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Dealing with outliers and censored values in multi-element geochemical data: a visualization approach using XmdvTool
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
2005 (English)In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 20, no 2, 341-352 p.Article in journal (Refereed) Published
Abstract [en]

 Dealing with geochemical data also means coping with their underlying limitations that are related to sampling, analytical techniques, and other characteristics of the data. This paper discusses the issue of data cleaning, using a regional geochemical dataset of 6 heavy metals in glacial till. Interactive data manipulation techniques provided in the freeware visualization system XmdvTool were used for exploring both metal concentrations reported as under the detection limit, and high or extreme values (outliers) in the dataset. The proposed integrated visual evaluation (IVE) approach for selective removal of outliers outperformed simple removal of the highest concentrations of metals, showing that existing spatial multi-element fingerprints in data could be recognized and preserved by IVE. The uniqueness of visualization is in simultaneous display of both multivariate and spatial information. Being simple and interactive, integrated visual evaluation can be recommended as a valuable complementary tool in cleaning and analysing multielement geochernical data.

Place, publisher, year, edition, pages
2005. Vol. 20, no 2, 341-352 p.
Keyword [en]
Chemical cleaning, Concentration (process), Data reduction, Heavy metals
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:kth:diva-5028DOI: 10.1016/j.apgeochem.2004.08.006ISI: 000227045100009Scopus ID: 2-s2.0-12344311443OAI: oai:DiVA.org:kth-5028DiVA: diva2:7635
Note
QC 20100609Available from: 2005-04-18 Created: 2005-04-18 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Visualization, integration and analysis of multi-element geochemical data
Open this publication in new window or tab >>Visualization, integration and analysis of multi-element geochemical data
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

generated large databases containing information on the concentrations of chemical elements in rocks, surface sediments and biogeochemical materials. Regional geochemical data being imprecise, multivariate, spatially auto-correlated and non-normally distributed pose specific problems to the choice of data analysis methods. Commonly several methods are combined, and the choice of techniques depends on the characteristics of data as well as the purpose of study. One critical issue is dealing with extreme data values (or outliers) in the initial stages of analysis. Another common problem is that integrated analysis of several geochemical datasets is not possible without interpolating the point data into surfaces. Finally, separation of anthropogenic influences from natural geochemical background in the surface materials is an issue of great importance for environmental studies.

This study describes an approach to address the above-mentioned problems by a flexible combination and use of GIS and multivariate statistical techniques with high-dimensional visualization. Dynamically linked parallel coordinate and scatterplot matrix display techniques allow simultaneous presentation of spatial, multi-element and qualitative information components of geochemical data. The plots not only display data in multi-dimensional space, but also allow detailed inspection of the data with interactive multi-dimensional brushing tools. The results of the study indicate that these simple high-dimensional visualization techniques can successfully complement the traditional statistical and GIS analysis in all steps of data processing, from data description and outlier identification through data integration, analysis, validation, and presentation of results. The outcomes of the study include: a visual procedure towards intelligent data cleaning where potentially significant information in very high element concentrations is preserved, methods for integration and visual analysis of geochemical datasets collected in different grids, estimation of geochemical baseline concentrations of trace metals in till geochemistry of southeastern Sweden, use of multi-element spatial fingerprints to trace natural geochemical patterns in biogeochemistry, and a new graphical approach to present multi-element geochemical data summaries and results from numerical analysis.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005
Series
Trita-LWR. PHD, ISSN 1650-8602 ; 1018
Keyword
Earth sciences, GIS, interactive visualization, glacial till, biogeochemistry, metals, southeastern Sweden, Geovetenskap
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-169 (URN)91-7178-014-9 (ISBN)
Public defence
2005-04-21, Kollegiesalen, Valhallavägen 79, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100609Available from: 2005-04-18 Created: 2005-04-18 Last updated: 2010-06-09Bibliographically approved

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