Natural Resources Wales contracted Exegesis to undertake an aerial survey of several sites, in connection with pending enforcement/legal action. We were asked to provide evidence of materials located at the site, with a particular emphasis on determining the quantity of material.

The survey was undertaken by our mini-plane less than 24 hours after the initial request was made. In order to attain the highest level of spatial accuracy, ground control points were taken with a high precision GPS unit. The images were orthorectified and mosaicked to create a single image using Pix4UAV advanced processing software.

We also used Pix4UAV to generate a digital surface model (DSM) to enable 3D analysis to be undertaken. This DSM was compared against lidar data, which provided a baseline height for the site before the addition of material. The lidar data was subtracted from the DSM to give the change in height, which was then analysed to determine the volume of additional material within discrete patches identified from the aerial photography. The volumetric analysis was undertaken using GRASS and verified with MapInfo Engage 3D.

The aerial images, DSM and outputs of the analysis were provided to the client, along with a report describing the methodology used and the results.

Further information from Crispin Flower.