Everything you need to know about surveying with drones

The past decade has seen the emergence of drones that have the ability to provide very high spatial resolution imagery to assist in mapping and surveying. So what is drone data and how does it work?


Drone data is really “aerial data” and can be split into two camps: Photogrammetry and LiDAR.


Drone data capture works similarly to other aerial capture methods, whereby high-resolution cameras and thermal/multispectral sensors attached to the drone are flown over or around an area or object of interest collecting data. The differentiating factor for drones is that they can get closer than other aerial methods, which in most cases leads to greater levels of spatial accuracy.


The most widespread use of drones in remote sensing is photogrammetry due to its low cost and weight requirements (all you need is a camera and GNSS). These often come with added safety and efficiency benefits over the heavier, more expensive systems.


Drone mounted LIDAR systems are relatively new to the market. They’re also expensive and require drones with greater payloads (decreasing efficiency and increasing potential risk, leading to higher regulatory barriers to their use). However, they are gaining in popularity as they offer a lot of versatility and greater accuracy.



Photogrammetry


Modern photogrammetry is a passive form of remote sensing that uses 2D images combined with geolocation to create a base dataset. For photogrammetry to work, an object must be captured in multiple images (at least three) from different angles. The images are then processed using complex computer vision algorithms to produce 2D and 3D datasets.


Drone derived photogrammetry is produced using survey-grade fixed-wing drones designed for large topographical surveys. Because the sensors are light (<200g) fixed-wing drones can survey up to 5km2 per day and carry onboard RTK GPS sensors that help produce (and correct) outputs for survey and engineering use cases.


Data captured using drone photogrammetry and visualised in Sensat's platform



LiDAR


Light detection and ranging (LiDAR) uses lasers in a similar way to how radar uses radio waves to detect the position and geometric shape of an object. A pulse of light is emitted from the device and a sensor then detects how long it takes for the light to return. Modern LiDAR systems can produce millions of pulses per second, and each of these pulses creates a potential data point that can be turned into a ‘point cloud’.


Each method of capturing data will have its benefits and drawbacks. Delivering a project or managing an asset effectively will require you to procure multiple types of data during any single stage of its lifecycle, from design to management. It’s important you are able to procure the data that will have the largest impact. You need to make the right choice, balancing multiple factors.



The following questions should drive your priorities when considering accuracy level and which data capture method to use:

  • Why are you procuring data for your project or asset?

  • What information do you need?

  • How is this data going to be used?

  • At what stage of the project will you want to use this data?

  • What specific data outputs do you require to make decisions?


The pros and cons


Over the past decade, drones have become an important part of the data mix for infrastructure projects and management. They offer a good balance between accuracy, efficiency, and safety while still producing diverse, versatile datasets.


Let's take a look at some of the benefits and drawbacks of a drone photogrammetry data capture.



Pros:

  • High quality, photorealistic outputs that are understandable and accessible

  • Regular and repeatable data capture possible

  • Good spatial resolution and accuracy

  • Light-weight and safe to operate

  • No need for boots on the ground

  • Medium area coverage (~2.5sqKM per day)

  • Minimal land access required

  • Can operate in hazardous environments


Drawbacks:

  • Cannot penetrate vegetation

  • Susceptible to distortion due to weather conditions

  • Regulatory limitations on operational capabilities



During the past three years, drones have moved from being a secondary piece of a project’s data mix to being a primary data gathering method. That’s because, in the right hands, drones can collect and produce reliable data. Multiple studies have demonstrated the reliability and accuracy of drone data leading to more widespread adoption in the industry.



Staying safe on-site during the pandemic


Strict safety measures are being put in place on all construction sites and building projects to ensure people are kept safe. The industry is highly safety-conscious and, although it will be challenging to implement social distancing measures, ensuring safe working practices is at the top of the industry’s priorities.


Industry leaders are adopting new remote work technologies and procedures to limit the impact of the pandemic on their employees. Utilising drones to remotely capture and monitor site data is one-way companies throughout the UK are getting employees safely back to work.





Other things to consider


It’s important to note that drones are not the only silver bullet for project data. They must be used within a well planned and agreed-upon data mix that delivers on a project’s objectives. And ultimately, the data collected by these platforms must be interoperable and easy to access. Without visualisation platforms such as Sensat’s, the data mix can quickly become data silos for a project.



Sensat prides itself on being industry leaders in drone data capture. Through the use of drones, we are able to collect and visualise up-to-date and highly accurate data that is valuable throughout the different design and construction stages.


On the Sensat website, you can find a whole page dedicated to free educational case studies, webinars, reports and tutorials to help you plan, build and manage your projects. Visit www.sensat.co.uk/resources to learn more.


To see Sensat's drone data quality for yourself, request sample data at: data.enquiries@sensat.co.uk. Alternatively, learn more about Sensat's data services and what we can do to support your project here.