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991.
The two-dimensional (2D) autofocus algorithm simultaneously compensates both the residual range migration and propagation-induced phase errors. However, the unsuitable selection of prominent points would reduce the performance of autofocus. Bi-dimensional empirical mode decomposition (BEMD) can decompose a synthetic aperture radar (SAR) image into some different sub-images corresponding to different frequency components. Using proposed 2D autofocus algorithm along with BEMD would help us in selecting the suitable prominent points and give a considerable improvement in the performance of SAR autofocus. In further support of that conclusion, some simulations using real SAR data are demonstrated. 相似文献
992.
993.
The eddy covariance technique has emerged as an important tool to directly measure carbon dioxide, water vapor and heat fluxes between the terrestrial ecosystem and the atmosphere after a long history of fundamental research and technological developments. With the realization of regional networks of flux measurements in North American, European, Asia, Brazil, Australia and Africa, a global-scale network of micrometeorological flux measurement (FLUXNET) was established in 1998. FLUXNET has made great progresses in investigating the environmental mechanisms controlling carbon and water cycles, quantifying spatial-temporal patterns of carbon budget and seeking the “missing carbon sink” in global terrestrial ecosystems in the past ten years. The global-scale flux measurement also built a platform for international communication in the fields of resource, ecology and environment sciences. With the continuous development of flux research, FLUXNET will introduce and explore new techniques to extend the application fields of flux measurement and to answer questions in the fields of bio-geography, eco-hydrology, meteorology, climate change, remote sensing and modeling with eddy covariance flux data. As an important part of FLUXNET, ChinaFLUX has made significant progresses in the past three years on the methodology and technique of eddy covariance flux measurement, on the responses of CO2 and H2O exchange between the terrestrial ecosystem and the atmosphere to environmental change, and on flux modeling development. Results showed that the major forests on the North-South Transect of Eastern China (NSTEC) were all carbon sinks during 2003 to 2005, and the alpine meadows on the Tibet Plateau were also small carbon sinks. However, the reserved natural grassland, Leymus chinensis steppe in Inner Mongolia, was a carbon source. On a regional scale, temperature and precipitation are the primary climatic factors that determined the carbon balance in major terrestrial ecosystems in China. Finally, the current research emphasis and future directions of ChinaFLUX were presented. By combining flux network and terrestrial transect, ChinaFLUX will develop integrated research with multi-scale, multi-process, multi-subject observations, placing emphasis on the mechanism and coupling relationships between water, carbon and nitrogen cycles in terrestrial ecosystems. 相似文献
994.
安徽省会经济圈碳排放强度与生态补偿研究 总被引:2,自引:0,他引:2
通过对1997年和2007年碳排放强度分析,揭示安徽省会经济圈内各市县对碳排放的影响和区域差异,根据相关固碳价格计算省会经济圈市县的生态补偿标准。研究结果显示:(1)省会经济圈总体上为碳汇区,1997—2007年间碳排放总量增加1 049.9万t,年均增长14.4%,其中,合肥市碳排放量增长最大。(2)2007年经济圈内地均建设用地碳排放强度和地均碳排放强度分别增加为1997年的2.18,2.41倍。1997—2007年,省会经济圈内的碳排放量、地均碳排放强度和地均建设用地碳排放都呈现合肥市>巢湖市>六安市。(3)经济圈内各县市地均碳排放强度差异显著,建设用地平均碳排放强度以合肥市最高(784 t/hm2),其次是霍山县和金寨县,其他区域的建设用地平均碳排放强度相差不大。(4)2007年合肥市提供的生态补偿标准是12.8~105.1亿元,六安市和巢湖市得到的生态补偿标准范围分别为31.9~278.1,0.6~13.8亿元;各县市生态补偿差异也很大。 相似文献
995.
For the inversion of ionospheric occultation data, the Abel inversion method of calibrated TEC is usually adopted, but the spherical asymmetry of the real ionosphere will bring errors to the inversion result of electron densities. This paper studies a TEC compensated inversion method. By combining with a background field, this method may eliminate the effect of the horizontal variability of electron density on the TEC, and improve the applicability of the assumption of spherical symmetry as well as the inversion accuracy. Applying this method to the inversion of simulative occultation events, the result demonstrates that compared with the traditional Abel transform inversion, the TEC compensated inversion method can reduce the inversion error. Comparing the various background fields obtained in different ways, it is shown that the higher the coincidence level between the background field and the real field, the better the inversion result. 相似文献
996.
Ximei Hou Guoshun Zhuang Yanfen Lin Juan Li Yilun Jiang Joshua S. Fu 《Journal of Atmospheric Chemistry》2008,61(2):119-131
The indoor PM2.5 aerosol samples for charcoal broiling source under Chinese traditional charbroiling and the ambient fine aerosols samples
(PM2.5) were collected in Beijing to investigate the characteristics of the charcoal broiling source and its impact on the fine
organic aerosols in the atmosphere. The concentrations of 20 species of the trace organic compounds, including polycyclic
aromatic hydrocarbons (PAHs), fatty acids, levoglucosan, and cholesterol in PM2.5 were identified and quantified by GC/MS. The total PAHs and fatty acids emitted from charcoal broiling to PM2.5 were 8.97 and 87,000 ng mg−1 respectively. The concentrations of the light molecular weight (LMW) 3- and 4-ring PAHs were much higher than those of the
high molecular weight (HMW) 5- and 6-ring PAHs. Fatty acids were the most abundant species in source profile, accounting for
over 90% of all identified organic compounds. More polyunsaturated fatty acid (linoleic acids) than the saturated fatty acid
(stearic acids) emitted in the cooking. Charcoal broiling is a minor source of PAHs compared to the source of biomass burning.
Comparing the ratios of levoglucosan/fatty acid and levoglucosan/cholesterol in the charcoal broiling samples to the ambient
samples, it is evident that meat cooking is an important source of fatty acids, but a less important source of cholesterol.
Cooking, as one of the source of fine organic particles, plus other anthropogenic sources would be related to the formation
of the severe haze occurred and spread over the urban atmosphere in most of the cities of China in the past several years. 相似文献
997.
掩星接收机误差对大气温度反演精度影响仿真研究 总被引:1,自引:0,他引:1
为了评估掩星接收机误差对无线电掩星探测精度的影响,利用EGOPS软件仿真研究了多普勒偏差、多普勒频移、时钟稳定性/单差分、接收机噪声和局部多路径等对GNSS无线电掩星反演大气温度、折射率、密度、压力廓线的影响.模拟设计过程中选择METOP作为接收的LEO卫星,GPS星座作为发射系统,设置GRAS天线.从模拟的567个掩星事件中选择了一个上升掩星事件和一个下降掩星事件进行模拟分析.研究结果表明:对于设置的"最差"情况,温度误差最大值大部分出现在平流层顶附近,其中多普勒偏差引起的温度误差最大值接近2 K,多普勒频移引起的温度误差最大值小于0.3 K,时钟稳定性/单差分引起的温度误差最大值接近3 K,现实接收机噪声引起的温度误差最大值超过了4 K,局部多路径引起的温度误差最大值小于1.5 K.经讨论分析认为:对于高质量的无线电掩星反演,掩星接收机误差源中最主要的是接收机热噪声、时钟稳定性/单差分和多普勒偏差.文中还随机选取了30个掩星事件进行统计分析,将其温度反演结果与ECMWF分析场数据比较得出,温度误差的平均偏差在45 km高度上最大,约为1 K;最大标准偏差出现在平流层顶,约为5 K,这验证了廓线反演算法的有效性,表明了误差分析结果的正确性和普遍性. 相似文献
998.
2008年低温雨雪天气扰动能量的积累和传播 总被引:5,自引:1,他引:4
利用NCEP/NCAR再分析资料,通过波包传播的诊断方法,对2008年1月我国南方地区大范围低温雨雪天气期间波包传播和积累进行了分析与研究.分析表明,中低层500hPa和700hPa高度场的波包传播特征能够较好地反映期间出现的4次低温雨雪天气过程.4次雨雪过程基本上产生于波包扰动能量积累的高值时段或处于低压系统持续稳定阶段,雨雪天气处于波包大值区控制下.波包值的经向和纬向传播特征表明2008年1月我国南方地区持续低温雨雪天气过程,主要受到青藏高原南缘系统异常活跃的影响,南支槽活动频繁有利于来自印度洋和孟加拉湾的暖湿气流沿云贵高原不断向我国输送,继而为我国长江中下游以及其南部地区低温雨雪天气提供了充足的水汽来源.偏北路径的冷空气,副高西南侧偏东气流的扰动能量的传播和积累,在波包传播图上都有一定的反映.该研究对进一步利用波包传播图预报天气过程提供了有意义的一种思路. 相似文献
999.
1000.