In the world of technological innovation, there usually comes a time where an invention crosses over from cutting-edge, into the mainstream, from being a great concept, into a greater reality. UAV LiDAR is one such technology. What could be better than mobile LiDAR? Affordable airborne LiDAR, of course!
The world of surveying covers such a wide range of tasks and topics that it’s impossible to cover all the potential applications of UAV LiDAR. From environmental surveys monitoring coastal erosion to large-scale surveys needed to develop the smart cities of the future – the scope of this technology is huge. But why? The answer is in the data.
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Photogrammetry vs LiDAR
Photogrammetry – Uses pictures to assume measurements based on an algorithm
LiDAR – Uses pulsed light from a laser to calculate measurements based on global positioning
Pretty much any drone, with a camera, can be used to create aerial maps. Photogrammetry software such as Pix4D allows the creation of geo-referenced data sets in the form of Orthophotos or Digital Elevation Models (DEMs) enabling accuracies of around 3cm. This technique is great for small-scale mapping projects and has been used to great effect in some high-profile projects such as mapping the statue of Christ the Redeemer in Rio.
Photogrammetry is a great way to lower the costs of carrying out simple surveys but what happens when you need more from your data? Greater accuracies, more detailed measurements, the ability to classify assets or remove obstructions? This is where UAV LiDAR comes in.
What is LiDAR?
Light Detection and Ranging (LiDAR) systems work in a similar way to sonar and radar but use light instead of sound or radio waves to measure distance. LiDAR units throw out pulsed light from a laser which calculates the distance by measuring how long it takes to be reflected back to the unit. Some LiDAR scanners measure around 1,000,000 ‘returns’ per second, enabling incredibly accurate 3D models to be created, with accuracies of around 5mm.
The data collected via a LiDAR scanner is used to create a point cloud – a collection of millions of data points which together build a three-dimensional representation of a target object or area. Scanners can be mounted to vehicles, aircraft and even worn on a backpack to enable large scale areas to be mapped in minutes.
Another reason LiDAR has become so popular with surveyors is the ability to deliver results even where there is dense vegetation blocking the view to the ground. This can create noisy elevation models in photogrammetry, making LiDAR the ideal choice for environmental mapping, forestry applications and even surveys in urban areas.
What’s So Special About UAV LiDAR?
Drones, or UAVs, are already revolutionising data and imagery capture across a range of sectors, owing to their ability to remotely capture aerial footage without the need for expensive helicopter or aeroplane flights. Hiring a helicopter can cost in the region of £1000 per mile covered. Add in the cost of a laser scanner and you need to have a hefty budget before you even start processing the data.
Airborne LiDAR projects can be prohibitively expensive due to these high mobilization costs. UAV LiDAR gives the operator the ability to rapidly survey small-scale and larger areas in a more cost-effective way. Drones can be deployed quickly, in the immediate vicinity allowing for surveys to be carried out without having to find a pilot, file flight plans and navigate to the surveying site making the technology perfect for emergency or time-sensitive situations.
It’s also safer to use a UAV LiDAR system. In the past, surveying a highway or railway line has meant ground crews being exposed to fast-moving traffic or trains. Terrestrial laser scanners also required multiple setups to cover large areas meaning that crews were either exposed to hazardous situations for longer, or roads and rail networks had to be suspended while surveys were carried out. Mobile mapping systems all but remove this risk by allowing data to be captured remotely. UAV LiDAR systems remove the risk entirely. As long as the drone remains in visual line of sight, a pilot can scan an area without having to be physically present.
Conducting surveys of high structures such as power lines and masts have long been an expensive and daunting task due to safety risks and the level of detail needed. These complex structures can be damaged by environmental conditions, wear and tear and even birds. Using a UAV LiDAR system means that the surveyor stays on solid ground yet is still able to collect enough data to build an accurate 3D representation of the infrastructure network, regardless of surrounding vegetation. You can also combine thermal imaging with a UAV LiDAR system to enable hotspots on powerlines to be identified rapidly before any serious consequences arise.
One of the greatest benefits of LiDAR is the ability to scan through dense vegetation. Photogrammetry relies on the ability to see the ground to calculate measurements accurately to create a digital terrain or elevation model. LiDAR is the only technology which allows DTMs & DEMs to be created even where there are trees or dense vegetation in the way.
UAV LiDAR is leading the way for agricultural and forestry businesses looking for a way to cost-effectively monitor carbon stocks and crops. UAV LiDAR enables forestry surveys to be conducted more quickly, giving landowners and operators access to data which would otherwise take months to collect. Although data can be enhanced by matching a ground and aerial scan, the location, count, height and volume of trees can be calculated in one single pass of a UAV.
UAVs also have great potential for vegetation mapping in urban areas thanks to the ability to capture ultra-high-resolution imagery at a low altitude. When combined with LiDAR data, a clear and precise map can be created showing building elevations, infrastructure assets and the shape and texture of vegetation, allowing for classification of land covers and situational analysis. This can help planners and maintenance crews to prioritise conservation efforts or removal of encroaching shrubs and bushes on highways, streets and railway lines.
What’s the Big Deal About Data?
Big data is one of the most commonly used buzz-phrases in the tech and information sector. Essentially, the term ‘big data’ covers any extremely large data set which can be ‘analysed computationally to reveal patterns, trends, and associations’. Data from a UAV LiDAR system can run in to terabytes thanks to the millions of points, or returns, collected by the scanner. This makes any information collected infinitely useable by various stakeholders.
In 2015, the Environment Agency released their airborne LiDAR datasets under the Open Defra framework. This data covers around 72% of England’s surface and is available to download under an Open Government Licence. This data is currently being used for flood planning (the Environment Agency’s original purpose for collection), landfill maps and heritage surveys, such is the scope of the data collected.
Data from a UAV LiDAR system also makes light work of asset classification. Whether you are surveying a construction site, major transportation network or a sports ground, software is available to identify and classify specific features. Multiple targets can also be identified so that land markings, traffic signs and even the roofs and windows of buildings can be extracted or removed from the visualisation. Clever stuff!
Both UAV and LiDAR developers are constantly striving to improve system integrations. At one stage, laser scanners were too heavy to be lifted by anything other than a fixed wing UAV, making UAV LiDAR ridiculously expensive. Now, with payload capacity increases and the shrinking weight and size of LiDAR scanners, there are a few options on the market for affordable UAV LiDAR systems. Speak to one of our surveying experts to find out more.
Thinking of using drones for surveying? Take a look at the new DJI Matrice 210 RTK – designed to tackle the most difficult surveying tasks in all weather.
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