Conference Contribution Details
Mandatory Fields
Scarrott, R.G., O' Connor, B., Dwyer, N., Cawkwell, F.
Irish Earth Observation Symposium 2011
Characterising landcover using vegetation seasonality profiles determined from satellite imagery.
Johnstown Castle, Co. Wexford, Republic of Ireland
Oral Presentation
2011
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0
Optional Fields
17-NOV-11
18-NOV-11

Land cover classification has traditionally been based on imagery from one or two points in time. The pan-European CORINE land cover classification system, for example, is largely derived from optical datasets acquired at most twice in one year. These temporal restrictions fail to fully capture and indicate fluctuations in vegetation over the season, which can potentially result in misclassification of land cover surfaces. A lack of information on seasonal variability within a land cover class, for example different pasture management practices, can further limit the use of the data.

This research explored an alternative approach to deriving information about Irish landcover, using the seasonal cycle of vegetation growth retrieved from a time-series of medium resolution satellite imagery. The study used the Enhanced Vegetation Index (EVI) product for 2006 from the MODIS-TERRA satellite sensor. A time-series of 250m spatial resolution, 16-day composite EVI images was processed, using time-series analysis methods. The seasonal profile per pixel was first modelled using TIMESAT to reduce the effect of cloud interference, and modelled pixels were then clustered using a divergence-guided ISODATA clustering algorithm. This grouped pixels of similar seasonality together using a data-driven approach. A Jeffries-Mathusita threshold analysis was then applied to evaluate cluster distinctiveness.  

Clear patterns in vegetation seasonality were detected across the island, with the Jeffries-Mathusita analysis identifying ten groups characterised by different seasonal profiles. Analysis of the seasonality pattern attributed to individual clusters within these groups revealed that certain areas exhibited two seasonal peaks in photosynthetic activity, with a marked decrease in activity in June/July. Subsequent comparison with the CORINE landcover 2006 dataset for the Republic of Ireland confirmed their location within “pasture” areas. Land use such as silage cutting, practiced in intensively-managed grasslands, is suggested as the most likely cause of the detected double-season cycle. This finding demonstrates the potential of time-series analysis for improving our knowledge of seasonal attributes of landcover in Ireland, and of grassland management in particular. Furthermore, the finding has important implications for carbon accounting under Ireland’s commitments to the Kyoto protocol.

Environmental Protection Agency under the Climate Change Impacts on Phenology programme.