Apparent and real bias in numerical transfer functions in palaeolimnology

We present an evaluation of the procedure by which model prediction bias is examined in palaeolimnological transfer function inference models. We argue that most of the prediction biases commonly reported in the literature are, in fact, fallacious, and are the artificial consequence of the inappropriate manner in which residuals are traditionally examined. We show that the extent of the specious model bias is entirely predictable from first principles and is essentially determined by the strength of the predictive model. We suggest that the analysis of residuals should always be examined as a function of the model's predictions and we discuss the implications of the old and new approaches.     

金属套管井中电磁测井响应的数值计算

分析了金属套管井中有限尺寸线圈的电磁响应特征,讨论了井眼泥浆参数、套管参数和不同线圈尺寸对电磁测井响应的影响,考察了金属套管中电磁测井对地层电阻率变化的灵敏度.径向非均匀介质的模拟计算表明,在套管井中井眼泥浆对电磁测井的影响较大,必须进行校正.在低频条件下,井间测量响应中金属套管与地层的电磁响应是非耦合的,两者可以分离.在套管参数一定时,套管响应与地层的响应的比值近似一个常数.电磁响应对地层电阻变化的灵敏度分析显示,井间电磁测量在储层研究尺度对地层电阻率变化响应灵敏,套管引起的衰减稳定.在其它参数相同的前提下,线圈直径的增大有助于有效电磁响应信号的增强,给大井间距测量提供了可能.不同磁导率金属套管的电磁响应分析表明,电磁测井中,采用非磁性或弱磁性套管要优于一般的铁磁性套管.     

大地电磁响应函数估算中改进的多道相关函数法及误差的综合评价

近年来,有关大地电磁响应函数估算中消除偏离误差、减少随机误差、评价结果质量方面已有许多研究。Lienert等（1980）提出的多道相关函数法以下式为基础:     

Integer estimation in the presence of biases

 Carrier phase ambiguity resolution is the key to fast and high-precision GNSS (Global Navigation Satellite System) kinematic positioning. Critical in the application of ambiguity resolution is the quality of the computed integer ambiguities. Unsuccessful ambiguity resolution, when passed unnoticed, will too often lead to unacceptable errors in the positioning results. Very high success rates are therefore required for ambiguity resolution to be reliable. Biases which are unaccounted for will lower the success rate and thus increase the chance of unsuccessful ambiguity resolution. The performance of integer ambiguity estimation in the presence of such biases is studied. Particular attention is given to integer rounding, integer bootstrapping and integer least squares. Lower and upper bounds, as well as an exact and easy-to-compute formula for the bias-affected success rate, are presented. These results will enable the evaluation of the bias robustness of ambiguity resolution. Received: 28 September 2000 / Accepted: 29 March 2001     

Remotely sensed estimation of forest canopy density: A comparison of the performance of four methods

In recent years, a number of alternative methods have been proposed to predict forest canopy density from remotely sensed data. To date, however, it remains difficult to decide which method to use, since their relative performance has never been evaluated. In this study the performance of: (1) an artificial neural network, (2) a multiple linear regression, (3) the forest canopy density mapper and (4) a maximum likelihood classification method was compared for prediction of forest canopy density using a Landsat ETM+ image. Comparison of confusion matrices revealed that the regression model performed significantly worse than the three other methods. These results were based on a z-test for comparison of weighted kappa statistics, which is an appropriate statistic for analysis of ranked categories. About 89% of the variance of the observed canopy density was explained by the artificial neural networks, which outperformed the other three methods in this respect. Moreover, the artificial neural networks gave an unbiased prediction, while other methods systematically under or over predicted forest canopy density. The choice of biased method could have a high impact on canopy density inventories.     

提高地磁绝对观测数据精度的有效途径

经过长期观察发现用CZM-2型核旋仪(及其同类仪器)进行定点观测读数时,运用分量仪线圈“单向”旋转的方法进行分量观测,再加上做好一些其它辅助措施,能够充分消除人为因素和仪器本身误差所带来的影响,明显提高仪器的观测精度,达到使观测资料更加准确的目的。     

A source of bias in rates of surface soil movement as estimated from marked particles

When estimated from measurements of introduced tracer particles, the rate of surface soil movement tends to be greater than the natural rate for equivalent particles on the same site. This consistent overestimation is greatest in the period following tracer introduction and leads to a measurement bias that may be as high as 300 per cent. The magnitude of the bias decreases with time, as the tracer is incorporated into the surface material, but remains detectable statistically for more than a year on some low-angle sites.     

基于遗传算法的瞬变电磁法线圈阵列优化设计

为解决瞬变电磁检测技术遇到地底干扰物时在探测精度方面的不足,从载流直导线出发,利用磁场矢量叠加原理,计算单个正三角形空间磁场分布,设计了一种正三角形发射线圈阵列。为得到更好的磁聚焦特性,利用遗传算法对线圈阵列的具体参数进行优化。仿真结果表明:87.5%及以上的磁场能量集中在半径0.113m的特定区域内。说明该线圈阵列在较小目标区域实现了聚焦,具有良好的聚焦性,可以应用在瞬变电磁检测技术发射回线中。     

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地埋管地源热泵技术在贵州岩溶地区的应用研究

地埋管热泵技术是采集地表以下200 m深度内的浅层地热能进行供热制冷的新型能源利用技术,而该技术在贵州碳酸盐岩分布区的应用和推广之所以受到制约,其主要原因是岩溶地层中建造垂直换热孔的难度大、成本较高。通过贵州省有色科技大楼附楼采用垂直地埋管式与基础桩螺旋盘管式有效组合的换热系统,在岩溶一般至中等发育的碳酸盐岩地层中开发利用浅层地热能的成功经验的介绍,为地埋管热泵技术在贵州岩溶地区的应用和推广提供参考。