The Matérn variogram model: Implications for uncertainty propagation and sampling in geostatistical surveys

The Matérn variogram model has been advocated because it is flexible and can represent varied behaviour at small lags. We show how the constraints on the spherical and exponential variogram at short lags ignore a possible source of uncertainty in the variogram and so in kriging surveys, that the Matérn model can describe. Matérn, spherical and exponential variogram models were fitted by maximum likelihood to a set of log₁₀(K) observations made on a regular grid at Broom's Barn Farm, Suffolk, England. The likelihood profiles of the Matérn parameter estimates were asymmetric. Thus the uncertainty of these estimates could only be adequately assessed by a Bayesian approach. The uncertainty of estimated parameters of the Matérn variogram was larger than for the exponential variogram. This is an indication that the assumption of an exponential model limits the behaviour that may be described by the variogram. Thus uncertainty analyses where an exponential variogram is assumed may underestimate the uncertainty of kriged estimates. Bayesian analysis of the kriged estimates of log₁₀(K) at Broom's Barn Farm using the Matérn variogram revealed an observable component of uncertainty due to variogram uncertainty. When an exponential variogram model was used, the estimate of this component of uncertainty was negligible. The Matérn variogram should therefore be used rather than the exponential model when assessing the adequacy of a variogram estimate. A method of designing sample schemes which is suitable for both estimating a Matérn variogram and interpolation is suggested.     

鱼和虾中组胺残留量HPLC法测定的不确定度评定

利用高效液相色谱法对组胺残留量的检测,建立鱼和虾中组胺残留量的不确定度分析方法,进而对鱼虾中组胺的残留量不确定度进行分析评定。结果表明,HPLC法测定添加水平50 mg/kg的组胺残留量的结果可表示为:X=(48.97±3.98)mg/kg,包含因子k=2。     

液相色谱-串联质谱法测定猪肉中四环素类药物残留量的不确定度评定

评定液相色谱-串联质谱法（LC-MS/MS）测定猪肉中四环素类药物残留量的不确定度。依据GB/T 21317-2007《动物源性食品中四环素类兽药残留量检测方法 液相色谱-质谱/质谱法与高效液相色谱法》,建立相关数学模型,对实验过程中的不确定度来源进行分析与评定。当采用LC-MS/MS法测定猪肉中土霉素、四环素、金霉素、强力霉素的残留量分别为50.05、42.81、42.45、41.60μg/kg时,扩展不确定度分别为 5.44、6.72、2.86、4.80μg/kg (k=2)。检测结果的不确定度主要受回收率、标准溶液配制、工作曲线拟合的影响。     

Evaluation method dependency of measured saturated hydraulic conductivity

Saturated hydraulic conductivity (Ks) is one of the most important hydraulic properties affecting water flow in soils. Spatial and seasonal variability as well as scale dependency are key factors which make it more difficult to accurately measure the saturated hydraulic conductivity. The uncertainty of the Ks values due to different evaluation methods was investigated using raw measured data obtained on two different Hungarian soils with three different in situ measuring devices (double ring, tension disc and mini disc infiltrometers), as well as with two laboratory methods. Since the very same raw infiltration data could result in significantly different Ks values, we have introduced the evaluation method dependency of the measured Ks values. Our investigations found that the effect of the applied evaluation method for assessing raw measured data can be just as significant as the effect of other factors, such as the scale effect, as well as the spatial and temporal variability.     

小麦水分含量测量不确定度的分析评定

[目的]分析评定小麦水分含量的测量不确定度.[方法]分析了测定小麦水分含量测量不确定度的来源,采用GB 5009.3-2010标准方法测定小麦水分含量,并对测量不确定度的影响因素进行分析.[结果]通过分析评定测定结果的不确定度,得出小麦水分含量测定结果扩展不确定度为0.03％.[结论]在小麦水分含量测量不确定度评定时,重复测量小麦水分含量是影响其测量不确定度的主要因素.     

HPLC荧光检测鱼肉中孔雀石绿残留量的不确定度

通过数学建模,对GB/T20361-2006 HPLC法荧光检测鱼肉中孔雀石绿残留量的不确定度进行分析。结果表明,合成标准不确定度U(X)=0.048,测量鱼肉中孔雀石绿残留量的不确定度为(2.00±0.19)μg/kg。     

基于样点个体代表性的大尺度土壤属性制图方法

大空间尺度范围的土壤属性分布信息是陆地表层过程模拟的基础信息.基于野外样点进行空间插值是获得土壤属性空间分布信息的重要手段.现有的空间插值方法通常要求所用样点对研究区土壤属性空间分布规律具有良好的全局代表性.然而,受采样经费和野外采样条件的限制,所采集的样点往往难以全面地反映研究区土壤属性的空间分布规律.基于这样的样点用现有空间插值方法得到的土壤属性分布图通常精度较低,并且由样点全局代表性差带来的推测不确定性也无法得到度量.为了合理利用这些已采集的但全局代表性不好的样点,本文提出了基于样点“个体代表性”推测土壤属性空间分布并度量推测不确定性的方法.该方法在两点环境条件越相似、土壤属性就越相似的假设下,认为每一样点可以代表与其环境条件相似的地区,并且代表程度可以由两点的环境相似度度量;通过分析环境相似度计算推测不确定性,并以环境相似度为权重计算样点可代表地区的土壤属性值.将该方法应用于推测新疆伊犁地区土壤表层有机质含量,经验证,本文方法能够有效地利用全局代表性差的样点推测样点能够代表地区的土壤属性空间分布,并且所得的推测不确定性与预测残差呈现正向关系,能够有效地指示推测结果的可靠程度.     

饲料中铜的测量不确定度评定

对原子吸收光谱法测定饲料中铜不确定度进行评定。对影响测量结果的重复性、标准溶液、溶液体积、检测仪器等主要因素引起的不确定度进行了逐个分析评定,并进行了整体合成。评定过程清晰合理,主要影响因素不遗漏、不重复,适用于原子吸收光谱法的测量不确定度评定。     

土壤重金属污染风险预测研究进展

对土壤重金属污染评价及预测的3种主要技术理论进行了阐述,评述了3种技术理论的优缺点,并进一步分析了土壤重金属污染风险预测不确定性的研究方法及影响因素。     

Risk Perception Among Non-industrial Private Forest Owners

Based on an enquiry, risk perception among non-industrial private forest owners is described in relation to climate change and forestry hazards. Of the respondents, 11% took action to remedy the effects of climate change. Out of a given set, hazards were ranked according to each respondent's experience of recent substantial financial loss to the estate and in relation to his or her willingness to make investments aimed at risk reduction. For each hazard, the respondent assessed the risk in four classes ranging from very high to negligible risk. Six hazards were considered most problematic in all three aspects: browsing damage, falling timber prices, damage by wind, spruce bark beetle, root rot and pine weevil. A majority of the respondents claimed to take action to reduce the risk associated with at least one hazard, while 35% did not know whether they did. Excluding climate change, the need for decision support was the largest in relation to damage by wind owing to a combination of perceived high risk and a high level of ignorance in relation to whether risk-reducing measures were taken.