Dr. Dimitra Kitsiou Profile

Dr. Dimitra Kitsiou

at Univ of the Aegean

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Proceedings Article | 19 June 2015 Paper

Delineating sea surface water quality regions from remotely sensed data using textural information

Phaedon Kyriakidis, George Vasios, Dimitra Kitsiou

Proceedings Volume 9535, 95351W (2015) https://doi.org/10.1117/12.2192565

KEYWORDS: Water, Ocean optics, Oceanography, Oxygen, Remote sensing, Sensors, Data modeling, NOx, Modulation, Spatial resolution

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The delineation of ocean regions with similar water quality characteristics is an all important component of the study of marine environment with direct implications for management actions. Marine eutrophication constitutes an important facet of ocean water quality, and pertains to the natural process representing excessive algal growth due to nutrient supply of marine systems. Remote sensing technology provides the de-facto means for marine eutrophication assessment over large regions of the ocean, with increasingly high spatial and temporal resolutions. In this work, monthly measurements of sea water quality variables – chlorophyll, nitrates, phosphates, dissolved oxygen – obtained from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) with spatial resolution 0.125 degrees for the East Mediterranean region over the period January 1999 to December 2010, are used to define regions or zones of similar eutrophication levels. A novel variant of the K-medoids clustering algorithm is proposed, whereby the spatial association of the different variables (multivariate textural information) is explicitly accounted for in terms of the multivariate variogram; i.e., a measure of joint dissimilarity between different variables as a function of geographical distance. Similar water quality regions are obtained for various months and years, focusing on the spring season and on the qualitative comparison of the traditional and proposed classification methods. The results indicate that the proposed clustering method yields more physically meaningful clusters due to the incorporation of the multivariate textural information.

Proceedings Article | 29 October 2007 Paper

Evaluation of spatial interpolators in the framework of a geographical information system: a case study using oceanographic data

D. Kitsiou, T. Nitis, M. Kostopoulou, N. Maravelakis, G. Maneas

Proceedings Volume 6749, 67490C (2007) https://doi.org/10.1117/12.738209

KEYWORDS: Error analysis, Carbon, Oceanography, Geographic information systems, Water, Geography, Associative arrays, Ecosystems, Accuracy assessment, Environmental monitoring

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Spatial interpolation methods are widely applied in marine studies to evaluate the spatial distribution of oceanographic parameters and inter-compare time series of maps of selected variables. A variety of such methods are nowadays available and therefore, selection of the most appropriate for a specific case study is not an easy task. Within geography and other spatially oriented disciplines, and most of the times in the framework of a Geographical Information System, several attempts have been carried out to assess the efficiency of various spatial interpolators using diverse methodologies. In this paper, an attempt was carried out to evaluate the accuracy of spatial interpolators for mapping the distribution of organic carbon (weight %), an important indicator of marine sediments in the marine environment. Measurements of organic carbon were carried out in a network of 20 sampling sites in the Gulf of Gera, which is representative of a semi-enclosed and shallow marine ecosystem at the south-eastern part of the island of Lesvos, Greece. For the interpolators under study, the cross-validation error was calculated at each sampling station and calculation of the RMSE (root-mean-square error), the MAE (mean-absolute error) and the MBE (mean-bias error) was carried out to assess the accuracy of their performance. The results revealed the most appropriate interpolator for the given dataset which was then applied to develop the thematic map of the spatial distribution of organic carbon. Discussion on the potential increase of the surface accuracy is also carried out.

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