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Auflistung nach Autor:in "Niska, Harri"

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  • Konferenzbeitrag
    Missing Data Toolbox for Air Quality Datasets
    (Environmental Communication in the Information Society - Proceedings of the 16th Conference, 2002) Kolehmainen, Mikko; Junninen, Heikki; Niska, Harri; Patama, Toni; Ruuskanen, Anna; Tuppurainen, Kari; Ruuskanen, Juhani
    The objective of the study was to find a useful missing data imputing method for air quality forecasting applications. The univariate methods studied were the linear interpolation, spline and nearest neighbour (univariate) interpolation. Multivariate methods studied were multivariate nearest neighbour (NN), Self-Organising Map (SOM) and Multi-Layer Perceptron (MLP). Additionally, a new approach was developed where univariate methods were combined with multivariate methods in order to utilise the best properties of both approaches. The results in general showed that the best overall performance can be achieved by combining univariate and multivariate methods and that the way of combining is dependent on the variable inspected. Based on these results a Missing Data Toolbox (MDT) with a Graphical User Interface (GUI) in Matlab environment was created. The MDT encapsulates the different algorithms and enables the treatment of missing data in a coherent way. The MDT and GUI were tested on Windows and Linux environments.
  • Konferenzbeitrag
    Self-organizing maps and Sammon’s mapping in environmental informatics and bioinformatics
    (Sh@ring – EnviroInfo 2004, 2004) Kolehmainen, Mikko; Hiltunen, Teri; Niska, Harri
    The aim of this study was to evaluate the usability of self-organizing maps (SOM) and Sammon’s mapping in analysing data originating from processes of environmental informatics and bioinformatics. The methods used are shortly introduced. The results show that the combination of SOM and Sammon’s mapping has great potential in data exploration, and can be used to reveal important features of the measurement techniques used, reveal new information about phenomena studied earlier, speed up research work at laboratory level, act as a hypothesis generator for directing traditional research, and supply clear and intuitive visualization of the environmental phenomenon studied.