Can the laser-scanning detect dampness ?

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mzhoum
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Can the laser-scanning detect dampness ?

Post by mzhoum » Fri Apr 18, 2014 1:09 am

We are looking for technology or software of point-cloud data processing and detect dampness of tunnel walls.
Is it feasible ? When we use scanner to scan the tunnel space, in addition to analyzing the space information, can we also get knowledge of the wall dampness, water leakage ? Please advice.
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Re: Can the laser-scanning detect dampness ?

Post by jedfrechette » Fri Apr 18, 2014 4:05 am

The near IR lasers that most systems use are pretty strongly absorbed by water so it usually is pretty easy to identify damp areas based on the recorded intensity values. Damp areas will typically produce lower intensity reflections than adjacent dry areas. Although making a qualitative visual distinction between damp and dry is pretty easy it might be a little more difficult to turn that difference in to a quantitative number, if that's what you need.
Jed

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Re: Can the laser-scanning detect dampness ?

Post by topa3d » Fri Apr 18, 2014 4:55 am

There are a few ways of visualizing whether water is present in a set of scan data. Researchers have used algorithms to detect water in lidar data with "fuzzy logic" - which shows a degree of separation in waveform from surfaces relative to water bodies (see:
2011_Schmidt_et_al_Hannover_Workshop-WaterDetection.pdf
) Because water scatters the laser and doesn't provide consistent returns, what is usually visualized is a lot of 'noise' or 'fuzzy' points around the water body.

Here are a couple of scans using a FARO Focus3D terrestrial scanner (appropriate for tunnel scanning).
Water droplets.JPG
This first scan is set to 'intensity greyscale' in FARO Scene 5.2, planar view. Along the beam, water droplets are visible.
Water droplets-intensity.JPG
Viewing this same scan in Bentley Pointools with 'soft hue intensity' we can see the bright yellow where the droplets are. Water does return a different intensity value. Although, this particular view is not enough for us to accurately detect water and requires looking for other signs such as missing data or distortions.
Floor covered in water.JPG
This floor is covered in about a cm of water which is not readily visible in this greyscale image. You can however see reflections on the floor next to objects such as the power cord.
Missing data.JPG
In this intensity image of the scans, it is clear where there is missing data on the floor. It appears sort of 'torn out' which is a combination of noise and no laser returns. You will see this noise on the opposite side of sealed surfaces. For example, a floor (or tunnel wall) is concrete, yet when visualized in the 3D scan, one would see points on the opposite site of this non-penetrable surface.

You may also see distortion with significant object submersion as shown below - although this was in a standing body of water which would not be the same as a wall surface.
Distortion.JPG
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Re: Can the laser-scanning detect dampness ?

Post by topa3d » Fri Apr 18, 2014 4:56 am

Here is another paper on the subject that speaks to missing lidar data in mapping water bodies. The workflow here is to 3D mesh the tunnel for example using something like Geomagic, Polyworks or the less expensive Leios (FARO Scene can accomplish limited meshing as well). You can map the water wherever the mesh leaves holes, assuming you have full scan coverage of the subject.
eogc_steuer_schaeffler_gross_standing_water.pdf
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Re: Can the laser-scanning detect dampness ?

Post by Phill » Fri Apr 18, 2014 10:28 am

Michael

All the above is true, but the problem you might run into is that as well as intensity return changing for dampness it also gets worse (lower) the further from the scanner you get, so picking an intensity number that you decide is damp may give poor results. Profiling in the tunnel in this case might be more appropriate, as if you run it down the centre the distances and intensity return should be more consistent. LIDAR has the advantage of being a long way from the subject and a fairly consistent distance, as well as using above mentioned profiling technique

Cheers Phill

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Re: Can the laser-scanning detect dampness ?

Post by hypsometric » Fri Apr 18, 2014 5:47 pm

Z+F lasers seem to have better contrast ratios for detecting potential moisture... but I havent worked with natural formation data...
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Re: Can the laser-scanning detect dampness ?

Post by lf2e10 » Sat Apr 19, 2014 9:58 pm

It is possible. You may have to calibrate the intensity data for distance and angle of incidence, depending on the survey topology used.

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Re: Can the laser-scanning detect dampness ?

Post by mzhoum » Sun Apr 20, 2014 8:57 am

Thank you all guys for the messages.
When we scan inside tunnel we experienced difficulty in determining dampness by intensity only. Issue is, the intensity may be reflected as the same degree but from different objects of dirty areas close to damp areas.
In all your feedback, I would like to discuss one by one with you. This mail can I seek ifze10 further advice about information "calibrate intensity data for distance and angle of incidence"? Can you explain more about it ? Thanks.
I
Michael Zhou, Professor
College of Urban Railway Transportation
Shanghai Univ. of Engineering Scence
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Re: Can the laser-scanning detect dampness ?

Post by lf2e10 » Sun Apr 20, 2014 10:10 am

Intensity reflects power density of returned signals, which can be affected by parameters such as angle of incidence. As a result, the intensity for the same material can be different. You can do a control experiment for the object you interested (i.e. tunnel walls) to see how intensity varies with these parameters and then to use the results for calibration.
Depending on the characteristics of the damp areas, you may also consider the photogrammetry technique.

Hope this helps.

Lei

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Re: Can the laser-scanning detect dampness ?

Post by jcoco3 » Sun Apr 20, 2014 4:50 pm

Hello Michael,

From what I have read here, I am getting the idea that integration of thermal imaging into you scans may help you distinguish those damp areas with the degree of accuracy you are pursuing. I know it is not as simple as just analyzing the intensity of the scans, but with a little manual tuning you should be able to detect the surface moisture and any areas that have become saturated beyond the surface. If the moisture temperature is equalized with the tunnel walls, then you may have to introduce some temperature change, which could be accomplished by shutting down ventilation for a period of time then resuming ventilation prior to imaging or simply adding a heat supply to the current ventilation system. I suspect that you will not have these problems due to the fact that the moisture may be evaporating which should be enough temperature change to be detectible by most thermal cameras.

I cannot provide much information in terms of how to setup you hardware because it may vary dramatically based on your needs. Recalling some previous post of yours, I believe you may be using helical scanning and I do not have much experience with that technique. I have some experience with static thermal scans. At SPAR last week I saw an impressive project Dr. Avideh Zakhor is working on that used a small robot equipped with laser scanners and calibrated thermal cameras, that could produce a thermal point cloud for an entire building. Zoller+Fröhlich also demoed a prototype thermal imaging accessory for the Z+F 5010c that was also quite impressive. It is unfortunate that these systems are still in their early stages, but you may be able to contact them to see when they will become commercially available.

Please excuse my lack of knowledge with respect to the tunnel scanning and mining, I don't have much experience in those areas, and what I have suggested may not be feasible for unknown reasons.

Hope this helps :)

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