The era of drone laser surveying solutions has arrived.
With TDOT 3, which irradiates a green laser that is not easily absorbed by water, you can seamlessly visualize 3D topography below the water’s surface from the ground.
TDOT 3 provides a one-stop service from the execution of surveying by flight to the creation of 3D data deliverables.
It is a surveying solution tool that can be used to grasp not only the topography of mountainous areas, but also riverbeds, coastal areas, or the condition of devastated areas immediately after a heavy rainfall.
Integrated platform that realizes the concept of easy surveying for everyone
A laser scanner system is composed of many precise devices, and it is not easy to set each one of them in an optimal condition. In addition, without specialized knowledge, it takes a lot of effort to master the work procedures through repeated trial and error to achieve highly accurate output. It is no exaggeration to say that the complexity of use required of these operators is a barrier to the widespread adoption of drone laser surveying.
TDOT 3 provides a platform that allows anyone to maximize its performance. This platform includes, for example, the ability to perform pre- and post-survey calibration flights simultaneously with flight route input, or to automatically perform optimal trajectory analysis in combination with INS data immediately after a simple drag-and-drop operation. By using our platform, which incorporates our surveying service know-how, anyone can easily perform laser surveying with accurate 3D coordinates.
Irreplaceable light, green laser
Sunlight and fluorescent light are a mixture of various wavelengths, but lasers are made by extracting only certain wavelengths from these (monochromatic) and focusing them to a single point (directional). The characteristics of the laser depend on the wavelength of the light to be extracted. Typical drone laser surveying uses lasers in the near-infrared region (905 nm). While near-infrared lasers are inexpensive and easy to handle, they are easily absorbed by water and have low reflectance on black objects, so data on the ground surface may not be obtained depending on the condition of the ground as well as the topography below the water surface.
TDOT 3 GREEN overcomes this weakness of near-infrared lasers because it irradiates lasers in the green range (532 nm).
Of course, it can also perform the same surveying as a near-infrared laser, making it possible to perform both ground and underwater topographic surveying with a TDOT 3 GREEN.
* Underwater measurements depend on the clarity of the water.
* It is difficult to measure the bottom of the water when it is muddy with algae, mud, etc.
Green laser drone surveying with the TDOT 3 GREEN can be used not only to survey riverbeds and seafloors (theoretical depth of 13.5 m), but also to survey wet ground and slopes in devastated areas, or objects with black surfaces such as landfill or asphalt, which have been difficult to survey with conventional near-infrared lasers. The green laser is also effective in surveying objects that were difficult to survey with conventional near-infrared lasers. The green laser is expected to play an especially important role in the urgent survey and assessment of devastated areas for rapid restoration.
Suitable beam diameter for laser surveying
Most lasers for drones are adapted from car-mounted laser scanner modules known as Lidar, which are attracting attention for automated driving. As these laser modules are designed to locate nearby obstacles and people, the laser beam diameter is very wide, and the distance data is not designed for accuracy. The wide beam diameter also obscures the location of the laser beam, which compromises the accuracy of the data.
The TDOT 3 laser scanner is a module developed specifically for drone surveying. A module for surveying purposes should not be designed to detect surrounding objects, but to measure objects as far away as possible with high accuracy. TDOT 3’s laser beam has a range accuracy of a few millimeters rather than the centimeters required for automotive use, and its ability to extend only 15 cm in diameter (1.5mrad) at 100 m makes it suitable for capturing detailed topography from 150 m above the ground.
90°viewing angle suitable for drone laser surveying
The FOV (Field Of View) was the most important consideration in the design of TDOT 3. This viewing angle was chosen to be 90° for the following reasons.
Elevation accuracy is a requirement for drone laser surveying. While horizontal position accuracy is important, elevation accuracy is very important for the purpose of the data. TDOT 3 scans a restricted area directly under the drone’s body, as shown in Figure 1. The surveying accuracy of the elevation value is the accuracy of the GNSS added to the ranging accuracy of the laser. The further the scan angle is from the vertical, the greater the surveying accuracy of the posture at the time of laser irradiation will affect the accuracy of the elevation. Therefore, the scanning range of the laser beam, called FOV (Field Of View), is limited to the green line as shown in the figure, and we emphasize obtaining elevation values that are less affected by the surveying accuracy of the posture.
Data acquisition range
FOV affects the data acquisition range. Figure 2 shows an example of surveying a steep slope with an FOV of 45°, and Figure 3 shows the data acquisition range with an FOV of 90°. The narrower the FOV, the more difficult it becomes to survey the sides of steep cliffs. Figure 4 shows an example of river surveying. If the FOV is 90°, it is possible to fly next to a bridge to acquire data under the bridge. Thus, a feature of TDOT 3 is that it is designed with practical aspects in mind.
When surveying is conducted with data accuracy and acquisition range in consideration, it is possible to use one that scans 360° around the drone and extract only the area directly below the drone afterward. However, this laser module has a complicated mechanism that increases the weight. The laser point cloud density directly under the drone is the same as one that scans 360° around it, and the module weighs less if it scans as limited an area as possible.
Lightweight directly related to flight time, safety, and convenience
Drones fly with multiple propellers powered by batteries. Without a payload, a flight of several tens of minutes is possible, but the heavier the payload, the larger the drone becomes and the shorter the flight time. Drones that can only be flown for short periods of time consume batteries quickly, which is dangerous because it increases the risk of crashes due to dead batteries. In addition, the convenience of the drone cannot be fully utilized if the battery must be changed frequently on site.
A lightweight, compact laser scanner can be mounted on a small drone, allowing for longer flight times. The dangers associated with flying are greatly reduced, as there is no need to worry about running out of battery power when surveying large areas, and you can choose more convenient locations for takeoffs and landings.
Aiming for “drone surveying that anyone can use,” we developed and launched the “TDOT” drone laser system in 2013 to enable aerial laser surveying, which could only be done with manned airplanes, to be conducted with drones. It uses a near-infrared laser and has achieved a lightweight scanner weighing 1.8 kg. By introducing this know-how, we developed a green laser scanner system, TDOT GREEN, in 2017, which was considered difficult to reduce the weight of the system, and we started production 2019. Incorporating innovations such as fiber-optic modulation technology, it weighs only 2.7 kg. The lightweight technology, which is highly functional and minimized to the utmost limit, improves footwork in business operations.
Achieving Higher Surveying Performance
Accuracy of drone position and posture measurements
Built-in high-performance INS with improved data output rate
In laser surveying, the laser beam must be calculated tens of thousands of times per second to determine how long it takes for the laser beam to return. In this process, the position of the laser beam is measured by GNSS, but GNSS can only make several dozen measurements per second, which alone can cause a large error in the position of the object. It also causes a positional slippage equivalent to the error in the measurement of the laser beam irradiation angle multiplied by the distance to the object. In other words, the further away the object is, the less accurate the coordinates of the object can be determined due to small errors in the laser beam irradiation angle. Therefore, an accelerometer is used to capture the drone’s movement, and a gyro sensor is used to detect the drone’s posture, which changes from time to time. The combination of IMU (Inertial Measurement Unit) and GNSS is called INS (Inertial Navigation System), and by utilizing the advantages of each other, a highly accurate surveying system can be completed. TODT 3’s INS has the specifications to achieve laser surveying of several tens of thousands of laser beams per second while providing a laser survey of several tens of millimeters.
REAL TIME DATA DISPLAY
Scan data is displayed in real time
You can see the data during surveying in real time. For example, by displaying a cross-section of the object, it is possible to check in real time during flight the acquisition status of ground surface data under vegetation in areas where trees are flourishing, and the status of reaching the water bottom in water areas. This allows the operator to check on the spot whether the surveying is being carried out as planned, and thus allows for efficient surveying operations without rework.
*To browse cross-sectional data during surveying, the drone must be equipped with an image transmission device that can be connected to HDMI. In the case of the DJI Matrice 300RTK, it is possible to browse the data through the DJI SkyPort.