Monitoring the water balance of Lake Victoria, East Africa, from space

Using satellite gravimetric and altimetric data, we examine trends in water storage and lake levels of multiple lakes in the Great Rift Valley region of East Africa for the years 2003–2008. GRACE total water storage estimates reveal that water storage declined in much of East Africa, by as much as , while altimetric data show that lake levels in some large lakes dropped by as much as 1–2 m. The largest declines occurred in Lake Victoria, the Earth’s second largest freshwater body. Because the discharge from the outlet of Lake Victoria is used to generate hydroelectric power, the role of human management in the lake’s decline has been questioned. By comparing catchment water storage trends to lake level trends, we confirm that climatic forcing explains only about 50decline. This analysis provides an independent means of assessing the relative impacts of climate and human management on the water balance of Lake Victoria that does not depend on observations of dam discharge, which may not be publically available. In the second part of the study, the individual components of the lake water balance are estimated. Satellite estimates of changes in lake level, precipitation, and evaporation are used with observed lake discharge to develop a parameterization for estimating subsurface inflows due to changes in groundwater storage estimated from satellite gravimetry. At seasonal timescales, this approach provides closure to Lake Victoria’s water balance to within . The third part of this study uses the water balance of a downstream water body, Lake Kyoga, to estimate the outflow from Lake Victoria remotely. Because Lake Kyoga is roughly 20 times smaller in area than Lake Victoria, its water balance is strongly influenced by inflow from Lake Victoria. Lake Kyoga has been shown to act as a linear reservoir, where its outflow is proportional to the height of the lake. This model can be used with satellite altimetric lake levels to estimate a time series of Lake Victoria discharge with an rms error of about .     

城市热岛的遥感研究进展

系统总结了应用遥感技术开展城市热岛研究的数据、方法与成果。对国内外学者有关城市热岛的形态结构、过程变化及成因分析等方面的研究内容进行了较为详细的评述，在此基础上，对未来城市热岛遥感研究的方向进行了展望。     

Relationships among water column toxins,cell abundance and chlorophyll concentrations during Karenia brevis blooms

The assumptions that Karenia brevis cell abundance and brevetoxin concentrations are proportional and that cell abundance and chlorophyll are related were tested in a 3-year field study off the west coast of Florida. The relationship between K. brevis cell abundance and brevetoxins (PbTx-2+PbTx-3) in whole water samples was strong (R²=0.92). There was no significant difference between the brevetoxin concentrations in whole water and the >0.7 μm particulate fraction. Only 7% of the total brevetoxin concentration was measured in the <0.7 μm (cell free) filtrate. The relationship of K. brevis cell abundance >5000 cells L⁻¹ with chlorophyll for all cruises and at all depths was robust (R²=0.78). These data substantiate the use of chlorophyll as a proxy for K. brevis cell abundance and K. brevis cell abundance as a proxy for brevetoxins during blooms. The ratios of the brevetoxins, PbTx-2:PbTx-3, was significantly higher in surface water than in bottom water. This information in conjunction with K. brevis growth rates may provide a useful indicator for determining the physiological state of the bloom over time.     

2007年8月大连地区一次暴雨过程特征分析

运用常规天气图资料,并根据地面自动站和多普勒雷达等资料,综合分析了2007年8月10－12日大连地区暴雨天气过程。结果表明：地面中尺度气旋的生成和发展是产生大暴雨的动力条件,低空急流的建立为暴雨产生提供了大量水汽,稳定的高压坝是暴雨落区在大连出现的必要前提。     

海洋资料浮标姿态信息测量技术研究现状及发展趋势

海洋资料浮标在海洋环境监测、预警预报、防灾减灾、资源开发、海上交通、渔业生产、军事活动保障等方面具有重要作用,是海洋立体监测体系的重要组成部分。世界主要沿海国家和国际组织都极为重视海洋浮标技术的发展。海上观测过程中,浮标随风、浪、流等作用产生复杂运动。浮标复杂运动的精确观测离不开浮标姿态信息测量技术的发展。浮标姿态信息,不仅是浮标及其搭载设备工作安全性可靠性评价的重要参考,也是浮标测量数据实时精准校正的重要保障。因此,浮标姿态测量技术具有重要的研究价值和应用价值。文章从工程实际的技术需求出发,对浮标姿态信息测量技术的研究现状、技术难点以及发展趋势等方面进行了梳理和总结,以期对研发新一代智能浮标观测技术提供有益启发和借鉴。     

Analysis of Thermal Infrared Anomalies for the April 16, 2013 MW7.8 of Khash, Iran Earthquake

After using the "Time-Frequency Relative Power Spectrum" (T-F RPS) method based on the China Geostationary Meteorological Satellite (FY-2C/FY-2E) infrared remote sensing brightness temperature data processing, we rapidly and accurately extracted and identified pre-earthquake thermal infrared anomalies for the April 16, 2013 M_W7.8 of Khash, Iran Earthquake. Spatial evolution of anomalies showed the distribution and process. The anomalies were mainly distributed in the east of Khash,Iran.The characteristics of process and distribution presented X-Type model of NE and near NS strip which relates to the geological structure of this region. The epicenter was located near the intersection region of the X-Type abnormal migration process. Besides, the results of time series of anomalies showed that, the duration was more than 40 days and the maximum amplitude was about 18 times. The earthquake occurred 20 days after the abnormal maximum amplitude which appeared on March 26, 2013.     

华北地区中强震前卫星红外亮温变化研究

应用相对功率谱估计方法对华北地区中强地震前静止气象卫星热红外遥感亮温资料进行时频分析, 结果表明: 华北5级以上地震发生前存在显著的亮温热异常, 震前1个月左右异常开始出现, 高值幅值持续时间超过20天, 功率谱幅值最高可以达到平均值的7倍以上, 且发震区域一般位于异常区边缘或异常区域内的断层上。     

一种新型重力测量卫星系统确定全球重力场的性能分析

本文设计了一种高-低卫星跟踪卫星、低-低卫星跟踪卫星和卫星重力梯度测量相结合的新型重力测量卫星系统,其可在一定程度上发挥卫星重力梯度和低低卫星跟踪卫星两种测量模式各自的优势.基于重力卫星系统指标设计的半解析法,深入分析了不同重力测量卫星系统配置和不同观测量及其不同白噪声水平情况下,新型卫星重力测量模式反演重力场模型的能力.数值模拟分析结果表明：在观测值精度和星间距离相同的条件下,轨道高度是影响重力场反演精度的关键因素;随着星间距离的增大,高频重力场信号反演精度会先提高后降低,轨道高度在200~350 km之间时,星间距离在150~180 km之间时反演精度最优;星间距离变率和卫星重力梯度两类观测值仅在某些精度配置时可达到优势互补,如果某一类观测值精度很高,则另一类观测值在联合解算时贡献非常小或者没有贡献.在300 km轨道高度,若以GRACE和GOCE任务的设计指标1 μm·s^-1/√Hz和5 mE/√Hz来配置新型重力测量卫星系统中星间距离变率和引力梯度观测值的精度,联合两类观测值解算200阶次模型大地水准面的精度比独立解算分别提高1.2倍和2.8倍.如果以实现100 km空间分辨率1~2 cm精度大地水准面为科学目标,考虑卫星在轨寿命,建议轨道高度选择300 km,星间距离变率和卫星重力梯度的精度分别为0.1 μm·s^-1/√Hz和1 mE/√Hz.本文的研究成果可为中国研制自主的重力测量卫星系统提供参考依据.     

ZH-1卫星观测的VLF人工源信号特征分析与全波模拟

中国地震电磁监测试验卫星张衡一号(ZH-1)已于2018年2月2日成功发射,正在开展卫星数据在轨测试,并对卫星数据质量进行判定.本文对ZH-1卫星2018年5月至6月夜侧的VLF频段电场功率谱数据进行了分析.通过分析位于不同L值、具有不同发射频率的多个VLF人工源上空的卫星重访轨道观测数据,发现ZH-1卫星记录的人工源信号电场变化标准差与DEMETER卫星记录电场变化标准差几乎一致,说明ZH-1卫星观测数据具有较好的稳定性.通过重访轨道均值与全波模型计算结果对比,发现两者在数值上较为接近,在形态上较为一致,说明ZH-1卫星VLF频段电场功率谱数据具有一定的可靠性.此外,研究了VLF人工源上空及共轭区的电场分布特征和电波传播规律,并与DEMETER卫星的结果进行了对比,结果表明VLF人工源产生的电磁辐射穿透电离层后以导管或者非导管的哨声波模向共轭区传播,因为传播过程中的朗道阻尼,共轭区的电场能量比辐射源顶空更小.VLF人工源位于L1.5时,电磁波传播更容易发生非导管传播,VLF人工源信号导管传播模式在共轭区的电场响应相对于共轭点会发生一定程度北向偏移.     

Spatio-temporal modeling of PM2.5 concentrations with missing data problem: a case study in Beijing,China

ABSTRACT

One of the major challenges in conducting epidemiological studies of air pollution and health is the difficulty of estimating the degree of exposure accurately. Fine particulate matter (PM_2.5) concentrations vary in space and time, which are difficult to estimate in rural, suburban and smaller urban areas due to the sparsity of the ground monitoring network. Satellite retrieved aerosol optical depth (AOD) has been increasingly used as a proxy of ground PM_2.5 observations, although it suffers from non-trivial missing data problems. To address these issues, we developed a multi-stage statistical model in which daily PM_2.5 concentrations can be obtained with complete spatial coverage. The model consists of three stages – an inverse probability weighting scheme to correct non-random missing patterns of AOD values, a spatio-temporal linear mixed effect model to account for the spatially and temporally varying PM_2.5-AOD relationships, and a gap-filling model based on the integrated nested Laplace approximation-stochastic partial differential equations (INLA-SPDE). Good model performance was achieved from out-of-sample validation as shown in R² of 0.93 and root mean square error of 9.64 μg/m³. The results indicated that the multi-stage PM_2.5 prediction model proposed in the present study yielded highly accurate predictions, while gaining computational efficiency from the INLA-SPDE.