Should I Stay, or Should I Go?—Manned LIDAR versus Drone LIDAR
Written by Jamie Young   
Saturday, 23 December 2017

A 3.983Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

Manned LIDAR has been widely used for roughly 20 year and Drone LIDAR recently has become a new tool in the Geonerd toolbox but are you just using it because its cool? When is it a good time to use Drone LIDAR or should you continue to use manned LIDAR? Is Drone LIDAR better? When is Drone LIDAR better? Is Drone LIDAR cheaper? What can I do with Drone LIDAR that I can't do with manned LIDAR? All these questions are very good questions but just because it's a Drone and a Drone LIDAR doesn't mean it is a lesser product or should be less expensive or more expensive.

The comparison of Drone LIDAR versus Manned LIDAR should be discussed. The only real similarity is Manned LIDAR uses much more expensive components and yields similar results but there are distinct differences. The Drone Sensors are smaller, operate on smaller platforms and require a smaller wallet thus the intended project areas will be smaller. At some point to collect a project with a Drone becomes less efficient but the data density will be much greater. Drone LIDAR can also facilitate the collection of very accuracy dense data within a larger project collected with manned LIDAR.

The differences
The differences as they relate to the functionality and what the sensors can yield are obvious to the sensor operators but may not be as obvious to the end users. Basically, The Drone LIDAR operate at roughly 40 to 100m above ground. The Riegl Mini-Vux-UAV sensors are capable of operating at higher altitudes, but current FAA restrictions prevent the operation of Drones above 500 feet. The fixed wing manned LIDARs, depending on application operate at much higher altitudes and the average operating altitude is between 1000 to 2000m AGL. Please note that this doesn't include Geiger Mode LIDAR which operates at significantly higher attitudes and Helicopter LIDAR that operate at much lower altitudes then Fixed wing LIDARs. Exact altitudes can be deduced from providers that operate a certain type of sensor and platform. The point density for Drone LIDAR will range roughly between 50 PPM at the low end to 500 PPM at the high end and manned LIDAR ranges between 1 PPM to 150 PPM. Please note that these point density ranges are not written in stone and are rough estimates bases on general guidelines. The point density is a function of several flight characteristics such as LIDAR point repeatability and AOI characteristics, such as man-made, vegetation and relief characteristics. Honestly, any LIDAR sensor can be flown to get any point density, it just becomes impractical at some point. The stated accuracy in general for Drone LIDAR depending on the sensor and processing, will range between 1.5 cm ­ 9 cm RMSE and potentially the accuracy could be a little better depending on survey and process but realistically you can expect these stated accuracies economically. Manned LIDAR accuracy typically is between 2cm -10cm RMSE and this includes helicopter applications. The fixed wing sensor can typically achieve between 6 and 10cm RMSE economically. Helicopter sensors are between 2 to 6cm RMSE. Currently, Drone LIDAR project area size as it relates to being most economical would range between 6 to 10 square miles or smaller. Manned LIDAR Project traditionally ranged between 1 square miles to several thousand square miles. Typically, Drones LIDARs can collect between 15 to 40 linear miles a day depending on the system and Drone. Helicopters can do more but the points density is not as dense. This is a comparison similar, to the relationship of fixed wing LIDAR point density versus Helicopter LIDAR point density.

How to determine which should be used?
This is very hard to generalize, and each project should be carefully evaluated for what sensor approach should be used. This can be compounded by the characteristics of the sensors such as number of returns per pulse. This is important because current Drone LIDAR sensors range between 2 returns per pulse, up to 5 returns per plus, whereas Manned LIDAR can report several returns per pulse. Geiger and photon LIDAR sensors operate differently making this a non-issue.

Basically, the following questions should be asked to determine if Drone LIDAR or Manned LIDAR should be used. What is the size of the project being mapped? The general rule of thumb was answered above. How many areas do you want to map as they relate to the size of each area? Several extremely small areas would probably be best mapped with a Drone LIDAR. What features are you mapping? and How much detail do you want to get? Drone LIDAR (roughly 50 to 500 PPM) achieves significant detail. The algorithms that can be run on this level of detail definition can yield features, common to mobile mapping detail. The features such as individual walls, cars, trees, and other detail features can be extracted. Additionally, small scale routine LIDAR collections on changing natural features and man-made structures can be mapped with drone effectively and economically. Large projects with smaller areas requiring very dense collection within the large project potentially could be done with drone LIDAR to limit the cost as it relates to using another platform.

One developing Drone LIDAR technology is bathymetric LIDAR. This is an extremely exciting application because historically bathymetric LIDAR projects are much smaller than topographic LIDAR projects. Additionally, these projects are isolated to small water bodies and streams. The vegetation and terrain characteristics around water bodies and streams can be extremely challenging making Drone Bathymetric LIDAR, the best solution for this application. Additionally, weather conditions and atmospheric conditions around water present additional challenges for the Manned LIDAR approach makes the Drone approach more economical.

Cheaper LIDAR
Drone LIDAR can be less expensive then Manned LIDAR for small project areas and as stated the economic benefit of Drone LIDAR diminishes at some point based on the size of the project. The importance of understanding the meaning of less expensive means it is key to this discussion. Yes, it is less expensive to fly Drones for small projects as it relates to the basic product understanding of LIDAR data. There is a significant benefit of the Drone LIDAR technology, as it relates to the accuracy of the data and the much lower flying height of the platform and the significant increase of point density. Additionally, advances in Drone LIDAR technology, as it relates to flying height, limited to the airspace operating altitude will further reduce the cost of Drone LIDAR. Much like the increased repetition rates of manned systems, resulting from increased flying heights, the cost of manned LIDAR was reduced. The actual point density as it related to the actual specified point density is much greater than required with Drone LIDAR. Drones LIDAR will be collected at roughly a minimum 50 PPM at the highest possible flying height regardless of required specified point density.

In most case the collection of Drone LIDAR will be less expensive or in some cases equal to Manned LIDAR, but the entire project delivery and specification needs to be considered. In simple terms the more you get, the more it will cost. Given the resolution and definition of the Drone LIDAR data, there is more value in the data set based on that definition. Additionally, similar too manned LIDAR, there is a cost associated to what is extracted from the data, which can be much more information from Drone LIDAR.

What is needed and what technology should be used?
In several previous articles by this author it has been reiterated the need to understand what problems are to be solved and what solutions are required for a given application? Additionally, there are potential additional uses for the data as it relates to applications that were not realized previously by both the user and provider. Commonly, a given project collection and application results in the end user discovering additional uses for the data. The reason why this is usually recognized by the end user is because they usually have much more experience with their application. This is much more obvious during the initial evolution stages of an emerging technology such as Drone LIDAR. It is very important to understand that just because a given specialized LIDAR technology is being presented by a company that specializes in that given LIDAR technology, doesn't mean it is the best technology for a given application.

Drone LIDAR provides a valuable tool for solving problems and providing solution because of the increased point density, feature definition and improved accuracy that doesn't currently exist with manned sensors. Again, this is a welcomed addition to the Geonerd Toolbox and it has its place in the geospatial profession. The resulting decreased operation cost continues to provide less expensive solutions to professionals that would not otherwise be able to procure LIDAR data. This is especially prevalent in smaller project as it applies to both topographic LIDAR and Bathymetric LIDAR or a combination of both. Added value can also be recognized with the addition of other remoted sensed data such as RBG, Multispectral, Thermal and Hyperspectral data.

James Wilder Young (Jamie) CP, CMS-L, GISP is currently Director ­ LIDAR Services for PrecisionHawk, headquartered in Raleigh, North Carolina, the leader in providing innovative information data using drones. He is currently supporting all aspects of LIDAR technology as it relates to drone technology. His experience includes all aspects of LIDAR including sensor development, applications development, data acquisition, data processing and project management. He graduated from The University of Colorado.

A 3.983Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE