Updating the Phase 1 habitat map of Wales, UK, using satellite sensor data

The Phase 1 Survey is the most comprehensive and widely used national level map of semi-natural habitats in Wales. However, the survey was based largely on field survey and was conducted over several decades, before being completed in 1997. Given that resources for a repeat survey were limited, this study has used an object-orientated rule-based classification implemented within eCognition of multi-temporal satellite sensor data acquired between 2003 and 2006 to map semi-natural habitats and agricultural land across Wales, thereby allowing a progressive update of the Phase 1 Survey. The classification of objects to Phase 1 habitat classes was undertaken in two steps; firstly the landscape of Wales was divided into objects using orthorectified SPOT-5 High Resolution Geometric (HRG) reflectance data (10 m spatial resolution) and Land Parcel Information System (LPIS) boundaries. A rule-base was then developed to progressively discriminate and map the distribution of 105 sub-habitats across Wales based on timeseries of SPOT HRG, Terra-1 Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Indian Remote Sensing Satellite (IRS) LISS-3 data, derived datasets (e.g., vegetation indices, fractional images) and ancillary information (e.g., topography). The rules coupled knowledge of ecology and the information content of these remote sensing data using a combination of thresholds, Boolean operations and fuzzy membership functions. A second rule-base was then developed to translate the more detailed sub-habitat classification to Phase 1 habitat classes. Indicative accuracies of the revised Phase 1 mapping, based on comparisons with the later Phase 2 survey (for selected habitats), were >80% overall and typically between 70% and 90% for many classes. Through this exercise, Wales has become the first country in Europe to produce a national map of habitats (as opposed to land cover) through objectorientated classification of satellite sensor data. Furthermore, the approach can be adapted to allow continual monitoring of the extent and condition of habitats and agricultural land. © 2010 International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS). Published by Elsevier B.V. All rights reserved. pre-defined land use and land cover classes. Mapping was largely from vantage points although unregistered aerial photographs viewed in stereo were used to support the ground survey, particularly in the uplands (JNCC, 2007). The level of detail was also variable between counties with, for example, hedgerows mapped in Powys but not in other counties. The Phase 1 Survey mapped 103 distinct habitats (Table A.1) and was first released as a series of paper maps, then as a scanned raster layer, and finally as a digital layer in the early 2000s. Today, the original Phase 1 Survey is still being used as the primary habitat map for Wales as it has proven difficult and expensive to update. However, updates are needed as significant changes in semi-natural vegetation have subsequently occurred across the Welsh landscape, largely because of changes in agriculture and forestry activities, practices and policies. Further changes are anticipated as a consequence of climate change and associated mitigation strategies (Berry et al., 2008). 0924-2716/$ – see front matter © 2010 International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS). Published by Elsevier B.V. All rights reserved. doi:10.1016/j.isprsjprs.2010.09.004 Richard Lucas , Katie Medcalf , Alan Brown , Peter Bunting , Johanna Breyer , Dan Clewley , Steve Keyworth , Philippa Blackmore