Vegetation has long been recognized as an efficient way of preventing soil erosion; however, the effects of plants on gravity erosion are still broadly unknown, especially under heavy rain conditions. In order to evaluate their influences on gravity erosion, a series of rainfall simulation experiments were performed on a model of the loess gully sidewall, with a height of 1.5 m anda slope gradient of 70. The experiments were divided into two groups-bare land models (BLMs) and shrub land models (SLMs)-for inter-and intragroup comparison, respectively. The experimental results reveal that shrubs had different influences on the varied types of gravity erosion on the gully sidewall. The average landslide volume was 42% greater in the SLMs than in the BLMs, while the average avalanches and mudslide volumes in the SLMs were 50 and 36% less, respectively. Additionally, the average amount of erosion after rain in the SLMs was 33.17 × 10 3 cm 3 more than that in the BLMs, indicating that the vegetation may increase the occurrence of mass failure after a heavy rainfall. Compared with the anchoring effect of vegetation root, the change in soil water resulted from vegetation on the slope had a relatively great effect on aggravating the gravity erosion under heavy rainfalls. The experimental results suggest that the shrub restoration measures can be used to mitigate erosion in the areas experiencing frequent debris flows and hydraulic movements on the Loess Plateau, China.
Global land cover changed significantly in the last several decades due to strong climate warming and intensive human activities, and those changes greatly affected ecosystem services all over the world. Using CCI-LC land cover data from 1992 to 2020, the spatiotemporal characteristics of land cover change in China were investigated, and the annual ecosystem service values (ESVs) were estimated with the equivalent factor method. The results showed that: (1) The overall accuracy and Kappa coefficient of CCI-LC products in China were 71.1% and 0.65, respectively. (2) From 1992 to 2020, the area of cropland in China increased generally first before 2004 then decreased after 2008; the area of forest land decreased before 2003 then increased after 2015; the area of grassland and bare land consistently decreased; and the area of built-up land continuously increased, with a total increase of 113,000 km2. The primary characteristics of land cover transitions in China were the mutual conversion of cropland, forestland, and grassland as well as the continuous increase of built-up land. (3) Forest land was the most significant contributor of ESV in China, making 62.9% of the total ESV by multi-year average, followed by grassland (18.5%) and water (10.3%); the ESV was roughly high in the southeast China and low in the northwest. (4) The total ESV in China decreased generally before 2015 and got stable in the last five years. The hot spots with rising ESV were mainly concentrated in the western, northern and southwestern parts of China, while the cold spots with declining ESV were mainly concentrated in the economically developed eastern and southern China. (5) Cropland, forest land, grassland, and water were the positive contributors to ESV change in China, while built-up land and bare land were the negative contributors. The findings provide a theoretical foundation for China’s harmonized socioeconomic and environmental development.
The traditional target-dependent camera calibration method has been widely used in close-distance and small field of view scenes. However, in view of the field coordinate measurement in the large-scale monitoring area under the complex field environment, the standard target can hardly meet the requirements of covering most of the camera’s field of view. In view of the above problem, a stereo camera calibration method is studied, using the unmanned aerial vehicles (UAV) as feature points, combined with the high-precision position information measured by the real-time kinematic (RTK) positioning system it carries. The measured UAV coordinates are unified in World Geodetic System 1984 (WGS-84). Therefore, through several preset points, the measurement reference coordinate system which is the new world coordinate system we need can be established in any monitoring area, which greatly improves the flexibility of measurement. The experimental results show that the measurement accuracy of the proposed method can reach 0.5% in the monitoring area with a diameter of 100 m. The calibration method has a wide range of application and does not need the traditional standard target, and the measurement reference coordinate system can be established according to the actual needs. It is suitable for field spatial coordinate measurement in long-distance and complex terrain environment.
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