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【Objective】 Most channels in Hetao irrigation district have been linned in attempts to reduce seepage and ameliorate soil salinization, but there is lack of understanding of its efficacy at district scales. This paper is to fill this knowledge gap using remote sensing technologies. 【Method】 The analysis was based on Landsat8 multispectral satellite imageries, and saline-alkali soils in the irrigation district were automatically extracted using the ISODATA clustering method. A buffer zone wide d on both sides of each channel was identified using a spatial analysis method, saline-alkali area and the salinization index (φ) in which were statistically analyzed. 【Result】 Saline-alkali soil area decreased significantly on both sides of the channel after the lining, and spatial distribution of the saline-alkali soils is in a trapezoid-shape. From 2013-2016, the salt-alkali soils within the 500m proximal to the channels had reduced from 49.63% to 86.81%, depending on locations, while within the 1 000 m and 1 500 m adjacent to the channels, they had reduced from 47.95% to 95.06%, and from 54.56% and 95.68%, respectively. Soil texture will affect the change of saline-alkali land area, and the area of saline-alkali land decreases faster in the region with low soil clay. 【Conclusion】 ① Satellite remote sensing technology is feasible to evaluate the salt control effect of large-scale channel projects. ② The spatial distribution pattern of saline-alkali land changed from uniform distribution to aggregation distribution after canal lining. ③ The channel lining project effectively inhibited the soil salinization process on both sides of the saline-alkali land. ④ Soil texture indirectly affects the treatment effect of lining engineering. The treatment effect of lining engineering is more obvious in the area with lower soil clay.

Real-time and high-precision water level monitoring is crucial for the fields of hydrology, hydraulic engineering, and disaster prevention and control. The most prevalent method for measuring water level is through the use of water level gauges, which can be costly and have limited coverage. In recent years, Global Navigation Satellite System Reflectometry (GNSS-R) technology has emerged as a promising approach for water level monitoring due to its low cost and high coverage. However, a limitation of current GNSS-R technology is the extended time required to record signals, which hinders its potential for real-time application. This paper introduces a novel real-time water level monitoring method based on GNSS dual-antenna attitude measurement and develops a model to invert water level based on baseline vector. This method uses double-difference observations to eliminate errors caused by various factors, such as satellite and receiver clock, and ionospheric and tropospheric delay. To avoid the impact of detecting and correcting cycle slips during real-time operations, a single-epoch calculation method is introduced. In order to verify the stability and reliability of our method, field tests were carried out at Dongshahe Station in Beijing. We obtained water level data with a time resolution of 1 Hz through field experiments. Experimental data collected from 12 May to 8 June 2022 and from 4 July to 8 August 2022 showed good agreement with on-site water gauge measurements, with root mean square errors of 2.77 cm and 2.54 cm, respectively. Experimental results demonstrate that this method can achieve high-precision, high-temporal-resolution water level monitoring. [ABSTRACT FROM AUTHOR]

Most dams in China have been operating for a long time and are products of the economic and technical limitations at the time of construction. Due to decades of aging engineering and ancillary problems, these reservoirs pose great threats to the safety of local people and the development of the surrounding economy. In this study, the surface deformation information for the Banqiao Reservoir is monitored with the small baseline subset–synthetic aperture radar interferometry (SBAS-InSAR) method using 80 Sentinel-1A images acquired from 3 January 2020 to 20 August 2022. Additionally, ground measurements from the BeiDou ground-based deformation monitoring stations were collected to validate the InSAR results. Based on the InSAR results, the spatiotemporal deformation features of the dam were analyzed in detail. The results show that the deformation in most areas, including the dam in the study area, is relatively stable, and the regional deformation velocity of the Banqiao Reservoir dam and other hydraulic engineering facilities varies between −1 mm/y and −4 mm/y. The Ru River area has a relatively obvious subsidence trend, and the maximum subsidence velocity reaches 30 mm/y. The InSAR monitoring results are consistent with the change trend in the BeiDou ground-based deformation measurement results. The monitoring results for the reservoir dam area provide a reference for local sustainable development and geological disaster prevention. [ABSTRACT FROM AUTHOR]

Large-scale surface water mapping not only helps us protect, utilize and manage water resources but also contributes to the understanding of climate change and the hydrologic cycle. A recent study showed that a multilayer perceptron (MLP) neural network is an effective method to identify various surface water types from Landsat 8 Operational Land Imager (OLI) satellite imagery. We use this method to produce a surface water map of China for 2015 (SWMC-2015) at a 30 m pixel size. The accuracy of SWMC-2015 was assessed with a set of random water and not water validation points. The strengths and limitations of SWMC-2015 include: the SWMC-2015 clearly shows the major lake clusters and river networks with high mapping accuracy and the overall accuracy and kappa coefficients of SWMC-2015 are 90% and 0.78, respectively. The accuracy of SWMC-2015 can be improved from perspective of training samples representation, verification sample seasonal fluctuation and mixed pixel. The SWMC-2015 is available for free download on the remote sensing of global change website (). [ABSTRACT FROM AUTHOR]