ISPRS International Journal of Geo-Information / Extraction of terraces on the loess plateau from high-resolution DEMs and imagery utilizing object-based image analysis

Terraces are typical artificial landforms on the Loess Plateau, with ecological functions in water and soil conservation, agricultural production, and biodiversity. Recording the spatial distribution of terraces is the basis of monitoring their extent and understanding their ecological effects. The current terrace extraction method mainly relies on high-resolution imagery, but its accuracy is limited due to vegetation coverage distorting the features of terraces in imagery. High-resolution topographic data reflecting the morphology of true terrace surfaces are needed. Terraces extraction on the Loess Plateau is challenging because of the complex terrain and diverse vegetation after the implementation of “vegetation recovery”. This study presents an automatic method of extracting terraces based on 1 m resolution digital elevation models (DEMs) and 0.3 m resolution Worldview-3 imagery as auxiliary information used for object-based image analysis (OBIA). A multi-resolution segmentation method was used where slope, positive and negative terrain index (PN), accumulative curvature slope (AC), and slope of slope (SOS) were determined as input layers for image segmentation by correlation analysis and Sheffield entropy method. The main classification features based on DEMs were chosen from the terrain features derived from terrain factors and texture features by gray-level co-occurrence matrix (GLCM) analysis; subsequently, these features were determined by the importance analysis on classification and regression tree (CART) analysis. Extraction rules based on DEMs were generated from the classification features with a total classification accuracy of 89.96%. The red band and near-infrared band of images were used to exclude construction land, which is easily confused with small-size terraces. As a result, the total classification accuracy was increased to 94%. The proposed method ensures comprehensive consideration of terrain, texture, shape, and spectrum characteristics, demonstrating huge potential in hilly-gully loess region with similarly complex terrain and diverse vegetation covers.(VLID)219512

Envelope-Based Variable-Gain Control Strategy for Vibration Suppression of Solar Array Using Reaction Wheel Actuator

The orbital operation of spacecraft can excite the long-drawn and low-frequency vibration of the solar array, which is prone to affecting the task execution of the system. To address this issue, an envelope-based variable-gain control strategy is proposed to suppress vibration of the solar array using the reaction wheel (RW) actuator. The RW actuator is individually mounted on the solar array to provide reaction torque through the speed change of its rotor. The governing equation of motion of the solar array actuated by a RW actuator is deduced with the state space representation. The control relation between the measured bending moment and the rotational speed of the RW actuator with the constant-gain coefficient is firstly developed and demonstrated in numerical simulation. Changing the gain coefficient to be inversely proportional to the envelope function of vibration, a variable-gain control strategy is proposed to improve the damping effect of the RW actuator. Simulation results show that the vibration suppression performance of the RW actuator is improved compared to the constant-gain control. As the actual on-orbit natural frequency of the solar array is not always exactly known, the robustness of the control system is analyzed for the deviation between the estimated and the actual natural frequency values. The proposed variable-gain control is also experimentally verified using a simplified elastic plate model. Experimental results indicate that the vibration attenuation time is decreased to 29.1% and 50.22% compared to the uncontrolled and the constant-gain controlled states, respectively

Effect of urban tourist satisfaction on urban macroeconomics in China: A spatial panel econometric analysis with a spatial Durbin model.

Tourist satisfaction has always been a crucial research issue in the tourism economy. This paper utilizes the Spatial Durbin Model (SDM) to analyze the impact of urban tourism satisfaction on urban macroeconomics from a macro perspective, using quarterly data on tourist satisfaction in 35 large and medium-sized cities along with major urban macroeconomic variables. This study is quite distinct from previous research that focused on constructing a tourist satisfaction index and analyzing the influence factors of tourism satisfaction from the perspective of the micro-level internal composition of tourism. The empirical results show: Firstly, in respect of the impact of urban tourists' satisfaction on the GDP income of cities, the SDM and the SDM with a lagged first-order dependent variable (SDM_dlag) show that the short-term and long-term indirect effects of log-tourist satisfaction are significantly positive, indicating that city satisfaction has a significant positive spatial spillover effect on GDP growth in other cities; Secondly, in respect of the influence of urban tourist satisfaction on the cost of urban life in the SDM, the long-term direct and indirect effects of logarithmic satisfaction are significantly positive, implying, in the long run, that tourist satisfaction has a positive intraregional spillover effect and spatial spillover effect on urban living costs; Finally, the SDM_dlag for the regression of urban tourist satisfaction on the cost of urban daily life shows that the short-run direct and indirect effects of city tourist satisfaction are significantly negative, indicating that tourist satisfaction has intra-regional and spatial spillover effects, and its rise will reduce the cost of living expenses in local and other cities in the short term. Overall, we have further elucidated the role of different levels of urban tourist satisfaction in city macroeconomics from the spatial dimension, thereby enriching the existing research on tourist satisfaction to some certain extent

Progress of Digital Terrain Analysis on Regional Geomorphology in China

Regional geomorphological research is an important part of regional geography research. In recent decades, digital terrain analysis has been widely used in regional geomorphology research. However, due to the limitations of the classic neighborhood analysis algorithm, it is hard to realize the quantitative analysis on the macroscopic morphological features. To solve this problem, Chinese scholars had made a lot of explorations and innovations. An overall review was made in this paper on Chinese scholars' contribution to the DTA research on macro terrain morphology analysis, topographic feature analysis, tupu analysis, landform evolution, landform classification and mapping. The research review shows that Chinese scholars' researches are closely followed by international frontier. The digital terrain analysis in the Qinghai-Tibet Plateau, the Loess Plateau and the southwest karst area highlights the regional characteristics and advantages of geomorphology in China, and has had an important impact in the international academic session

A new extraction method of loess shoulder-line based on Marr-Hildreth operator and terrain mask.

Loess shoulder-lines are significant structural lines which divide the complicated loess landform into loess interfluves and gully-slope lands. Existing extraction algorithms for shoulder-lines mainly are based on local maximum of terrain features. These algorithms are sensitive to noise for complicated loess surface and the extraction parameters are difficult to be determined, making the extraction results usually inaccurate. This paper presents a new extraction approach for loess shoulder-lines, in which Marr-Hildreth edge operator is employed to construct initial shoulder-lines. Then the terrain mask for confining the boundary of shoulder-lines is proposed based on slope degree classification and morphology methods, avoiding interference from non-valley area and modify the initial loess shoulder-lines. A case study is conducted in Yijun located in the northern Shanxi Loess Plateau of China. The Digital Elevation Models with a grid size of 5 m is applied as original data. To obtain optimal scale parameters, the Euclidean Distance Offset Percentages between shoulder-lines is calculated by the Marr-Hildreth operator and the manual delineations. The experimental results show that the new method could achieve the highest extraction accuracy when σ = 5 in Gaussian smoothing. According to the accuracy assessment, the average extraction accuracy is about 88.5%, which indicates that the proposed method is applicable for the extraction of loess shoulder-lines in the loess hilly and gully areas

Spatial and temporal variations of ecosystem service values in relation to land use pattern in the Loess Plateau of China at town scale.

Understanding the relationship between land use change and ecosystem service values (ESVs) is the key for improving ecosystem health and sustainability. This study estimated the spatial and temporal variations of ESVs at town scale in relation to land use change in the Loess Plateau which is characterized by its environmental vulnerability, then analyzed and discussed the relationship between ESVs and land use pattern. The result showed that ESVs increased with land use change from 1982 to 2008. The total ESVs increased by 16.17% from US$6.315 million at 1982 to US$ 7.336 million at 2002 before the start of the Grain to Green project, while increased significantly thereafter by 67.61% to US$ 11.275 million at 2008 along with the project progressed. Areas with high ESVs appeared mainly in the center and the east where largely distributing orchard and forestland, while those with low ESVs occurred mainly in the north and the south where largely distributing cropland. Correlation and regression analysis showed that land use pattern was significantly positively related with ESVs. The proportion of forestland had a positive effect on ESVs, however, that of cropland had a negative effect. Diversification, fragmentation and interspersion of landscape positively affected ESVs, while land use intensity showed a negative effect. It is concluded that continuing the Grain to Green project and encouraging diversified agriculture benefit to improve the ecosystem service

Viral invasion, incubation, and outbreak under the normalized operation of urban systems: a spatial cognition-driven transmission model of infectious diseases

ABSTRACTLarge-scale epidemics, such as COVID-19, pose significant threats to human health and social stability due to their rapid and covert transmission, emerging as one of the main challenges to maintaining a well-functioning urban system. During the pandemic, the spatial transmission mechanisms and their influencing factors of infectious diseases have received as a central topic. Scholars concentrated on researching the phase of extensive dissemination and mandatory intervention, utilizing multiple datasets. However, there remains a notable gap in the investigation of virus spatial transmission mechanisms under normalized urban operations due to limitations in detection timeliness and data collection issues. Moreover, compared to various intervention strategies, the influence of human behavioral dynamics and spatial cognition remains understudied. The paper simulates invasion, incubation, and outbreak of the Omicron variant in Zhuhai City in 2022, validating the results against real-world epidemic data. By comparing spatial diffusion patterns under three levels of spatial cognition, it sheds light on the delayed impact of human spatial cognitive abilities on urban pandemic outbreaks and their influence on virus invasion orders. The simulation model and revealed diffusion mechanisms will provide important guidance for the proactive prevention and control of unpredictable large-scale epidemics in future urban systems