We have been dabbling with a remarkable source of free topographical data provided by the Environment Agency which makes available the data arising from LIDAR surveys. Light Detection and Ranging (LIDAR) is an airborne mapping technique, which uses a laser to measure the distance between the aircraft and the ground, which when combined with information from the aircraft’s navigational system,provides a remarkable view of the ground surface, sometimes revealing features not readily apparent. For Christchurch, such data is available at a resolution of 50cm and we have been using the processed Digital Terrain Model (DTM) which is produced from the basic Digital Surface Model (DSM) obtained during survey by filtering out by software the heights of vehicles, buildings and vegetation.
For what it’s worth, the illustration above shows the result of processing the LIDAR data within a Geographical Information System (GIS), using colour to show ground elevation and hill-shade to enhance any features. The colour scheme has set so as to enhance the number of levels associated with the lower, riverside and meadow areas around Millhams. We found this article very useful in processing the data. The map has been annotated such that members can find their way around it – Millhams Street and Ducking Stool Lane are apparent on the map. Unfortunately there is little new which can be gleaned from the map , but with patience the presence of the watercourses and channels running across near the site can be discerned.