Drone Lidar Components Present Data Quality Challenges

The use of drone LiDAR requires significant training and expertise especially when using inexpensive systems.

Riegl drone LiDAR flying over Treasure Island, California.

Riegl LiDAR flying over Treasure Island, California. Provided by Jamie Young- PrecisionHawk

(Editor Note – This is a cautionary tale told in the author’s words about the perils of self-proclaimed drone lidar experts.)

Training is Needed

There are a lot of people with drones who are collecting aerial imagery and becoming self-proclaimed mapping professionals in the process, but in fact they have little, or no experience. These individuals then make the next step to drone LiDAR which is much less forgiving then imagery because the systems are much more sophisticated and require a deeper understanding of the technology.

This is a similar phenomenon to what occurred when manned LiDAR became prevalent in the mapping profession. Currently, it seems that everyone is buying a drone LiDAR system which is presenting consumers of LiDAR data with a number of difficult problems. Only making matters worse is the fact that many of these LiDAR sensors are made with less expensive components which also affects the quality of the data.

Recently, I had a discussion with a combatant, LiDAR “Genius.” Turns out he had little experience with the technology yet insisted that he knew much more about the subject. He was downright militant with me explaining that he was going to take a M600 DJI drone with its GPS and IMU components, attach a Velodyne laser and obtain centimeter accuracy. I did not agree.

The takeaway from this conversation is that the lack of understanding of LiDAR technology in the drone world is becoming alarming. LiDAR has been mainstream in the professional mapping profession for over 15 years having become commercially viable as a mapping technology roughly 22 years ago when the positional systems needed to geo-reference the laser were integrated with the required accuracy.

LiDAR representation by Echo using a Riegl MiniVUX -1UAV.

LiDAR representation by Echo using a Riegl MiniVUX -1UAV. Provided by Jill Wrenn -PrecisionHawk

Positional Accuracy Challenges

The positional system is the GPS and IMU components of the LiDAR system and they are greatest source of positional error in the LiDAR data. This is more pronounced with drone LiDAR systems because the IMUs are much less expensive which causes greater error (drift) as it relates to the accuracy of the data. Luckily, this can be somewhat offset by the flying altitude of these sensors. It should be cautioned that this doesn’t mean that careful planning is not required when using these systems.

Positional systems require smooth and continuous transition in their movement, so the multi-rotor, copter systems are not conducive to this type of movement. It is imperative to get the best positional system for these sensors as a result of this. A DJI M600 navigation and location system is less than adequate for cm positional and locational data. I have never known high accuracy map data to come from systems that can only provide a location within 4 meters and attitude information within a few degrees, much less if the attitude information is even recorded properly.

Drone LiDAR surface model and points represented by Echo of Mounds in a LiDAR data set. Provided by Jill Wrenn – PrecisionHawk

LiDAR surface model and points represented by echo of mounds in a LiDAR data set. Provided by Jill Wrenn – PrecisionHawk

To further complicate the situation, the laser technology used for most drone LiDAR are marginal at best and yield less than favorable results in most cases. Some of the issues that have been observed are the complete lack of understanding of how to operate a LiDAR sensor as it relates to alignment and initialization of the sensor. In most cases these sensor issues need to be more rigid with these less expensive positional and locational systems.

Drone Lidar from Riegl Performs

The lasers, with the exception of the Riegl drone LiDAR sensors, in most cases cannot achieve the desired results. The calibration of these systems is not completely understood as it relates to what the mapping professional expects. I have yet to see an intensity image even close to what is expected with the exception of the Riegl Drone LiDAR.

Drone Lidar image

Reflectance data from a Riegl MiniVUX-1UAV. Provided by Jamie Young – PrecisionHawk

It should be understood that all LiDAR is not created equal and just because someone has a LiDAR it doesn’t mean they can collect accurate LiDAR data. There are drone operators that collect LiDAR and there are LiDAR operators that use drones. It shouldn’t matter what platform LiDAR is operated from if the company understands the technology. Professionals will know how to get accurate LiDAR data from any platform.

In closing, it is imperative that you research drone LiDAR companies before choosing which company collects your LiDAR. With the right company drone LiDAR can provide a wealth of information at a cost effective price.

 

James Wilder Young

PrecisionHawk Director Data Services – LiDAR Services

www.precisionhawk.com

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