold. Furthermore, in situ sites are utilized to validate the downscaled SM, and spatial correlation analysis is conducted using MODIS EVI and MODIS ET products. The CYGNSS SM obtained by the downscaling model exhibits favorable correlations. The high temporal and spatial resolution characteristics of GNSS-R are fully leveraged through the downscaled method proposed. Furthermore, this work provides a new perspective for enhancing the spatial resolution of SM retrieval using the GNSS-R technique. [ABSTRACT FROM AUTHOR]

Using AlN as nitrogen source, the gradient cemented carbide with β-phase free surface layer was fabricated in situ by one-step vacuum sintering. The β-phase free layer was explored by phase characterization, elemental-distribution analysis, microstructure and fracture observation. The results indicated that it was feasible to obtain β-phase free layer when utilizing AlN as the nitrogen source. The AlN decomposition fell appreciably to lower temperature in the presence of binder Co and Ni under vacuum sintering. The thickness of β-phase free layer could be tailored by controlling AlN contents, and the nitride former Al remained in the β-phase free layer. When applying nitrogen source AlN, the relative Ti content in the subsurface layer was lower than that with the conventional nitrogen source Ti(C,N) or TiN. By contrast, Co enrichment in the β-phase free layer is less significant than Ni as a result of higher solidification temperature. WC phases were much coarser averagely in the β-phase free layer than in the bulk, which was considered to be favorable for resisting against fracture. The β-phase free layer containing Al played a substantially improved role on the transverse rupture strength when AlN addition was 0.6 wt% and 1.2 wt%, while it is detrimental to the transverse rupture strength due to the formation of the intermetallic phase of Al and binder when AlN addition was 1.8 wt%. • It is feasible to use AlN as the nitrogen source for obtaining β-phase free layer. • The βFL thickness can be tailored by controlling the AlN contents. • Ti clustering is reduced in the subsurface layer when using nitrogen source AlN. • Co in the βFL is less enriched than Ni due to higher solidification temperature. • WC phases are coarser in the βFL, favorable for resisting against fracture. [ABSTRACT FROM AUTHOR]