地基微波遥感评估黄河源区草原下垫面土壤冻融过程研究

土壤冻融过程对气候变化非常敏感,如何准确监测土壤冻融过程具有重要的科学意义。利用2017年6月至2018年6月中国科学院若尔盖高原湿地生态系统研究站玛曲观测场地基微波辐射计观测数据、浅层土壤温度和近地面气温数据,通过构建归一化极化比值冻结因子、极化差值冻结因子、组合水平极化差值冻结因子和组合垂直极化差值冻结因子等不同土壤冻结因子,评估了黄河源区草原下垫面土壤冻融过程。结果表明：L波段微波辐射计监测土壤冻融状态的结果与近地面气温和浅层土壤温度表征的土壤冻融过程基本一致。当入射角为50°时,归一化极化比值冻结因子和极化差值冻结因子与实测数据的一致性分别达到83.6%和82.8%。每种冻结因子具有明显的季节性变化,四种冻结因子在春季时的准确度低于夏、秋、冬三个季节。归一化后的相对冻结因子的标准差在秋季最大,可达0.3;在冬季和夏季最小,值小于0.2。在土壤发生冻结和融化转换时,垂直极化和水平极化下的亮温同时下降,其差值较完全冻结或者完全融化时的亮温差大。研究结果可为微波遥感监测土壤冻融过程提供技术参考。     

非饱和网纹红土比例加载特性研究

本文利用应力控制式全自动GDS静三轴仪对含水率相同、干密度相同重塑网纹红土进行分级加载条件下不同恒应力比路径、不同基质吸力的三轴固结排水试验,研究了非饱和网纹红土比例加载特性。研究结果表明：在比例加载条件下,非饱和网纹红土的基质吸力平衡过程中,反压排水量有一个明显的转折点,此转折点可作为判断基质吸力是否到达平衡的时间点;通过比较不同基质吸力下的轴向应变和时间的关系曲线发现,基质吸力的增加引起轴向应变增加;在偏应力保持不变的条件下,基质吸力的增加没有引起轴向应变的明显增加;不同基质吸力下的偏应力和净平均应力呈直线关系,其斜率近似为恒应力比;提出一种可以预测非饱和网纹红土比例加载条件下的径向应变的方法。     

联合反演模型中相对权比的约束反演

为确定联合反演模型中的相对权比,提出根据数据先验信息对相对权比进行一定约束,并将相对权比同其他模型参数一并作为未知参数参与反演的方法。数值实验表明,当先验信息可靠时,运用该方法可以获得较好的结果。     

一定厚度的油膜对海浪的抑制模型研究

本文结合海浪谱的作用量平衡方程,给出了一定厚度油膜对海浪的抑制模型,该模型不仅与油膜的物理参数有关,而且与环境参数有关。文中开展了抑制比对这些参数的敏感性分析,数值模拟结果表明:动力学粘性,表面/界面弹性、油膜厚度、油膜覆盖率等参数对抑制比的影响较大,但油膜的其他物理学参数如:密度、表面/界面张力,表面/界面粘度几乎对抑制比不产生影响;而且,文中还发现风速和风向对抑制比的影响较大。一般情况下,油膜对雷达回波信号的抑制,只需考虑油膜对海浪的抑制作用;但对厚乳化溢油而言,还应考虑到介电常数的减小对雷达回波信号的抑制。将本文建立的抑制比模型所得结果与墨西哥湾溢油事故期间的15景ENVISAR ASAR影像所得抑制比结果进行了比较。     

Characterizing the influence of tide on the physico-chemical parameters and nutrient variability in the coastal surface water of the northern Bay of Bengal during the winter season

The spatial distribution of physico-chemical parameters(sea surface temperature(SST), p H, sea surface salinity(SSS), dissolved oxygen(DO) and Secchi depth) along with filterable nutrients(dissolved inorganic nitrate(DIN),dissolved inorganic phosphate(DIP) and reactive silicate(DSi)) are measured in the winter months of November,December, January and February for four consecutive years from 2009–2010 to 2012–2013 on the shallow continental shelf(20 m bathymetry) of the coastal waters(up to 18 km away from shoreline) of the northern Bay of Bengal(n Bo B) during the highest high tide(HHT) and lowest low tide(LLT) hours for the first time. The variability of the coastal biogeochemical environment is assessed during the HHT and LLT hours and for this purpose, seawater samples are collected from seven different locations of a transect in the coastal region. Physicochemical parameters(except SST) show significant difference in magnitude during the HHT and LLT hours respectively. p H, SSS and DO are found to increase in the HHT hours and vice-versa. The data reveal that during the LLT hours, a relative increase of freshwater input in the n Bo B can have elevated the nutrient concentration compared with that observed during the HHT hours. The ratio of nutrient concentration is found to deviate significantly from the Redfield ratio. The abundance of DIP is much higher compared with that of DIN and DSi.The anthropogenic sources of DIP from the upstream flow(especially the domestic effluent of several metropolises) can be mainly attributed behind such an observation. In order to characterize and establish the trend of such variation in such an important bio-climatic region, long-term and systematic ecosystem monitoring in the coastal water of the n Bo B northern Bay of Bengal should be carried out throughout the year.     

Resolution of Seamount Geoid Anomalies Achieved by the SARAL/AltiKa and Envisat RA2 Satellite Radar Altimeters

The resolution of seamount geoid anomalies by the SARAL/AltiKa Ka-band radar altimeter is compared with the Envisat RA2 Ku-band altimeter using cross-spectral analysis of exact-repeat profiles. Noise spectra show white noise floors at root-mean-square levels around 8 mm per root-Hz for AltiKa and 19 mm per root-Hz for RA2, and are colored at wavelengths longer than a few km, with a spectral hump similar to that seen in Jason-2 data. The AltiKa noise level is lower than the RA2 noise level by more than one would expect from the ratio of their pulse repetition frequencies. Large outliers are present in data from both altimeters, always of one sign (range too long), and show little correlation with rain or other error flags. Seamount anomaly signal to noise ratios are 30 to 10 dB for AltiKa and 3 to 8 dB less for RA2, decreasing as seamount size decreases. Seamounts as small as 1.35 km tall are resolved by both instruments, with significantly better performance by AltiKa due to its lower noise level. If AltiKa can fly a geodetic mission, it will find many presently unknown seamounts.     

基于区域跟踪的增雨效果分析方法新探

在高炮催化区跟踪算法基础上,探究了选取等面积同心圆环作为对比区进行人影作业效果物理评估新方案,并给出了该方案适应性判断指标。选取垂直液态含水量和面雨量作为方案检验因子,分析了不同自然降水过程中,不同时间段"催化区"和"对比区"平均物理量的双比值和相对偏差等参量的变化;并以相似离散度为指标,分析该方法的适用范围,分析何种条件下自然降水的"催化区"和"对比区"变化比较一致且小于增雨效果。实验表明:不同自然降水过程中,"催化区"和"对比区"30 min平均垂直液态含水量变化以及3 h平均相对增雨均小于增雨效果,新方案可用于人工增雨效果分析。后提出将综合相似离散度作为判据,当其值大于0.2时,则不采用该方案,判据的增加明显改善了新方案评估效果。     

灌河口北部海域氮磷营养盐分布及富营养化评价

于2012年5月至2013年2月期间在灌河口北部海域取样,分析讨论了灌河口北部海域营养盐含量的时空变化及其影响因素、海域的富营养化水平和营养级类型。结果表明,整个调查期间,无机磷的含量相对较低,高N/P值显示磷可能成为该研究海域浮游植物生长的限制因子。调查海域近岸及附近海域营养指数E值大于1,处于富营养状态。营养级评价结果显示海域四个季节大多数站位处于磷中等限制潜在性富营养状态。无机氮含量较高,灌河口附近海域普遍超过第四类海水水质标准,其中夏秋季高于春冬季,是由于夏秋季陆源输送增大所致。     

GPS现代化后L2载波的数据质量分析

从L2C码的信号结构、多路径效应和信噪比3个方面对实际采集到的观测数据进行分析,结果表明,新的L2C码采用了新的设计结构,其多路径效应与C/A码的多路径效应较为一致,且L2载波的信噪比得到明显提高。然后利用L1载波和L2载波分别求解双差模糊度,实验结果说明,加载了L2C码的L2载波和L1载波计算双差模糊度的效果一致,较原未加载L2C码的载波在模糊度解算效率上有显著的提高。     

抛物线拟合的高斯投影长度比计算方法

针对传统的高斯投影长度比计算公式存在的次数高、参数多、计算过程复杂等不足,该文提出利用抛物线拟合法计算高斯投影长度比。首先,对高斯投影规律进行全面分析,得出高斯投影长度比与距离中央子午线横坐标值的变化成抛物线关系。然后,以点在高斯平面直角坐标系中距离中央子午线的横坐标值为参数计算高斯投影长度比。实验结果表明,采用该文方法计算高斯投影长度比运算简便、精度高,与传统公式计算的长度比差值在整个高斯投影带均达百万分之一量级,对完善高斯投影长度变形规律的研究以及实际计算均具有一定的参考价值。