FY-4A AGRI辐射率资料偏差特征分析及订正试验     

耿晓雯  闵锦忠  杨春  王元兵  许冬梅 《大气科学》2020,44(4):679-694

风云四号A星（Fengyun-4A,简称FY-4A）作为我国最新一代静止气象卫星,各方面技术指标都体现了“高、精、尖”特色,处于国际领先地位。其上搭载的多通道扫描成像辐射计（Advanced Geosynchronous Radiation Imager,简称AGRI）较上一代静止卫星风云二号的可见光红外自旋扫描辐射仪观测精度更高、扫描时间更短,充分体现AGRI观测资料将有效提高“一带一路”沿线国家和地区的天气预报和灾害预警水平。偏差订正是卫星资料处理的重要环节之一,因此本文通过在WRFDA v3.9.1（Weather Research and Forecasting model’s Data Assimilation v3.9.1）搭建AGRI同化接口,利用RTTOV v11. 3辐射传输模式和GFS全球预报系统（Global Forecast System）分析场研究了FY-4A AGRI红外通道8～14晴空辐射率资料的偏差特征并进行偏差订正对比试验,分析了卫星天顶角对AGRI资料偏差订正的影响,为将来实现AGRI红外通道辐射率资料在中尺度模式中的同化应用奠定基础。结果表明:（1）通道8～10及14为正偏差,通道11～13为负偏差。水汽通道9和10偏差及其标准差相对较小,偏差海陆差异不明显。通道11～14探测高度较低,陆地上观测受地表发射率影响大,质量控制时可剔除这些通道陆地上的观测。（2）各通道偏差随卫星天顶角变化的拟合直线斜率都小于0.035,对比试验结果表明偏差与卫星天顶角的关系不明显,预报因子中无需考虑卫星天顶角的作用。（3）通道8及11～14的偏差随着目标亮温的变化比水汽通道9～10明显,偏差有较强的目标亮温依赖特征。（4）根据分析的偏差特征对2018年5月13日18时（协调世界时,下同）至15日18时进行变分偏差订正试验,系统性偏差得到了有效的订正。  相似文献   

Bias aware Kalman filters: Comparison and improvements   总被引：1，自引：0，他引：1  

Jean-Philippe Drécourt  Henrik Madsen  Dan Rosbjerg 《Advances in water resources》2006

This paper reviews two different approaches that have been proposed to tackle the problems of model bias with the Kalman filter: the use of a colored noise model and the implementation of a separate bias filter. Both filters are implemented with and without feedback of the bias into the model state. The colored noise filter formulation is extended to correct both time correlated and uncorrelated model error components. A more stable version of the separate filter without feedback is presented. The filters are implemented in an ensemble framework using Latin hypercube sampling. The techniques are illustrated on a simple one-dimensional groundwater problem. The results show that the presented filters outperform the standard Kalman filter and that the implementations with bias feedback work in more general conditions than the implementations without feedback.  相似文献   

Problems of bias in mapping linear landforms from satellite imagery     

《International Journal of Applied Earth Observation and Geoinformation》2007,9(1):65-78

Remotely sensed images are an important data source for the mapping of glacial landforms and the reconstruction of past glacial environments. However the results produced can differ depending on a wide range of factors related to the type of sensors used and the characteristics of the landforms being mapped. This paper uses a range of satellite imagery to explore the three main sources of variation in the mapped results: relative size, azimuth biasing and landform signal strength. Recommendations include the use of imagery illuminated with low solar elevation, although an awareness of the selective bias introduced by solar azimuth is necessary. Landsat ETM+ imagery meets the requirements for glacial landform mapping and is the recommended data source. However users may well have to consider alternative data in the form of SPOT, Landsat TM or Landsat MSS images. Digital elevation models should also be considered a valuable data source.  相似文献   

FHD仪偏置线圈电流反向对D分量基线值的影响及修正方法     

高登平  李细顺  胡秀娟  解用明  王利兵  杨锐 《山西地震》2007,(3):34-36

在地磁连续观测中,需要通过分析计算观测数据对仪器的工作状态作出正确的判断,介绍了判断FHD仪偏置线圈电流是否反向的2种方法,研究了反向前后基线值的变化情况并提出了修正方法。  相似文献   

Philips磁共振射频软故障的检修与分析   总被引：1，自引：0，他引：1  

刘宏  刘颖 《CT理论与应用研究》2001,10(3):39-41

Philips T5-NT磁共振设备中的射频放大器出现了偏流超出正常值的软故障,经过测试软件测试,以及进行最大功率调节等处理,最终判定功率放大部件故障,并由替代法证实。  相似文献   

Accuracy and precision of methods for estimating river loads   总被引：1，自引：0，他引：1  

R. I. Ferguson 《地球表面变化过程与地形》1987,12(1):95-104

River loads often have to be estimated from continuous discharge data but relatively infrequent sampling of sediment, solute, or pollutant concentrations. Two standard ways of doing this are to multiply mean concentration by mean discharge, and to use a rating curve to predict unmeasured concentrations. Both methods are known from previous empirical studies to underestimate true load. Statistical considerations explain these biases and yield correction factors which can be used to obtain unbiased estimates of load. Simulation experiments with normally-distributed scatter about log-linear trends, and sampling experiments using a natural data set, show that the corrected rating curve method has lower sampling variability than other unbiased methods based on average instantaneous load and is thus the recommended procedure when the rating plot is of the assumed form. The precision of all methods increases with sample size and decreases with increasing rating-curve slope and scatter.  相似文献   

Exploring the possibilities for star-tracker assisted calibration of the six individual GOCE accelerometers   总被引：1，自引：0，他引：1  

P. N. A. M. Visser 《Journal of Geodesy》2008,82(10):591-600

A method has been developed and tested for estimating calibration parameters for the six accelerometers on board the Gravity field and steady-state Ocean Circulation Explorer (GOCE) from star tracker observations. These six accelerometers are part of the gradiometer, which is the prime instrument on board GOCE. It will be shown that by taking appropriate combinations of observations collected by the accelerometers, by modeling acceleration terms caused by gravity gradients from an a priori low-degree spherical harmonic expansion, and by modeling rotational acceleration terms derived from star-tracker observations, scale factors of each of the accelerometers can be estimated for each axis. Simulated observations from a so-called end-to-end simulator were used to test the method. This end-to-end simulator includes a detailed model of the GOCE satellite, its instruments and instrument errors, and its environment. Results of the tests indicate that scale factors of all six accelerometers can be determined with an accuracy of around 0.01 for all components on a daily basis.  相似文献   

集合模式定量降水预报的统计后处理技术研究综述   总被引：8，自引：0，他引：8  

代刊  朱跃建  毕宝贵 《气象学报》2018,76(4):493-510

集合数值模式预报已在定量降水预报业务中广泛应用,以获得预报不确定性、最可能预报结果以及极端天气预警。由于集合系统的数值模式不完善,且不能提供所有的不确定性信息,常表现出系统性偏差以及欠离散或过离散（如对于多模式集合）。为此,需要发展统计后处理技术,在尽量保持集合预报解析度的条件下,提高预报的技巧和可靠性。近年来,各种集合预报统计后处理技术得到快速发展。针对定量降水预报,依据技术方法的途径和成熟度将后处理研究归纳为3方面进行总结,包括:（1）不基于统计模型的非参数化后处理,包括集合定量降水预报偏差订正、多成员或模式信息集成以及基于空间分析的对流尺度模式后处理;（2）基于概率分布统计模型的参数化后处理,包括集合模式输出统计和贝叶斯模型平均两种方法框架;（3）考虑预报量的时间、空间和多变量间依赖关系或结构的处理方法,包括参数化和经验连接概率法。最后,讨论发展统计后处理技术需要关注的问题,包括考虑不同来源、不同尺度的多模式信息集成;提供高质量、高分辨率的降水分析资料;发展再预报技术扩充训练样本;基于不同的订正目的和应用场景来使用不同的后处理技术;发展面向海量预报数据、捕捉极端降水以及考虑预报量结构的新技术。   相似文献   

四种定量降水预报客观订正方法对比研究   总被引：1，自引：0，他引：1  

苏翔  袁慧玲  朱跃建 《气象学报》2021,79(1):132-149

基于2019年全年、不同季节、不同预报时效的欧洲中期天气预报中心模式的定量降水预报,检验评估了频率匹配、最优TS评分、最优百分位、概率匹配4种定量降水预报客观订正法的综合性能。利用理想模型研究了不同雨带位移偏差和干湿偏差情形下频率匹配法与最优TS评分的表现,并通过个例订正展示了4种定量降水预报订正法的基本特征。结果表明:频率匹配与最优TS评分仅能对确定性预报的降水量级进行调整,最优百分位和概率匹配法通过引入集合预报信息可在一定程度上改变预报的降水落区。频率匹配法以频率偏差最优为目标,可以很好地消除模式的干湿偏差,但仅在位移偏差较小且存在较大干湿偏差时提升原始预报的TS评分。最优TS评分法难以改进存在弱湿偏差的中雨预报的TS评分,而最优百分位法利用集合预报信息可以显著提升所有降水等级的TS评分,在较长预报时效下优势尤其明显,但也存在春、夏两季湿偏差较大的问题。概率匹配法由于没有使用历史实况信息,在暴雨订正中干偏差较大。经济价值模型检验评估表明,最优百分位法在暴雨量级的风险决策中具有较高的参考价值。   相似文献   

基于RegCM4模式的中国区域日尺度降水模拟误差订正   总被引：4，自引：0，他引：4  

童尧  高学杰  韩振宇  徐影 《大气科学》2017,41(6):1156-1166

气候模式模拟得到的各气候变量与观测相比,总会存在一定的偏差,所得到的气候变化预估结果难以在影响评估模型中直接应用。本文尝试对一个区域气候模式（RegCM4.4）所模拟的中国区域逐日降水,基于概率分布（分位数映射）方法进行统计误差订正。在订正过程中,以模拟时段1991~2010年中的前半段（1991~2000年）作为参照时段,建立传递函数,对后一时段（2001~2010年）进行订正并检验其效果。首先对使用参数和非参数所建立的6种不同传递函数方法进行对比,发现6种方法均可明显减少降水模拟的误差,其中利用非参数转换建立传递函数的RQUANT方法效果更好。随后进一步分析了采用该方法对模式模拟降水所做订正的效果,结果表明,该方法可以明显改善对平均降水,以及降水年际变率和极端事件的模拟结果。  相似文献