Clustering Earth Science Data: Goals, Issues and Results

This work reports on recent work applying data mining to the task of finding interesting patterns in earth science data derived from global observing satellites, terrestrial observations, and ecosystem models. Patterns are "interesting" if ecosystem scientists can use them to better understand and predict changes in the global carbon cycle and climate system. The initial goal of the work reported here (which is only part of the overall project) is to use clustering to divide the land and ocean areas of the earth into disjoint regions in an automatic, but meaningful, way that enables the direct or indirect discovery of interesting patterns. Finding "meaningful" clusters requires an approach that is aware of various issues related to the spatial and temporal nature of earth science data: the "proper" measure of similarity between time series, removing seasonality from the data to allow detection of non-seasonal patterns, and the presence of spatial and temporal autocorrelation (i.e., measured values that are close in time and space tend to be highly correlated, or similar). While we have techniques to handle some of these spatio-temporal issues (e.g., removing seasonality) and some issues are not a problem (e.g., spatial autocorrelation actually helps our clustering), other issues require more study (e.g., temporal autocorrelation and its effect on time series similarity). Nonetheless, by using the K-means as our clustering algorithm and taking linear correlation as our measure of similarity between time series, we have been able to find some interesting ecosystem patterns, including some that are well known to earth scientists and some that require further investigation.