FAQ
Airborne LiDAR (Light Detection and Ranging) is a fast, accurate method of obtaining three-dimensional data for creating Digital Surface Models using LiDAR technology. With an integrated camera, RGB images can be supplemented by LiDAR data to provide a comprehensive evaluation of ground information using an active sensor that uses lasers to measure distances to features and the ground.
Airborne LiDAR provides a highly detailed, geo-referenced and accurate point cloud. As well as traditional mapping products, this data can be used to extract valuable information, such as Digital Elevation Models (DEM) and Digital Terrain Models (DTM). Airborne LiDAR typically allows for the collection of multiple pulses, which enables the collection of digital elevation data of both trees as-well as the ground beneath simultaneously.
A laser creates a light pulse which is then projected to a mirror, ultimately reaching a ‘target’ usually a ground based object. As the laser travels down until it collides with an object, it is reflected back to the system. Determining the distance from its starting point becomes achievable thanks to a mathematical equation that takes the speed of light as constant. This measurement gives us the height, also known as Z data point, of an entity. To obtain more details about such entity’s longitude and latitude (X and Y data points), Global Positioning Systems are used concomitantly. In addition, an inertial measurement unit on board can bring digital positional information regarding pitch, yaw and roll dimensions to us.
Recent advances in LiDAR technology have made it possible to acquire data rapidly from planes and helicopters thousands of feet up, as well as from the ground level with UAVs. This is particularly useful for surveying hazardous or unapproachable areas where traditional methods are impractical. An additional benefit is that airborne surveys can be conducted without any health or safety risks for those involved, as the lasers pose no threat to humans.
LiDAR systems available today include the Leica CityMapper 2, Teledyne Optech Galaxy T-2000 and RIEGL VQ-1560-II, these are capable of functioning at impressive speeds and heights – up to 4 million pulses per second and 7,500 metres respectively. Moreover, they are able to capture multiple returns per pulse or even collect unlimited returns by digitising the full waveform.
Systems designed for small UAVs have also advanced rapidly – they can generate hundreds of thousands of points every second, allowing them to record hundreds of points in each square meter when flown at an appropriate altitude and speed.
Such systems consist of a combination of components which are generally referred to as the “system”; these sometimes may differ in specific details but usually include a laser scanner, inertial navigational system (INS) and cameras.
Laser scanners are sophisticated systems which emit an array of timed laser pulses and measure the reflected return pulse. This information is used to detect the elapsed time or phase shift, as well as the strength of the returning light intensity. These systems usually feature a fixed laser source, with the scan action created by rotating or oscillating mirrors.
Alternately, fibre arrays can be used to generate a scanning pattern. Advanced airborne lasers allow for multiple returns from each outgoing pulse, as well as a “Full Waveform” return for further processing. The resulting data gathered from this process can be used to create rich 3D models of features and landscapes.
However, it’s important to note that the last pulse return is not necessarily from the ground and must be verified through ground truth data.
An Inertial Measurement System (INS) allows for the successful positioning and orientating of the system during data capture by the Laser Scanner is essential to obtaining a precise final output.
The INS combines data from GNSS receivers and an Inertial Movement Unit (IMU) in order to form highly accurate estimates of the trajectory – commonly known as SBET (Smoothed Best Estimate of Trajectory).
Typically, this involves taking advantage of recent GNSS base station technology for differential processing.
Most modern airborne LiDAR systems have a camera system to collect simultaneous imagery, which can then be used to carry out a number of tasks:
- Produce vector orientated images
- Produce true orthographic images
- Colourise the point cloud
The use cases and effective applications of Airborne LiDAR is expanding, especially as AI and Machine Learning becomes more commonplace.
In principle however, any application that requires volumetric or three-dimensional data of a wide-area and which can be seen from above is suitable, these include:
- City planning
- Agricultural mapping
- Change detection
- Transmission Line mapping
- Floodplain surveying
- River & Coastal monitoring
