Water & Wastewater Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/515382
Project focus: Environmental management due to the river's fish population. Finally, the vast majority the river channel was not visible from the ground due to steep banks which were largely inaccessible. The use of a UAV allowed for an unobstructed view of the entire river channel without requiring personnel to actually climb into the channel, potentially putting them at risk. Method The survey involved two main aerial survey types – videography and elevation modelling – and was enhanced by elements of ground based survey work including photography and GPS measuring. The videography element of the aerial surveys was collected in two main formats: standard video and 360° videos. Both types of video were very useful in identifying potentially problematic areas of the river channel, such as areas where the bank reinforcements were damaged or where there was significant debris build up. The collection of the standard videos involved the UAV being flown directly in the river channel, with the camera operator directing the camera to focus on one bank of the river at a time. The video was streamed live back to the camera operator, allowing them to direct the UAV pilot, such as instructing them to fly closer to areas of interest. These videos were collected using a broadcast quality Panasonic Lumix GH3 mirrorless camera. This camera recorded full HD with up to 60 frames per second and was attached to the UAV by a camera mount which can be controlled with a precision of +/-0.05° around all three axes. The collection of the 360° videos involved mounting six wide-angle cameras beneath the UAV which have enough overlap between them to create a full 360° image. The cameras used for this were GoPro Hero 3s, recording in 1080p with 25 frames per second. This allows viewers to simultaneously see the condition of both banks as well as the river bed. The 360° camera mount on the six rotor UAV is a lightweight solution: with a maximum weight of just under 7kg, it allowed the project team to fly in controlled airspace without requiring permission from Air Traffic Control. Elevation Elevation models were produced using photogrammetry. This process involves taking a series of vertical photographs at pre-defined intervals to produce a dataset with exact levels of overlap. The geometry between matching points on different photographs was used to produce highly accurate elevation models. The accuracy of these models was achieved through capturing very high resolution imagery using the Canon 5D MK III full-frame DSLR, which has a resolution of 22.3 MP. Flying at 70m, this translated to a ground sample distance of 21.09mm. The accuracy was further enhanced by using a high specification ground GPS station (accurate to +/- 30mm) to georeference the elevation model. Conclusions The project was extremely successful in proving the viability of using UAVs to complete diverse aerial surveys of river banks in a time and cost effective manner whilst producing incredibly high quality data. The flexibility of these platforms allowed RAS to provide a broad overview of the site whilst enabling them to focus in on the finer details which contribute to this. Tom Gravett, Operations Manager at Remote Aerial Surveys, said: "UAVs are an ideal solution when data is required from hard to reach areas. In this case it was a river channel, but UAVs can access a whole host of other sites to carry out surveys & inspections, such as pipe line surveys, infrastructure inspections or even georeferenced aerial photography for asset management. "Essentially, UAVs are a means of delivering sophisticated image capturing equipment to locations that are hard to reach, in a quicker and more cost effective way. By using thermal or multispectral sensors for example, as well as traditional cameras, they are now solving a wide range of real business problems, delivering better data & imagery at a fraction of the present cost. "UAVs bring a whole new level to what is possible when capturing data & imagery, with elevation modelling for example, being just one really powerful application. The data captured by using a UAV mounted camera can produce 3D models that make a really engaging tool for communicating information about the landscape." An elevation model produced by photogrammetry • Innovations ● Two main aerial survey types - videography and elevation modelling – were used, supplemented by elements of ground-based survey work ● 360 degree video identified problematic areas of the river channel ● Six wide-angle cameras mounted under the UAV produced a full 360° image, recording 25 frames per second ● Flooding along the River Mole risks damage and disruption to key infrastructure in its catchment such as Gatwick Airport and the M25 motorway ● A detailed survey was required with high-resolution images captured at a low level, while the water was at its lowest ebb ● UAVs were ideal because much of the river channel was not visible from the ground due to inaccessible steep banks • Drivers 20 | JUNE 2015 | WWT | www.wwtonline.co.uk Six wide-angle cameras were mounted beneath the UAV to produce 360-degree images