## 1 Introduction  
Vegetation plays an indicative role in global change and is an important part of Earth's ecosystem. It also plays an important role in the process of land surface energy exchange,the biogeochemical cycle, and the hydrological cycle, and it can characterize land cover changes to a certain extent [1; 2]. With the joint influence of climate change and human activities, the vegetation status in different periods will be affected, resulting in great differences in vegetation growth status between years [3; 4]. Since the beginning of the 21 st century, the degree of global vegetation greening has increased significantly, and China has contributed to nearly 25% of it, ranking first in the proportion of contribution [5]. This also contributes to the development of ecological governance in northwest China. The northwest is a region with the most widely distributed desertified and sandy land in China, and the continual ecological governance has led to the emergence of \"green\" in the region [6]. The Aksu region is located in the central and western parts of Xinjiang. It has a typical, warm-temperate arid climate, with sparse precipitation, large evaporation, and a dry climate. The desertification land area accounts for 77.08% of the total area, and the desertification land area accounts for 46.99%. It is one of the main wind-blown sand sources in southern Xinjiang [7] In order to combat the erosion of the land desertification and salinization, the Kokyar Greening Project was launched in Aksu, Xinjiang, in 1986 [8]. Over the past 36 years, cadres and the masses of all ethnic groups have worked together, and Kokyar, which was the source of sandstorms, is shaded with green trees. Additionally, taking this as the starting point, millions of acres of \"green seas\" have been bred in the deserts and barren beaches of southern Xinjiang [9]. Kokyar has changed from a cliff and a ravine that was once barren to a fragrant orchard with millions of acres of green trees. Aksu, which was once only 6 km away from the desert, was named the first \"National Forest City\" in northwest China. The United Nations also listed this green legend as one of the \"Global 500 Best Places\". However, the understanding of the improvement of the vegetation ecological quality in the Kokyar Project Area in recent decades remains qualitative, and there is a lack of temporal and spatial variation characteristics and driving mechanisms for comprehensively evaluating the vegetation ecological quality in this area from a quantitative and digital perspective. Remote sensing is currently the most powerful method with which human beings can rapidly realize global- or regional-scale Earth observation. Due to its high temporal and spatial continuity, it is considered to be one of the important means for carrying out vegetation ecological quality research [10]. To date, scholars have used remote-sensing data to create a variety of remote-sensing indices to quantify the status of vegetation ecology, such as the normalized difference vegetation index (NDVI) [11], the enhanced vegetation index (EVI) [12], net primary productivity (NPP) [13], land use and land cover (LULC) [14], and the remote-sensing ecological index (RSEI) [15]. Limited by the spatial resolution of satellite data and the small amount of single satellite data, previous studies on the changes in the temporal and spatial distribution of the vegetation ecological quality in the desert areas of Xinjiang focused on the whole area of Xinjiang or on regional-scale areas such as southern and northern Xinjiang. However, the research on small areas, particularly on the Kokyar Project Area, has rarely been conducted using high-spatial-resolution remote-sensing data. With the rapid development of space-based remote-sensing technology, great progress in spectral resolution, spatial resolution, and time resolution has been made with the use of satellite image data; this has enabled hyperspectral, high-spatial-resolution, all-time, all-weather, and real-time Earth observations.