Aerial laser surveying is a technology aimed at the acquisition of 3D point group data (X, Y, and Z). It is used to create Digital Surface Models (DSM), which is one of the terrain representation methods currently available.
This data is applied to a wide range of fields, including disaster prevention, roads, erosion control, forests, agriculture, urban planning, and rivers.
PASCO has adopted aerial laser surveying technology as one of its acquisition technologies for spatial information since 2000. Today, in consideration of the density of acquisition points, as well as of the terrain conditions and surface area of the target, we are able to deal with various conditions through the use of aircraft with fixed wings (PASCO uses Cessna) and rotating wings (helicopters).
In computing the position coordinates of laser points cloud data, in a way similar to technology for aerial surveying, the flight trajectory of the aircraft is obtained through GPS/IMU (a measuring system for position and posture). The laser transmitting device conducts laser verification of the ground surface a maximum of 150,000 times per second (*maximum of 830,000 times for fixed wings), and the 3D coordinate results are obtained through post-processing. Thereafter, through a further process known as filtering, ground surface data is obtained from these results.
(Please refer to the page on DSM filtering for more details on filtering.)
When acquiring data, the characteristics differ depending on the aircraft (platform) used.
Characteristics of Surveying Using Fixed Wing Aircraft (Cessna for PASCO)
- Flight speed is relatively higher than that for rotating wing aircraft (helicopter), and the continuous flight time per flight is also long. As such, it is suitable for use in the surveying of a large surface area.
- In proportion to the higher speeds, the density of point clouds for each course tends to become rougher as compared to that for rotating wings. (Typically, about from 1 to 2 m)
- A higher level of aircraft posture stability and straightness of flight can be attained.
Characteristics of Surveying Using Rotating Wing Aircraft
- Flight speed is relatively lower than that for fixed wing aircraft, and the continuous flight time per flight is short. As such, it is used in the surveying of small surface areas.
- In proportion to the lower speeds, the density of surveying points for each course tends to become closer as compared to that for fixed wings. (Typically, about 0.5 m)
- Mobility is high, and surveying along terrain such as low altitudes and mountainous regions is possible. As such, it is easy to carry out surveying regardless of the local weather conditions.
With regard to applications, the results are presented and used in the following ways.
- Color map: A method that divides elevation values continuously based on terrain elevation data, and presents each category in a different color.
- Shaded map: A method that arbitrarily establishes the direction of the light source (sun) position and altitude for terrain elevation data, in order to facilitate understanding (in particular) of the terrain relief.
- Color shaded map: A terrain representation that synthesizes color maps and shaded maps. It is thus able to complement the flaws of each representation method when they are used on their own.
- Bird eyes map: A method that presents terrain elevation data in image of a bird's eye view from an arbitrary point in the sky. By continuously moving the perspective, this representation method can also be used for simulations on the computer.