Blog: Is a UAV accurate enough to replace a terrestrial survey?

Paul Aldersley, a graduate from Plymouth University, now working at the UK Hydrographic Office, discusses the findings from his recent project that formed the basis of his dissertation.

As part of my studies for a BSc in Ocean Exploration at Plymouth University, I recently completed a project on beach surveys. There are several reasons for surveying beaches: monitoring sea levels; coastal erosion; and researching beach processes amongst other things. In essence, beaches change frequently so surveys must be repeated on a regular basis. So for my project, I chose to compare aerial and terrestrial equipment for this application.

One potential advantage of aerial surveys is a significant time saving when compared to terrestrial, although until now they have been prohibitively expensive due to the use of manned aircraft. Unmanned Aerial Vehicles (UAVs), commonly called drones, have been recognised for several years as a much more cost effective alternative but their accuracy has been called into question. The need for a network of ground control points (GCPs) has also restricted the usefulness of UAVs, until now.

Topcon’s Sirius Pro UAV does not need GCPs and claims to have excellent accuracy too.

The aim of the project was to answer two questions: Was data collected by the Sirius Pro, without GCPs, of sufficient quality to suggest it as a suitable alternative to a terrestrial survey? And do UAVs offer any time saving advantages?

Finding the answers

To answer these questions I completed a digital photogrammetric survey of a suitable beach using the Sirius Pro then surveyed the same beach using terrestrial equipment and compared the results.

Topcon provided me with a Sirius Pro UAV and the expertise of Mat Kellett, a qualified UAV pilot. The terrestrial survey was completed by The Coastal Observatory Project and it goes without saying I couldn’t have completed the project without this support.

The comparison of the results of the two showed that using the Sirius Pro UAV is sufficiently accurate to be an alternative to a terrestrial survey. The terrestrial survey took five and a half hours whereas the aerial was completed in less than two hours. This was also aided by the fact that the Topcon Sirius Pro is the only UAV on the market that does not require GCPs and as such, it vastly reduces the set up time required to complete the job.

There are some considerations to keep in mind when using a UAV. It is well known that due to the limitations of water and photogrammetry it is not possible to get accurate results in the transition area between the surf and the beach. The survey also had to be completed over two flights to comply with CAA regulations as the pilot must be within 500m of the UAV at all times.

While the data download from the terrestrial survey was complete in a matter of minutes, the processing time from data capture to point cloud generation for both flights was several hours. This was, however, due to an average specification laptop being used. Most professional surveyors have access to a much higher spec PCs that would greatly reduce this time. That said, the download process is automated so the kit can be left to complete without any human input.

From evaluating both options, the project definitely demonstrates that, as well as capturing accurate data, the Sirius Pro is a great way of saving time on jobs and are specifically useful for beach surveys that need to be completed on a regular basis.