基于多源遥感数据估算塔克拉玛干沙漠的输沙通量

As equilibrium state of dynamic interactions between sand particles and air flow, sand flux is one of the key parameters in studying aeolian landform of sand. Remote sensing could measure morphological characteristics in the fine-scale dune, but studies on estimating sand flux in the desert-wide scale by remote sensing are very rare. Sand flux estimated by remote sensing is defined as the product of dune migration speed and dune elevation difference. In this study, we try to use multi-source remote sensing data to invert sand flux in the Taklamakan Desert, wherein dune migration speed is the average at the yearly interval among achieving dates of image pairs from Landsat TMs after using the grayscale correlation technology of the COSI-Corr (Coregistration of Optically Sensed Images and Correlation) to compute dune displacements; and dune elevation difference is derived by the difference between the ICESat-1/2, SRTM DEM or TanDEM-X elevation. Sand flux is further decomposed into aeolian erosion flux on the windward slope and aeolian accumulation flux on the leeward slope, and the difference between the two is used to quantify ejection flux/deposition flux in the desert-wide scale. Finally, combined with some environmental factors, we try to analyze the temporal and spatial characteristics of dune migration speed and dune elevation difference, and study the spatial distribution of aeolian erosion flux and aeolian accumulation flux and temporal variation of ejection flux/deposition flux. The decomposition study of sand flux could be used to reveal the macroscopic law of aeolian movement in the Taklamakan Desert, and also provide theoretic and practical instructions for sand protection engineering.

输沙通量，作为沙粒与气流相互作用的平衡状态，是风沙地貌研究的关键参数之一。遥感可以测定小尺度沙丘的形态特征，而遥感估算沙漠尺度输沙通量的研究仍然很少。遥感估算的输沙通量定义为沙丘移动速度与沙丘高度差的乘积。本项目拟利用多源遥感数据反演塔克拉玛干沙漠的输沙通量，其中沙丘移动速度是通过COSI-Corr灰度相关技术得到的沙丘位移在Landsat TM像对获取日期的年间隔上的平均；沙丘高度差由ICESat-1/2、SRTM DEM或TanDEM-X的高度差值得到。输沙通量进一步分解为沙丘迎风坡上的风蚀通量和背风坡上的风积通量，而二者差值可用来量化沙漠尺度的喷射或沉降通量。最后，辅以环境因子分析沙丘移动速度、沙丘高度差的时空变化特征，解析风蚀通量、风积通量的空间分布和喷射或沉降通量的时间变化。输沙通量的分解研究有助于揭示塔克拉玛干沙漠风沙运动的宏观规律，也可为防沙工程提供理论和实践上的指导。

在世界各地，沙量平衡的变化可以重塑沙漠景观和引发沙丘入侵。由于床沙特征的空间异质性和野外测量的难达到，量化一个沙漠的沙量平衡是富有挑战性的。中国沙漠有着640.6×103 km2的总面积和各种床沙演替，是研究床沙行为的理想场地。本项目使用卫星高度计、全球高度模型和许多光学影像量化了中国沙漠尺度的沙量平衡。研究发现，在完整ICESat任务期内，中国沙漠的沙量平衡为-1.27±0.01 m2 yr-1（风蚀），显示出一个由风蚀到堆积向北的空间过渡。不同于单独沙漠的以往认知，古尔班通古特沙漠（0.98±0.01 m2 yr-1）和乌兰布和沙漠（0.28±0.05 m2 yr-1）有着显著的堆积，而毛乌素沙地（-1.40±0.04 m2 yr-1）有着明显的风蚀。本项目证实了中国沙漠内沙量平衡的空间转换，而乌兰布和沙漠、库布其沙漠和科尔沁沙地的堆积表面却有着时间转换。在接下来的几年，当ICESat-2和ICESat地面轨迹交叉点足够多的时候，本项目的研究方案可以很容易地部署到人迹罕至和数据缺乏的其他沙漠中。