Wreck of the Danish Schooner Hans Egede, Cliffe, Kent - 3D model

Access all areas: drones in the tidal zone

Peter Rauxloh
20.08.2015

Our newest team at MOLA is working on the CITiZAN project. CITiZAN stands for the Coastal and Intertidal Zone Archaeological Network, and with a core team in London and out-stations in York and Portsmouth, the project galvanises support from community groups across England to record and monitor archaeological sites that are at risk from erosion, along our coastline and tidal estuaries.   

The geology and topography of these areas gives rise to a variety of conditions, with some being more treacherous than others. The intertidal zone has to be treated with respect and the quality of footing, tidal range and speed of inundation are all important variables to consider if you are to work there safely. There are of course some coastal sites that remain inaccessible at low tide and this is where the use of Small Unmanned Aircraft (SUA) is proving to be rather useful. 

Our drone, or SUA, captures multiple overlapping vertical images, which are processed to produce an orthogonal image, (an image in which the viewer is looking directly down). Our SUA is being used in two main situations for the CITiZAN project, the first being the most obvious, to beat the tide.

The speed with which an area can be flown and surveyed by an SUA means that large areas of foreshore can be mapped in a single tide window. To prepare for a flight, targets are placed on the ground, which will be visible in the images and their position accurately recorded using a GPS (Global Positioning System). These targets, known as Ground Control Points (GCPs), are used to provide a scale and real-world position when the orthogonal image is processed, allowing it to be accurately overlain on other geo-referenced mapping. More importantly it allows for the features shown on the image to be accurately measured and quantified, of vital importance in any monitoring exercise.

The second situation is where a particular target is not reachable on foot.  In this instance the aircraft flies around the archaeological feature to capture the images. For obvious reasons vertical imagery is less able to capture the detail of vertical surfaces, whereas images taken at an oblique angle can. This is particularly useful for archaeological features standing proud on the foreshore, such as ship wrecks. The aircraft can fix on the wreck as its target, retreat from it, and then fly in circles at a constant distance with the camera continually facing the target.

Please contact Dr. Peter Rauxloh if you would like to know more about our aerial survey and monitoring services.

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