复杂地形下地面观测资料同化III. 两种解决模式地形与观测站地形高度差异方法的对比分析

模式地形与观测站地形高度差异是地面资料同化方案设计中的一大难点。本文通过个例和单点试验对第I和第II部分 (徐枝芳等, 2007a, 2007b) 中涉及的两种解决模式地形与观测站地形高度差异的地面资料同化方法 (即增加温度地形代表性误差和温度订正方法) 进行对比分析, 并将这两种方法应用于WRF_3DVAR, 进行3个月的连续数值试验。研究结果表明: 随着地形高度差异的增加, 采用增加观测误差方法得到的估计值向其它资料同化分析值 (背景场值) 靠近, 在一定的高度差异下则失去了同化分析地面资料的意义; 温度订正方法对温度递减率的取值较为敏感, 在有探空资料参与同化分析时, 温度递减率取值敏感性相对减弱。当采用的订正值较为准确时, 采用温度订正方法较增加观测误差方法能更好地处理两种地形高度差异, 地面资料信息应用更充分, 得到的估计值最有可能接近真实值。当模式地形与观测站地形高度差异较小 (小于100 m) 时, 两种解决模式地形与观测站地形高度差异的方法达到的效果基本一致。单点及个例试验表明, 有探空资料等高质量观测参与同化分析时, 采用增加观测误差方法得到分析场更接近真实场。三个月连续试验也表明有探空资料参与同化分析时, 采用增加观测误差方法比温度订正法改进的郭永润同化方案 (Guo et al., 2002) 同化地面资料效果好, 且加入地面资料同化对所有量级降水预报都有所改善。当地面资料同化方案没处理好时, 加入地面资料同化的效果反而不如不加地面资料同化。     

NCAR分析资料在大气边界层内误差的初步分析

通过比较1998年南海季风试验(SCSMEX)期间(1998年5月5日～5月25日,6月4日～6月20日)7个站点的探空加密观测资料与NCAR分析资料,分析了在大气边界层内分析资料存在的误差.结果表明:在大气边界层内,NCAR分析资料存在较大的误差.位温和比湿误差随着高度的增加呈现下高上低的特征.比湿的误差要大于位温的误差,7个站点的位温均方差最小值基本都小于1 K,最大均方差也不大于2 K,而比湿均方差最小值基本都大于1.0 g·kg~(-1),部分站点的误差最大值超过2.0 g·kg~(-1).初步说明,下垫面对NCAR分析资料误差的产生有较大影响,内陆地区和海岛地区的分析资料位温的误差比沿海地区大,而比湿数据则相反;在垂直方向上,分析资料的位温误差在0.98～1.33 K之间,比湿误差介于1.39～1.60 g·kg~(-1)之间.     

公路水准测量的误差来源与控制

水准测量是确定公路工程地面点高程的方法之一,是高程测量中精度较高常用方法。实施过程中,需要几个人合作才能完成。误差允许范围内的精度由于仪器和人为的影响而不容易控制,而且易出现隐蔽性错误。如果不能及早发现基础资料是错误的,水准点高程不正确,直接影响路线纵断面设计和施工。本文就水准测量的工作原理、误差来源,误差控制等几方面结合工程实例进行分析。     

Array processing-a new method to detect and correct errors on array resistivity logging tool measurements

In recent years more and more multi-array logging tools, such as the array induction and the array lateralog, are applied in place of conventional logging tools resulting in increased resolution, better radial and vertical sounding capability and other features. Multi-array logging tools acquire several times more individual measurements than conventional logging tools. In addition to new information contained in these data, there is a certain redundancy among the measurements. The sum of the measurements actu- ally composes a large matrix. Providing the measurements are error-free, the elements of this matrix show certain consistencies. Taking advantage of these consistencies, an innovative method is developed to de- tect and correct errors in the array resistivity logging tool raw measurements, and evaluate the quality of the data. The method can be described in several steps. First, data consistency patterns are identified based on the physics of the measurements. Second, the measurements are compared against the consis- tency patterns for error and bad data detection. Third, the erroneous data are eliminated and the measure- ments are re-constructed according to the consistency patterns. Finally, the data quality is evaluated by comparing the raw measurements with the re-constructed measurements. The method can be applied to all array type logging tools, such as array induction tool and array resistivity tool. This paper describes the method and illustrates its application with the High Definition Lateral Log (HDLL, Baker Atlas) instru- ment. To demonstrate the efficiency of the method, several field examples are shown and discussed.     

Earthquake source model using strong motion displacement as response of finite elastic media

The strong motion displacement records available during an earthquake can be treated as the response of the earth as the a structural system to unknown forces acting at unknown locations. Thus, if the part of the earth participating in ground motion is modelled as a known finite elastic medium, one can attempt to model the source location and forces generated during an earthquake as an inverse problem in structural dynamics. Based on this analogy, a simple model for the basic earthquake source is proposed. The unknown source is assumed to be a sequence of impulses acting at locations yet to be found. These unknown impulses and their locations are found using the normal mode expansion along with a minimization of mean square error. The medium is assumed to be finite, elastic, homogeneous, layered and horizontal with a specific set of boundary conditions. Detailed results are obtained for Uttarkashi earthquake. The impulse locations exhibit a linear structure closely associated with the causative fault. The results obtained are shown to be in good agreement with reported values. The proposed engineering model is then used to simulate the acceleration time histories at a few recording stations. The earthquake source in terms of a sequence of impulses acting at different locations is applied on a 2D finite elastic medium and acceleration time histories are found using finite element methods. The synthetic accelerations obtained are in close match with the recorded accelerations.     

T63模式对暴雨短期预报能力的分析检验

利用Ｔ６３模式的５００ｈＰａ数值形势预报图和客观分析实况图，对１９９４年７－９月我国出现的１２次较大范围暴－大暴雨天气过程的影响天气系统进行了预报能力的分析检验，并分析了产生误差的原因，所得结果有利于数值预报产品的释用及实时预报业务。     

气象因素对飞行安全高度的影响

通过分析气象因素对气压式高度表测量高度的影响，求出了高度误差极值，说明了我国安全高度按高于航线两侧２５ｋｍ范围内的最大标高４００ｍ或６００ｍ存在一定误差，提出了４条预防措施。     

“频谱分析法”在兰州市地下水水源地水情预报中的应用

利用“频谱分析法”预报地下水位经实际监测结果的误差检验，认为该方法用于地下水水源地水位预报是基本可行的。为今后广泛开展地下水情预测预报提供了一条有效途径。     

Error analysis of exterior orientation elements on geolocation for a Moon-based Earth observation optical sensor

ABSTRACT

The Moon is a potential new platform for Earth observation. The advantages of its large-scale observational scope, long temporal duration, and multi-layer detecting of the Earth will undoubtedly advance our understanding of the Earth system. To carry out the observations from a Moon-based optical sensor, the geolocation error caused by exterior orientation elements need to be investigated. This paper analyses the error effects of exterior orientation elements on geolocation for an optical sensor. To estimate the error, we present a geometric image model and utilise some parameters to measure the image offsets. Through a large number of numerical simulations, the results demonstrate that the image offsets are not obvious influenced by the distance and observation angle at mid-high latitude of the Moon and have linear correlation with the increasing errors of the exterior orientation elements. Further, the relationship between the spatial resolution and errors of exterior orientation elements are revealed. Finally, the error characteristics for Moon-based Earth observation are discussed. It is expected that the conclusion drawn in this paper could support the study of a Moon-based Earth observation optical sensor.     

TDJ7型精密陀螺经纬仪的系统误差研究

新近研制的国产ＴＤＪ７型陀螺经纬仪，采用永磁直流陀螺马达，计算机采集处理数据技术和光电积分自动测量方法，是一种先进的现代陀螺寻北系统。本文根据试验观测的大量数据，对其因温度效应和应用参数引起的系统误差进行了理论研究，提出了定点步进定间距计算改正、合理确定扭力零位权、优化求解角度当量值和扭力矩系数等措施，从而有效地减小了系统误差，显著提高了仪器的定向精度。