Environment and Rural Affairs Monitoring & Modelling Programme - ERAMMP Report-56: Suitability of Satellite Data and LiDAR for Mapping Hedges

The Welsh Government (WG) uses data on hedges and field boundaries for a variety of purposes including scheme delivery, environmental monitoring and regulatory compliance. Hedge data are currently acquired mainly through a combination of aerial photography and field visits. Considerable cost savings may be possible, if optimising the use of satellite data enables the number of field visits to be reduced. This project explored the potential for high resolution satellite data to provide accurate spatial data on hedge location and length. A number of methods of hedge mapping were tested, including manually digitising hedges and more automated methods using Skysat Imagery Products data from Planet Labs Inc.1 and LiDAR. The key findings of the project were: A. Aerial photography was a better source of data for manually digitising hedges than the Planet Skysat data available for this project. This is because the aerial photography has higher spatial resolution (25cm compared to ~50cm) and the Planet Skysat data used in this project was collected in winter and was badly affected by shadows. Note, for the purposes of this project, only Planet Skysat data collected in the winter were available, however, it is highly likely that multi-temporal Planet Skysat data would improve results further. B. For two of the three sites, the spatial accuracy of the Planet Skysat data was too low to map hedges, without spending additional effort manually geo-correcting images. C. Automated methods using LiDAR show promise, but there are issues with producing a final ‘clean’ vector data set that require additional work. LiDAR-based methods could be deployed in a number of ways depending on requirements. D. Automated methods using LiDAR and aerial photography could be deployed in a number of ways depending on whether the aim is to measure some attributes of hedge condition, or hedge location and length. E. Methods using automated detection of new hedges using LiDAR data, followed up by manual checking against aerial photography, may be able to capture the best aspects of different approaches.