Mobile vs. Airborne LiDAR

I had an interesting conversation today with a person that works for a department of transportation in the US. They did an extensive comparison of static, mobile and airborne LiDAR against traditional survey. I am hoping to get the link to the study.

They had some issues with the mobile scanning technology, but have recently committed to doing 6 projects with airborne LiDAR. I asked if this was because of the bad experience with mobile. The answer was no. The reason was the swath width. Mobile could not be used due to wide medians and very steep side slopes – good points, and ones that will be very hard to overcome.

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12 Responses to Mobile vs. Airborne LiDAR

  1. conor says:

    That study would be very interesting, if you can get it please post the link, thanks Gene!

  2. Bill Gutelius says:

    Interesting. I think that much of the marketing language from the mobile system vendors paints a too-rosy picture of the amount and completeness of swath coverage an operator can obtain.

    There are many issues with driving a mobile scanning system down a corridor – not the least of which are the adjacent obstructions. The reality is that a blend of approaches (airborne AND ground mobile, with static too perhaps) may likely be required to sufficiently and adequately acquire corridor data. As is often said, there are no silver bullets (to scanning solutions).

    I think that this is where a really good, extensively-experienced service provider is valueable: they are able to determine the right “horses for courses” so to speak.

    Can’t wait to see the link to the report.

  3. Lewis Graham says:

    I would definitely agree with Bill’s comments. Except for very specialized applications, a scanning serivce provider would have access to and consider all technologies on a project-by-project basis. For example, if the project is bridge clearance, then the project will have to involve mobile. If the project is Right of Way, it will nearly always have to involve airborne and so forth. It is really distressing to see the debates of one technology versus another. Most of the technologies are complementary.

  4. If the proper controls are in place wide medians and steep side slopes can be easily overcome by making multiple passes which can then be meshed as the collected data is processed. Though on extremely large projects a combination would be the key, on average or smaller projects intimate detail as well as the ability pass under bridges, stop and collect data under bridges for design, etc., etc, easily outweighs the extra time spent making multiple passes. The key is a better understanding of the data collection and transformation process.

  5. Jim Peterson says:

    Great point Bill, “no silver bullet” and “right horses for the courses”. I like the idea of the blend of air, mobile, and static as well. I would even include the possibility that traditional photogrammetry may well be part of the blend. I would also like to point out that many of the medians and side slopes can be obtained by driving on the shoulder or safety zone. You still have the grass and weeds issue where bare earth becomes a problem. However, if a client only needs the edge of pavement to edge of pavement, the accuracy is hard to beat. But, herin lies another issue. Many providers do NOT understand the accuracy of mobile lidar. It isn’t just about meeting some mapping standard. It is KNOWING where you might have less than accurate results. Many approaches are more of a shotgun approach rather than a rifle on the poor accuracy locations. Much data has been turned in thature has MUCH less accurate data than their accuracy reports indicate. I also know that data has been provided that coudl be much MORE accurate that represented. Mobile Mapping at the “engineer and/or survey grade accuracy” is a COMPLETE workflow approach based on the application required. Many providers are treating that as a “one size fits all” approach. Some service providers have left a “bad taste” in a few DOT’s mouth. It is a shame, but it will seperate those who provide a professional service with great care… and most of all…. indicate what it DOESN’T DO.

  6. Brent Gelhar says:

    Speaking from the perspective of an airborne, ground based and mobile lidar system developer and manufacturer, it is always a challenge to ensure that these new technologies are not being oversold. Unfortunately clients are often looking for the proverbial “silver bullet” and it is difficult to manage expectations of the buyer. Remember that people typically only hear what they want to listen to and ignore the rest. I have personally experienced many occasions where clients have been told the limitations and are cautioned against overly optimistic expectations, even to the point of being told not to purchase, but ultimately end up somewhat disappointed. Objectivity, caution, consultation and patience in making the correct tool choice for the job are always key. As in the latin saying, Caveat emptor….let the buyer beware, even of themselves!

  7. Please post this study. I am very interested.

  8. With any technology or application thereof, the most crucial elements are knowing the limitations and how to compensate for those limitations. Whether its obstructions, resolution or accuracy, each technology presents there own challenges to address. We are working with remotely sensed data. It has advantages and disadvantages with respect to traditional surveying, not the least of which is familiarity by the client. Knowing how and when to apply a given technology is important to the success of any project.

    I hope you’re able to distribute the study, Gene. I think it will be a valuable educational tool for us all.

  9. One issue I’ve yet to see investigated is what the presence of low vegetation does to identifying the ground surface. Both technologies are challenged by this but I have not seen evidence to prove which one copes with this issue more effectively. Aerial LiDAR requires some discrimination distance (even with wave-form, there has to be some) and mobile scanners are typically going to see the vegetation from an oblique angle meaning the signal must travel further through the grass in a linear distance to the ground surface – but typically there are vastly more observations…

  10. Eric Andelin says:

    Just like aerial and tripod based LiDAR there are limitations. I think it’s a little sensationalistic to suggest that the US DOT is blessing Aerial over Mobile. While ROW to ROW acquisition is difficult to acquire with mobile LiDAR where there are large medians, in many cases there is an existing data set that is perfectly acceptable for the non paved surfaces within a ROW. While DOT’s may place a value on what’s within the ROW based on a given project, many of their projects are concerned with the road surface only. Or the assets along and above the road, or guardrails, or visibilty coming on and off the highway. All things where Mobile LiDAR may be the better platform for acquisition. For example Woolpert just completed what is currently the largest Mobile Mapping project for TxDOT. I-30 from the Trinity River to Just West of Arlington. An existing Auto Correlated Surface (ACS) extending out beyond the ROW was merged with a higher accuracy Mobile LiDAR surface collected from EP to EP. The result, a high accuracy data set where accuracy was needed, and savings from re-using existing data where the existing surface was perfectly suitable. Another deliverable included “Street View” style imagery not attainable from an aerial platform. ON another project near Washington DC, our mobile system acquired a 40 plus mile section of interstate with large medians separating North and South bound lanes. Aerial LiDAR was also acquired and merged at points where the median was to large or had dense vegetation. In another area Tripod based LiDAR was used to collect extremely high detailed data under some bridge spans. All forms of LiDAR were used and merged to create the clients desired deliverable. One acquisition platform is not the panacea, each meets a need that the other may not feasibly accomplish. It is the service providers and the communities responsibility to educate the client on the limitations and advantages of each.

  11. Conor says:

    did this report ever get published? Im trying to remember if you ever posted it, but im afraid i cant.

  12. ulises cano says:

    “……..There are many issues with driving a mobile scanning system down a corridor – …..”.
    I´m also agree. Anyway , combination between mobile scanner and accurate airborne data set´s must be possible if the Master points cloud is from ALS. But a special automatic adjustment package is necessary. Is such tool existing in the market ?

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