Integration of the MODIS Snow Cover Produced Into Snowmelt Runoff Modeling

Because of the difficulty of monitoring and measuring snow cover in mountainous watersheds, satellite images are used as an alternative to mapping snow cover to replace the ground operations in the watershed. Snow cover is one of the most important data in simulation snowmelt runoff. The daily snow cover maps are received from Moderate Resolution Imaging Spectroradiometer (MODIS), and are used in deriving the snow depletion curve, which is one of the input parameters of the snowmelt runoff model (SRM). Simulating Snowmelt runoff is presented using SRM model as one of the major applications of satellite images processing and extracting snow cover in the Ghara - Chay watershed. The first results of modeling process show that MODIS snow covered area product can be used for simulation and forecast of snowmelt runoff in Ghara - Chay watershed. The studies found that the SCA results were more reliable in the study area.     

升降轨PSInSAR观测反演沉降与水平向位移试验

In SAR观测的解算值为雷达视线向形变量,在具备多个方向独立观测的条件下可利用最小二乘方法反演垂直、东西甚至南北方向的形变量。由于难以同时获取上下、东西和南北3个方向上的独立观测值,因而可利用升降轨模式实现对垂向和东西方向移动量的估计。以PSIn SAR监测所获取的形变速率为观测值,利用二维简化模型求解地面沉降量和东西方向移动量。结果表明,研究区形变以沉降为主,水平方向移动微小,证明了升降轨PSIn SAR在地面沉降中的适用性和可靠性。     

A study of halo orbits at the Sun–Mars L1 Lagrangian point in the photogravitational restricted three-body problem

Photogravitational Restricted Three-Body Problem (PGRTBP) is considered and halo orbits are generated in the vicinity of the Sun–Mars L₁ Lagrangian point. Deviation of properties such as time period, size and velocity variation in the halo orbits with Sun as a source of radiation are discussed. With increase in solar radiation pressure, the halo orbits are found to elongate and move towards the Sun and the time period of the halo orbits is found to increase. The variation in the behaviour of invariant manifolds with change in radiation pressure is also computed and it is found that as the radiation pressure increases, the transition from Mars-centric path to heliocentric path is delayed. Certain implications of the velocity profile of the invariant manifolds are also discussed.     

Objective Analysis of Circulation Extremes During the 21 July 2012 Torrential Rain in Beijing

It has been reported that the heaviest rain event since 1951 hit Beijing on 21 July 2012 （henceforth referred to as the 721 case）.The frequency and extreme attributes of the large-scale circulation patterns observed during the 721 case are explored by using obliquely rotated T-mode principle component analysis （PCA） and reanalysis data from NCEP/NCAR.The occurrence frequency of the 721-type circulation during the summers of 1951-2012 is 10.9%,while the frequency of torrential rain under this type of circulation is 4.51%.Relative to other rainstorms with similar large-scale circulations during the study period,the 721 case is characterized by a more westward extension of the subtropical high over the western North Pacific,a stronger low-level jet in the lower troposphere over the south of Beijing,a larger amount of ambient precipitable water,and a stronger vertical wind shear over Beijing.Among the 621 days with the 721-type circulation during the study period,the 721 case ranks the 54th in terms of the 925-hPa low-level jet south of Beijing,the 209th in terms of the local vertical wind shear,and the 8th in terms of the local precipitable water.The 721 case is particularly extreme with respect to the 925-hPa low-level jet south of Beijing and local precipitable water.Cases with similar circulations and equal or greater values of the 925-hPa low-level jet south of Beijing and local precipitable water have occurred thrice during the summers of 1951-2012 （i.e.,once every 21 years）.     

Oligomeric products and formation mechanisms from acid-catalyzed reactions of methyl vinyl ketone on acidic sulfate particles

Methyl vinyl ketone (MVK) is a key first-generation product from atmospheric isoprene photo-oxidation, especially under high-NO_x conditions. In this work, acid-catalyzed reactions of gas-phase MVK with ammonium sulfate (AS), ammonium bisulfate (ABS), and sulfuric acid (SA) particles were investigated in a flow reaction system at relative humidity (RH) of 40 % and 80 %. Ultra-performance liquid chromatography with electrospray ionization time-of-flight mass spectrometry (UPLC/ESI-TOFMS) and gas chromatography-mass spectrometry (GC-MS) are utilized to identify particle-phase products for developing the reaction mechanisms. High-order oligomers such as dimers and tetramers were detected when ABS and SA particles were used, while no oligomeric products were found when AS particles were used. Particle-phase oligomeric products were formed via i) acid-catalyzed aldol reaction with or without dehydration and/or ii) acid-catalyzed hydration followed by oligomerization. Reactions on SA particles yield more abundant and higher-order oligomers up to hexamers than on ABS particles. Moreover, aldol reaction occurred only on SA particles, but hydration followed by oligomerization occurred in both ABS and SA particles. The high RH condition with the same type of acidic particles was found to favor hydration and facilitate the subsequent oligomerization, while the low RH condition with the same type of acidic particles was found to favor aldol reaction with dehydration (aldol condensation). Overall, the findings suggest acidic particles can facilitate the formation of high-order oligomers in the particle phase, with particle acidity and RH as key factors.     

边境城镇的产业演化及其机制研究

边境地区是我国的安全屏障和对外交流的门户,其产业演化深受地缘政治、国家和区域政策、当地发展条件等多元要素影响,嵌套于多尺度的社会经济发展框架中。在“一带一路”建设的背景下,边境地区的产业演化研究有着重要意义。本文将“一带一路”的重要节点边境城镇——云南省勐腊县作为案例区域,在进行实地调研和深入访谈的基础上,利用演化图谱、相关分析等方法,剖析了勐腊县的典型产业演化过程及多尺度要素作用下的产业结构演化机制。研究表明：勐腊县的橡胶、制糖和旅游三大典型产业均经历了萌芽、快速发展到成熟的过程;勐腊县作为边境县,产业发展大致可以分为起步、集聚和整合三个阶段;产业的演化受到了全球化进程、国家间关系、地缘政治博弈、国家开发政策、区域发展政策等多尺度因素的影响。随着“一带一路”中国—中南半岛经济走廊建设进一步提速,勐腊县获得了边境合作区、国家重点开发开放试验区等众多跨境合作发展新动能,迸发出新的活力。     

联合星载高光谱影像和堆栈集成学习回归算法的红树林冠层叶绿素含量遥感反演

红树林是世界上生产力最高、价值最高的湿地生态系统之一。冠层叶绿素含量CCC（Canopy Chlorophyll Content）作为红树林重要的生物物理参量,是估算其生产力和评价其健康状况的重要指标。本文利用珠海一号高光谱卫星（OHS）影像与Sentinel-2A多光谱数据计算传统植被指数与组合植被指数并构建了高维数据集,综合利用正态分布检验、最大相关系数法与变量重要性评价进行数据降维和变量优选;分别基于单一线性回归算法、机器学习回归算法和堆栈集成学习回归算法构建了红树林CCC遥感反演模型,探明北部湾红树林CCC的最佳遥感反演模型,验证OHS高光谱影像与Sentinel-2A数据反演红树林CCC的精度差异,评估SNAP-SL2P算法反演红树林CCC的适用性。研究结果表明：（1）通过数据降维和变量选择处理,从高维度OHS数据集选取了8个特征变量,其中RSI_（12,17）、DSI_（12,18）和NDSI_（6,12）组合植被指数对红树林CCC反演精度的贡献率较高;（2）联合OHS数据和最优堆栈GBRT集成学习回归模型（Score=0.999,RMSE=0.963 μg/cm²）的训练精度优于最优RF机器学习回归模型（RMSE降低了7.531 μg/cm²）,明显优于最优Lasso线性回归模型（RMSE降低了19.383 μg/cm²）;（3）在最优堆栈集成学习回归模型下,OHS数据反演红树林CCC的精度（R²=0.761,RMSE=16.738 μg/cm²）高于Sentinel-2A影像（R²=0.615,RMSE=20.701 μg/cm²）;（4）联合OHS和Sentinel-2A数据的最优堆栈集成学习回归模型反演红树林CCC的精度都明显优于SNAP-SL2P算法（R²=0.356,RMSE=49.419 μg/cm²）。研究结果论证了正态分布检验、最大相关系数法和基于XGBoost的特征选择方法有效降低了高维数据集的维度,并得到了最优特征变量;OHS数据的最优堆栈GBRT集成学习回归模型训练精度最高,是估算红树林CCC的最优反演模型;OHS和Sentinel-2A数据都能有效反演红树林CCC（R²均大于0.61）,而OHS数据的估算精度更高（R²大于0.75）;SNAP-SL2P算法不能有效反演红树林CCC（R²小于0.4）,且对红树林CCC数值存在系统性低估。     

历史文献中的气象记录与气候变化定量重建方法

历史文献记载是研究古气候变化的主要代用证据之一,对于定量重建过去数千年的气候变化序列具有独特价值.本文分析了中国历史文献中气象记录的特点及主要内容,重点梳理了利用各类记录定量重建气候变化序列的基本方法,并列举了通过多源记载集成、多时段记录衔接重建过去2000年中国东中部地区温度与干湿变化序列的校准案例;旨在为客观提取气候变化信息、获取高信度的气候变化数据和进一步发展利用文献记载定量重建气候变化序列的方法提供参考依据.主要认识是:1)历史文献中的气象记录主要有4类:天气、气象灾害、物候与区域气候特征及其影响记载;定量重建气候序列的基本方法有:回归分析、物理模型、分等定级、频次统计、类比分析等,但各类记录的来源、格式、连续性、详略与定量化程度不一,导致利用各类记录定量重建气候变化序列的方法也各不相同.2)对根据多源记载或不同方法反演的代用记录进行集成,利用回归分析、方差匹配、记录影响趋势剔除等校准技术,加强多源数据的相互插补方法研究,可解决古代气象记录的漏、缺记问题,是重建连续气候变化序列的主要途径.     

贵州六盘水炭质泥岩工程特性研究

六盘水的炭质泥岩跟普通泥岩相比具有特殊的工程特性,通过对该地区炭质泥岩物理力学特性的详细研究探讨,室内进行落锥法测定液限和塑限、击实试验、抗剪强度及压缩试验.研究试验结果表明：①炭质泥岩的可塑性强,遇水易软化崩解,强度变低;②炭质泥岩的压实性能受含水率的影响明显,干密度在含水率12.5％～15％时变化很大;③炭质泥岩的粘聚力在含水率小于11％时,随着含水率的增加而迅速减小,在11％～15％时变化小;④炭质泥岩的压缩沉降量在加荷载后较短时间内发生,在加压后能够很快压缩密实,达到较稳定的状态.