What are Airborne Laser Scanners and how they work?

What are Airborne Laser Scanners and how they work?

What are Airborne Laser Scanners and how they work?

Introduction

Laser scanning is an emerging technology for data capture that has significantly expanded its area of use and has been a serious competitor to other survey methods. Airborne laser scanning showed strong advancement in the 1990s due to rapid technological development, the increased accuracy of global positioning systems and the improvement of demands for even more precise digital surface models. Airborne laser scanning, also widely known as the LiDAR (Light Detection And Ranging), is an effective remote sensing technique used to monitor the earth’s surface, especially the landscape of large terrain areas and objects that appear on it. Airborne Laser Scanning Technologies are LiDAR structures that can be installed on aircraft. NASA used the first lidar remote sensing devices in the 1970s to chart the Arctic and Antarctic ice-covered areas. LiDAR (Laser Imaging Detection and Ranging) technology enables the automated processing of 3-dimensional data at a high rate. Since the environmental conditions and illuminations hardly influence the measurements, laser scanning has become ideal for any survey, analysis or mapping.

miniVUX-2UAV airborne laser scanner

miniVUX-2UAV airborne laser scanner

Airborne Laser Scanners principle

As an efficient remote sensing device, Airborne laser scanning allows data to be easily collected from large areas. The resulting dataset is the basis for digital surface and elevation models. Integration of Airborne laser scanning with airborne imagery makes it possible to combine the point clouds and images and this in turn results in achieving a higher 3D product quality.

The fundamental working principle of this technology is as follows: the scanner produces a laser pulse in a predetermined path through the landscape and collects the reflected laser beam. Knowing the speed of light, it is possible to calculate the target distance. The laser scanner is placed on the UAV helicopter’s payload bay. The wide scanning angle makes it possible to optimally travel over the ground at a very low height and to inspect vertical structures such as walls or concrete dams. Scanning sideways is even doable.

Workflow:

  • Task flight preparation and checking to get the required point density from the laser scanner. Until heading out to the flight area, this can be achieved in the laboratory.
  • The payload is placed on the flight field to the UAV. After the initialization process is taken, the system is prepared for the test flight.
  • The laser scanner may be started and stopped during the flight. Scanner status and data about the INS / GPS system are constantly sent to the ground control station and differential GPS correction information is sent to the payload.
  • Laser scanning data and INS / GPS data are placed on board and recorded. It can be transferred to the computer of the ground control station upon landing.
  • Combining laser scan data and INS / GPS location information, the software package is used to analyze the point cloud.

The following subsystems are comprised of airborne laser scanning systems:

  • Laser detector and data storage system
  • INS/IMU (Inertial Navigation System / Inertial Measurement Unit)
  • GNSS (Global Navigation Satellite System)
  • GNSS ground station(s)

Time of Flight- Laser scanning is only a laser range finder. It generally measures a distance by firing a laser beam to an object and measuring how long it takes to bounce back with that laser beam. knowing the speed of light (laser beam) and measuring the time the distance can be easily calculated by multiplying the time by the speed of light and dividing it by 2.

Phase-Based – Using a laser energy continuous pulse released from the scanner. Then the scanner calculates the returned laser energy’s phase change to determine distances.  All else is the same as the flight scanner time.  Phase-based scanners can collect data at a speed of up to one million points per second. Their distance, however, is about 80 meters.  For industrial plant work and building interiors, phase-based scanners are most suitable.

Conclusion

Airborne Laser Scanning (ALS, also known as LiDAR–Light Detection And Ranging) is a pioneering technique for precise and effective mapping of Earth’s topography, a measurement device in which light pulses (most frequently generated by a laser) are emitted from an aircraft-mounted instrument and guided to the surface in a scanning pattern. Airborne laser scanning-are arrays of points recorded on the aircraft panel by the device called LIDAR (Light Detection and Ranging). In very short periods of time, LIDAR sends a laser light beam and records the positions of its reflections from objects on the ground. The detector, mounted on an airplane, emits a high-frequency laser beam to the Earth at a very high pulse speed of hundreds of thousands of measurements per second, each reaching the target surface and transferring a small portion of its energy back to the sensor. A sensor receiver detects the transmitted laser pulses from the surface of the Earth or from ground objects.

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