慕士塔格地区大气水汽氢氧稳定同位素季节内变化特征及影响因素分析

慕士塔格地区位于青藏高原西北部,常年受西风影响。为了更清楚地认识西风水汽来源和局地蒸发过程对区域水循环过程的影响,利用2017年7月26日—2017年11月6日和2018年7月30日—2018年12月10日在慕士塔格西风带环境综合观测研究站的监测数据,分析了地表大气水汽氢氧稳定同位素组成和相关局地气象要素的变化特征及其相关关系。研究发现:慕士塔格地区水汽中δ¹⁸O、d-excess与局地温度和比湿呈现明显的小时变化、日变化和季节变化;水汽δ¹⁸O值与温度的显著正相关关系在不同时间尺度稳定存在;在小时和日尺度上,水汽δ¹⁸O值与比湿呈现对数关系;后向轨迹追踪表明,西风将西伯利亚和北大西洋及慕士塔格周围地区的水汽传输至观测站点;当水汽自地中海和北大西洋长距离传输至慕士塔格时,水汽δ¹⁸O显著降低可达约7‰,d-excess会显著增大;该地区水汽稳定同位素组成的季节变化特征与降水稳定同位素组成的季节变化特征一致。研究内容初步揭示了青藏高原西风传输水汽稳定同位素变化的主要影响因素,可为区域水循环研究提供必要...     

云南丽江台OSG-066重力潮汐观测结果及应用

基于云南丽江台超导重力仪OSG-066超过5 a的连续重力潮汐观测资料，获取高精度潮汐参数并构建地方重力潮汐模型，为丽江地区精确重力潮汐改正提供参考。研究9个全球海潮模型在丽江台的重力影响改正有效性，用时域内回归分析法和频域内小波分析法分别研究大气重力导纳值的变化特征，并利用观测潮汐数据估算自由核章动本征参数。结果表明，9个海潮模型在丽江台的重力影响改正效果基本一致，NAO.99b模型的改正精度较高；大气重力导纳值在时域和频域内均显示出较为明显的季节性变化特征，且与降雨量变化存在负相关关系。自由核章动本征周期为431.5(411.2, 454.0)恒星日，品质因子为 -2 796。     

青藏高原大气CH_(4)源汇及其浓度时空变化特征研究进展北大核心CSCD

Methane（CH4）is regarded as the second most important greenhouse gas after carbon dioxide（CO2）. Under the warming and wetting of the climate,the Qinghai-Tibet Plateau may become a potential carbon source. To achieve the 1. 5 ℃ and 2 ℃ temperature control targets of the Paris Agreement,it is necessary to accurately estimate the remaining carbon emission space in the future. Therefore,an accurate understanding of the source and sink functions,spatial-temporal changes and mechanisms of atmospheric CH4 in the Qinghai-Tibet Plateau is of great practical significance to predict and cope with warming and help the government make scientific deci⁃ sions on energy conservation and emission reduction. This paper summarizes the existing research progress from the following three aspects：observation method of atmospheric methane,source and sink of methane,and the spatial-temporal variation of the atmospheric CH4. The results show that the observations of atmospheric CH4 on the Qinghai-Tibet Plateau are mainly ground-based observations and satellite remote sensing,lacking space-based observations,and AIRS has the best data quality among satellite products;Methane of the Qinghai-Tibet Plateau is mainly from natural sources,the main sources are wetlands,lakes and animal livestock,geological ac⁃ tivities,vegetation and permafrost are the uncertain CH4 sources. The sink of CH4 is mainly tropospheric hydrox⁃ yl radical and alpine meadow;The seasonal distribution of CH4 on the Qinghai-Tibet Plateau has a single-peak in summer,which is synchronized with the seasonal pattern of the Asian summer monsoon;The average rising rate of CH4 concentration on the Qinghai-Tibet Plateau is about 5~8 ng·g-1·a-1,which is greater than that in the sur⁃ rounding areas;The high value of CH4 concentration near the surface of Qinghai-Tibet Plateau appears in the middle part,and decreases gradually from the ground to the tropopause,but the decrease in the east and north of the plateau is greater than that in the southwest. In the future,three dimensional continuous observation of atmo⁃ spheric CH4 should be strengthened,satellite inversion algorithm and source sink analytical model should also be improved. In addition,we need to accurately quantify the spatial-temporal change process of atmospheric CH4 in the Qinghai-Tibet Plateau and reveal its change mechanism to provide a scientific basis for the future efficient emission reduction policies. © 2023 Chinese Journal of General Practitioners. All rights reserved.     

基于主成分分析的多能谱CT图像分析方法研究

基于光子计数探测器的能谱CT,可以同时采集多个能谱通道的投影数据,并获得相应能量范围内物质的吸收特征,可以有效应用于物质识别与材料分解。主成分分析是一种很好的多元数据分析技术,可以用于处理多能谱CT数据。本文分别在投影域和图像域对能谱CT数据进行主成分分析,并对分析结果做出系统比较。为了减少噪声的影响,提高能谱CT图像的彩色表征性能,提出双域滤波与像素值平方相结合的方法,用于含噪声的主成分图像去噪,然后将所选取的主成分图像映射到RGB颜色通道。实验结果表明,无论是在投影域还是图像域进行主成分分析,都可以获取清晰的CT图像,识别出物质的不同成分。相较于在图像域的主成分分析方法,在投影域进行主成分分析能够保留物质的更多细节,获取更清晰的彩色CT图像。