Watershed scale temporal and spatial stability of soil moisture and its role in validating satellite estimates

Watershed scale soil moisture estimates are necessary to validate current remote sensing products, such as those from the Advanced Microwave Scanning Radiometer (AMSR). Unfortunately, remote sensing technology does not currently resolve the land surface at a scale that is easily observed with ground measurements. One approach to validation is to use existing soil moisture measurement networks and scale these point observations up to the resolution of remote sensing footprints. As part of the Soil Moisture Experiment 2002 (SMEX02), one such soil moisture gaging system in the Walnut Creek Watershed, Iowa, provided robust estimates of the soil moisture average for a watershed throughout the summer of 2002. Twelve in situ soil moisture probes were installed across the watershed. These probes recorded soil moisture at a depth of 5 cm from June 29, 2002 to August 19, 2002. The sampling sites were analyzed for temporal and spatial stability by several measures including mean relative difference, Spearman rank, and correlation coefficient analysis. Representative point measurements were used to estimate the watershed scale (∼25 km) soil moisture average and shown to be accurate indicators with low variance and bias of the watershed scale soil moisture distribution. This work establishes the validity of this approach to provide watershed scale soil moisture estimates in this study region for the purposes of satellite validation with estimation errors as small as 3%. Also, the potential sources of error in this type of analysis are explored. This study is a first step in the implementation of large-scale soil moisture validation using existing networks such as the Soil Climate Analysis Network (SCAN) and several Agricultural Research Service watersheds as a basis for calibrating satellite soil moisture products, for networks design, and designing field experiments.     

一种基于0.18-μm CMOS工艺的新型超宽频带毫米波混频器设计与分析

本文提出了一种超宽频带毫米波混频器电路.混频器采用分布式拓扑结构和中频功率合成技术,具有宽带宽和高转换增益.该混频器采用TSMC 0.18-μm CMOS工艺设计并制造,芯片总面积为1.67mm².测试结果表明:混频器工作频率从8GHz到40GHz,中频频率为2.5GHz时的转换增益为-0.2dB至4dB,其本振到中频端口和射频到中频端口间的隔离度均大于50dB.整个电路的直流功耗小于32mW.     

毫米波/红外复合导引头关键技术分析

文中分析了毫米波/红外双模复合制导技术的特点,介绍了国外发展的情况,并对毫米波/红外复合导引头的关键技术进行了详细的分析.     

毫米波频率综合技术研究

本文阐述了Ｋａ波段频率综合器的研究方案及实现方法,主要包括毫米波主环、微波参考环和中频锁相环的构成,以及用此方法设计实现的输出频率为２６．５￣４０ＧＨｚ,频率间隔１ＭＨｚ,相位噪声指数￡（１０ｋＨｚ）〈－６５ｄＢｃ／Ｈｚ,杂散优于－５５ｄＢｃ,输出功率大于＋５ｄＢｍ的毫米波频率综合器。论文同时研究了毫米波频率综合顺中所需的微波参考源,其频率范围为２．６１￣３．９６ＧＨｚ,相位噪声指标￡（１０ｋＨｚ     

一种基于毫米波/红外复合制导的跟踪滤波算法

信息融合技术是毫米波/红外复合制导的关键技术之一,其中目标跟踪算法的优劣直接决定了系统的性能.针对毫米波与红外复合制导的目标跟踪,首先对毫米波传感器和红外传感器的量测数据进行了融合,并提出了一种改进的跟踪滤波算法.该跟踪算法能根据目标的机动情况实时获得滤波增益,并及时调整滤波方程,从而获得良好的跟踪效果.最后对目标的直线运动和改变航向的直线运动进行了仿真分析.仿真结果表明,与其它滤波算法相比,该算法的跟踪效果良好,跟踪精度较高且计算量少.     

被动毫米波制导下辐射特性控制的考虑

为提高地面目标在未来战场的生存能力,分析了被动毫米波探测与制导的作用原理与实际威胁,指出了目标的毫米波辐射特性控制的实际需要。在对毫米波辐射特性测量机理的深入分析,与辐射计探测距离公式的推导、讨论基础上,指出毫米波辐射特性控制的主要方向为目标的形状和材料特性的控制,并从这两方面分析了辐射特性控制的实际措施。     

Development of a daily long term record of NOAA-14 AVHRR land surface temperature over Africa

We developed a new 6-year daily, daytime and nighttime, NOAA-14 AVHRR based land surface temperature (LST) dataset over continental Africa for the period 1995 through 2000. The processing chain was developed within the Global Inventory Modeling and Mapping System (GIMMS) at NASA's Goddard Space Flight Center. This paper describes the processing methodology used to convert the Global Area Coverage Level-1b data into LST and collateral data layers, such as sun and view geometries, cloud mask, local time of observation, and latitude and longitude. We used the Ulivieri et al. [Ulivieri, C., M.M. Castronuovo, R. Francioni, and A. Cardillo (1994), A split window algorithm for estimating land surface temperature from satellites, Adv. Space Research, 14(3):59-65.] split window algorithm to determine LST values. This algorithm requires as input values of surface emissivity in AVHRR channels 4 and 5. Thus, we developed continental maps of emissivity using an ensemble approach that combines laboratory emissivity spectra, MODIS-derived maps of herbaceous and woody fractional cover, and the UNESCO FAO soil map. A preliminary evaluation of the resulting LST product over a savanna woodland in South Africa showed a bias of < 0.3 K and an uncertainty of < 1.3 K for daytime retrievals (< 2.5 K for night). More extensive validation is required before statistically significant uncertainties can be determined. The LST production chain described here could be adapted for any wide field of view sensor (e.g., MODIS, VIIRS), and the LST product may be suitable for monitoring spatial and temporal temperature trends, or as input to many process models (e.g., hydrological, ecosystem).     

Eigen-Range Profiles for Radar Target Classification

Ｅｉｇｅｎ－ＲａｎｇｅＰｒｏｆｉｌｅｓｆｏｒＲａｄａｒＴａｒｇｅｔＣｌａｓｓｉｆｉｃａｔｉｏｎＪＩＡＮＧＹｉｃｈｅｎｇ；ＷＡＮＧＪｉｎｒｏｎｇ（姜义成）；（王金荣）（ＤｅｐｔｏｆＣｏｍｍｕｎｉｃａｔｉｏｎａｎｄＥｌｅｃｔｒｏｎｉｃＥｎｇｉｎｅｅｒｉｎ...     

毫米波辐射计缩比测试研究

缩比测试是在较低高度下对满足缩比条件的小目标进行测试,以等效在真实高度下对大目标进行测试的情况。文中针对毫米波辐射计的探测研究,讨论了其缩比测试的原理及条件,并在两种高度下进行了实际的毫米波辐射计缩比测试及相应真实高度下的塔载测试,结果对比表明了缩比测试的可信性。该方法简单易行,可节省大量经费。     

空地导弹雷达导引头最新技术进展

本文总结了国外空地导弹雷达导引头最新进展,对当前空地导弹雷达导引头研制中存在的关键技术进行了分析,认为常规毫米波雷达导引头由于受方位分辨率限制很难彻底解决目标自动分类问题,毫米波雷达与红外成像或SAR成像复合制导技术可以从根本上解决目标自动分类问题,必将在未来精确制导领域发挥重要作用。