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【Objective】 Spring wheat and alfalfa and two crops widely grown by farmers in Northwestern China. A knowledge of their planting areas is important for agricultural management but challenging at regional scale. This paper investigates the feasibility of using air-born technologies to identify their areas at different growing stages. 【Method】 The studies were based on Sentinel-2 imagery acquired from the Qingtongxia Irrigation District, with which we developed a decision tree classification algorithm to identify spring wheat and alfalfa. Accuracy of the method was tested against ground-truth data. 【Result】 The accuracy of the model for identifying spring wheat and alfalfa in early April was 69% and 75%, respectively, due to the similarities of the canopies of the two plants. With the growth of the plants and increase in available data, the accuracy of the model improved gradually, with its accuracy for identifying the spring wheat and alfalfa exceeding 90% on 14th May. Using all five satellite imageries available by 13th May, the accuracy of the model for identifying spring wheat and alfalfa reached 94% and 97%, with their associated Kappa coefficient being 0.75 and 0.86, respectively. The estimated planting areas of the spring wheat and alfalfa in Qingtongxia Irrigation District was 24,000 hm2 and 2,000 hm2, respectively. The spatial distribution of spring wheat was complex, characterized by a large number of fragmented planting zones. 【Conclusion】 The decision tree classification method combined with the Sentinel-2 images can preliminarily identify spring wheat and alfalfa in early April. Its accuracy improves steadily as more data become available, with the accuracy exceeding 90% after the middle of May.

For the particular engineering-geological conditions and natural environment in permafrost regions, the highway has a high damage ratio during the operation. In warm and ice-rich permafrost regions, highway pavement and embankment have poor serviceability, which threatens driving the vehicle and safe operation. Traditional field surveys on highway damage cannot entirely, rapidly and precisely obtain the distress information along the whole road. In this paper, the Qinghai-Tibet Highway (QTH) pavement distress was investigated in 550-km-long permafrost regions based on the field surveys in 2014 and 2019 and the unmanned aerial vehicle (UAV) imagery. The type and damage ratio of distress were extracted by the remote sensing image classification method. The pavement roughness and embankment height were acquired by the spatial analysis of geographical information system. This paper provides a novel insight and efficient method for the distress investigation and exploration of distress formation in permafrost region, which can be applied in other similar engineering projects in the cold and inclement permafrost region. Furthermore, this paper also presents valuable and first-hand field data for evaluating highway serviceability and prevention of road damage during operation and maintenance stages. [ABSTRACT FROM AUTHOR]

The environmental damage caused by mining activities is often quantified by land use change, which is a good way to reveal the extent the environment being impacted on a spatial and temporal scale. In order to understand the impact of mining activities in the high cool-altitude areas on environment, a high-altitude open pit mine in Tianshan Mountain, Xinjiang Prefecture, was taken as the research object. Integrating the spectral characteristics and texture information of ground objects, the supervised classification method and object-oriented classification method were used to classify the Landsat 7/8 Satellite RS images which was obtained in the different years including 2000, 2005, 2010, 2015 and 2019, totally divided four periods. The accuracy of the classification results was verified, and the spatial distribution characteristics and temporal variation characteristics of land use were analyzed by GIS statistical analysis method, for the purpose to reveal the impact of mining activities on the special environment ranges. The results show that the classification accuracy of the supervised classification using SVM algorithm is as high as 95%. The intensity and direction of land use transfer in mining area are quite different before and after mining. The bare land and grassland are basically stable before mining, and the glaciers, snow and water are transferred to each other. After mining for a long time, the intensity of mutual transfer among various types increasing, the direction is diverse, and changes over a long time. By 2019, the land use in the mining area has basically returned to the level of 2000, the initial state, and the transfer of land use tends to a new dynamic balance. [ABSTRACT FROM AUTHOR]

A physical calculation model for the content of unfrozen water of silty clay was proposed with a consideration of freezing point. The freezing point of bulk water, capillary water and bound water was calculated. The freezing point of bulk water was assumed to be constant in the calculation. The Kelvin equation and the theory of water activity were used to calculate the freezing-point changes of the capillary and bound water during the volume decrease, respectively. The influence of soil-particle size on the freezing point was taken into account in the model. In the calculation, the unfrozen water content at a negative temperature was defined as the sum of the volume of capillary and bound water whose freezing point was lower than the given temperature. By using silty clay from the Qinghai-Tibet Plateau as an example, the results of the model calculations were validated by using the measured data from time-domain reflection and nuclear magnetic resonance. The calculations for four existing models as proposed by other scholars were listed for comparison with our model. The results show that the calculated results of our model are precise and reflect the hysteresis effect of the unfrozen water content during freezing and thawing. The model validated an order of freezing in soil: bulk water froze first, most capillary water froze next, and most bound water froze last. This paper explains the existence of unfrozen water from the perspective of freezing-point change and provides a theoretical basis for the calculation. [ABSTRACT FROM AUTHOR]