基于空间自相关和概率论的土壤重金属异常值的 识别方法
作者简介:王景云(1990-),男,山东临沂人,硕士生,研究方向为地理环境演化与分析。E-mail:wjy603@126.com
收稿日期: 2016-09-23
要求修回日期: 2016-11-01
网络出版日期: 2017-05-20
基金资助
国家自然基金面上项目“同位素标识蜈蚣草对Pb污染土壤修复的调控机理探索”(41271478)
国家“863”课题“土壤重金属污染现场监测技术与设备”(2014AA06A513)
A Method for Detecting Outliers of Soil Heavy Metal Data Based on Spatial Autocorrelation and Probability Theory
Received date: 2016-09-23
Request revised date: 2016-11-01
Online published: 2017-05-20
Copyright
数据是开展土壤环境质量研究的基础,在实验过程中,由于系统误差和人为误差导致数据异常、降低数据质量,进而对污染评价、修复与管理决策等后续工作带来误判。目前对于此方面缺乏深入的研究和探讨。基于此,本研究提出一种甄别土壤重金属异常数据的方法,并以北京市土壤Cd含量数据为例,对该方法的有效性进行了验证。结果显示,北京市651个土壤Cd数据中有34个数据异常,对甄别出的异常数据进行化学复测,发现76.5%的Cd异常数据(26个)为系统误差和人为误差导致;20.6%的异常数据(7个)为客观存在的异常点。将原始数据修正后,插值预测精度得到了显著提高。Cd异常数据自身的平均相对误差下降44.56%,均方根误差降低33.33%;受异常值影响的邻近点平均相对误差下降20.59%,均方根误差降低17.33%。结果表明本方法可以有效识别出土壤重金属数据中的异常数据,在增加有限样本量和分析时间的前提下提高调查数据质量,为开展区域土壤调查,保障数据质量提供有效的工具。
王景云 , 杨军 , 杨俊兴 , 雷梅 , 万小铭 , 周小勇 , 陈同斌 , 张红日 , 赵相伟 . 基于空间自相关和概率论的土壤重金属异常值的 识别方法[J]. 地球信息科学学报, 2017 , 19(5) : 605 -612 . DOI: 10.3724/SP.J.1047.2017.00605
Data was the basis of carrying out the research on environmental quality of the soil. However, in the experimental process, the systematic errors and artificial errors may lead to some outliers, which may reduce the data quality and cause erroneous judgement for pollution assessment and management decision. At present, there was a lack of thorough study and exploration in this respect. Based on this, a method for detecting outliers of soil heavy metal data was put forward in this study. The soil Cd concentration of Beijing in China was taken as an example to verify the validity of the method. The results show that there are 34 outliers for Cd concentration in Beijing. The detected outliers in Beijing were re-analysed. The results showed that 76.5% of the outliers were found to be caused by the systematic errors and artificial errors and 20.6% of the outliers existed, objectively. After the correction, the interpolation accuracy was improved significantly. The mean relative error and mean square error of the outliers were reduced by 44.56% and 33.33%, respectively. Also, the mean relative error and mean square error of the nearest neighboring points which are influenced by the outliers were reduced by 20.59% and 17.33%, respectively. Results indicated that the outliers of soil heavy metal could be effectively detected by the proposed method. Under the premise of adding finite sample size and analysis time, the quality of the survey data was improved and an effective tool was provided to carry out soil investigation at regional scale and guarantee the data quality.
Key words: soil heavy metal; outlier data; check method; cross-validation; prediction accuracy
Fig. 1 Distribution of soil samples in Beijing图1 北京市土壤采样点分布 |
Tab. 1 Check results of Cd outliers表1 Cd元素异常数据校验结果 |
行政 单元 | 样品 数量 | 空间自 相关法 | 极差法 (数理统计) | 极差法 (背景值) | 空间自相关法 -极差法联合 |
---|---|---|---|---|---|
北京 | 727 | 100 | 33 | 70 | 34 |
注:联合校验的异常点取空间自相关法与2种极差法校验结果的交集部分 |
Fig. 2 Distribution of outliers detected by mathematical statistics method图2 数理统计校验异常点分布 |
Fig. 3 Distribution of outliers detected by background value method图3 背景校验异常点分布 |
Fig. 4 Distribution of outliers detected by spatial autocorrelation method图4 空间校验异常点分布 |
Fig. 5 Distribution of outliers detected by combined method图5 联合校验异常点分布 |
Fig. 6 Comparison graph of Cd outliers between the original results and re-analysed results图6 Cd异常点原始数据与复测数据含量对比图 |
Fig. 7 Diagram of mean relative error and its variation图7 平均相对误差及其变化示意图 |
Fig. 8 Diagram of mean absolute error and its variation图8 平均绝对误差及其变化示意图 |
Fig. 9 Diagram of root mean square error and its variation图9 均方根误差及其变化示意图 |
The authors have declared that no competing interests exist.
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