Talk:LIDAR
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Call me crazy, but aren't radio waves technically light as well? Thus it's hard to say that LIDAR uses light rather than radio waves... --Dante Alighieri 09:19 28 Jun 2003 (UTC)
Light and radio waves are both distinct forms of electromagnetic radiation. I don't think the definitions of light and radio waves overlap. The wavelength range of light is about 400 to 800 nm, while the range of radio waves is about 0.1 m to infinity. These ranges do not overlap. See Electromagnetic spectrum. -- Heron
Well, I'm not talking about visible light, but light as a generic term... used to refer to the entire electro-magnetic spectrum. If light refers only to visible light, then it seems rather redundant to call it visible light. ;) --Dante Alighieri 09:45 28 Jun 2003 (UTC)
Infra-red and ultra-violet are generally thought of as light too. Generally "light" is used to refer to anything between the far infra-red to the extreme ultra-violet. Terahertz radiation represents the grey area between "light" and radio at the low end, and EUV starts to blend into "soft" X-rays at the high end.
So it's:
- Radio
- ELF, VLF
- ...
- UHF
- Microwaves
- Terahertz rays (grey area)
- Light
- Far IR
- Near IR
- Visible spectrum
- "Red, orange, yellow, green, blue, indigo, violet"
- Ultra-violet
- Extreme ultraviolet (grey area)
- X-rays
- Gamma rays
- etc...
-- Anon.
Is LADAR the correct term here - or should it be LIDAR? Perhaps with a sub heading for Ladar.
- Ladar also seems to have a lot of eye surgery references as ther is a tradenamed procedure that begins with Ladar.
- Also see
Ladar which cross references to Lidar, as a more general term.
- A google search for Ladar gives 9,160 entries, while a google search for Lidar gives 296,000.
Lidar is linked to Ladar in Wikipedia. I think it should be the other way around, or there be two entries. Also should these terms be capitalised? They are spelt as Ladar and Lidar in many internet entries.
- Any thoughts? kiwiinapanic 09:59, 17 Dec 2003 (UTC)
- I'm with you on this. I originally created this as an offshoot of RADAR and have since learned that it's much more common to refer to it as LIDAR. Feel free to move it! Maury 13:19, 17 Dec 2003 (UTC)
- Page moved from LADAR to LIDAR. kiwiinapanic 11:37, 31 Dec 2003 (UTC)
Lidar is the more general term. The distinction between lidar and ladar depends more on the nature of the target. Traditionally lidar has been used to refer to diffuse targets (eg atmospheric aerosols) while ladar has been used to refer to hard (ie solid) targets. In the early 90s there was a letter submitted to Photonics Spectra (IIRC) that discussed the subtleties of this issue. Personally I tend to use the term laser remote sensing these days as not all of the instruments I develop in my professional life provide range information and lidar is therefore a subset of laser remote sensing. There are a number of implicit assumptions built into the information currently conveyed on the page that are not always correct. I will think about how to correct these with minimal editing changes but do not have time at the moment. --Gary Spiers - www.lidar.com 06:15 28 Apr 2004 (UTC)
Contents |
[edit] Mirror Choice
can anyone tell me what some of the pros & cons are of using a polygon mirror?
[edit] Acronym
LADAR stands for LASER Detection and Ranging. LASER stands for Light Amplification by Stimulated Emission of Radiation. If you string the whole thing together, you get "Light Amplification by Stimulated Emission of Radiation, Detection, and Ranging." How do you emit detection and ranging? Same thing goes for LIDAR, exept it emits imaging too. — Daniel 01:34, 21 December 2005 (UTC)
LASER in the name simply refers to the device which emits a coherent beam of light. LIDAR is simply Detection, Ranging and Imaging through the use of a scanning laser. Trying to work the LASER acronym open inside the LIDAR acronym is unnecessary.
-anon. user
[edit] Cleanup
The style on this article is horrible. It's poorly formatted and many parts sound very informal. I'm gonna mark it for cleanup. 69.161.13.68 22:36, 13 March 2006 (UTC)
That massive chunk added by Mcgowan30 is just... a mess, and seems to be entirely focused on laser-based speed traps, but as an anon I'm hesitant to simply wipe it.
- I just took my eye off this article for a few weeks and look what has happened. I agree entirely with the comment just above. It will need some work to tidy up, and it was never very good to start with. I would be prepared to have a go in producing a balanced shorter article. The first thing I would do is to move all the addition on the laser speed measurer to another article (presumably new - I'll have to check there is not already one covering this). Then I would write a paragraph to sumarise what has been removed. Unless anybody argues against this I shall try and spend sometime at the weekend on this. That is of course if no one else has had a go at a cleanup in the mean time. Op. Deo 22:39, 22 March 2006 (UTC)
-
- Back again! having nosed around a little it seems that the part added by Mcgowan30 is straight off a motorbiker's description of laser speed guns. It is therefore a copy violation unless the webpage author has released it for use in WP. I will therefore delete the whole of it for now. I will come back at the weekend and try and write a short paragraph using the deleted material. The reference given below also contains useful background on the development of lidar a sensor for automonous control of vehicles - a somewhat different type of instrumentation. Op. Deo 23:00, 22 March 2006 (UTC)
[edit] Resource
The following article by the National Institude of Standards and Technology would provide some good background information to help with a cleanup of this section:
http://www.bfrl.nist.gov/bfrlnews/NISTIR_7117_Final_Complete.pdf
[edit] Laser sources
"600-800 nm lasers are most common for non-scientific applications. They are inexpensive and can be found with sufficient power but they are not eye-safe. Eye-safety is often a requirement for military applications. 1550 nm lasers are eye-safe but not common and are difficult to get with good power output. Laser settings include the laser repetition rate (which controls the data collection speed) and pulse length (which sets the range resolution)."
1550s aren't all that rare nowadays. I'm not really sure I buy the rep rate comment either. Maybe that's true for power, but if you needed a lot of power you'd be using a YAG anyway - right? - not a 600-800 diode. 600-800 isn't a very good range limit spec either if this is supposed to imply "conventional III-V edge-emitting diode" - 904 nm LIDARs are common as dirt. Is this section from an outdated source perhaps? Tarchon 21:25, 10 April 2006 (UTC)
[edit] More general introduction?
All kinds of systems and applications use the term LIDAR. Not all LIDARs are based on lasers or pulses. And the distance measurement is only one of the measured paramters. I suggest the following more general introduction.
LIDAR (LIght Detection and Ranging or Laser Imaging Detection and Ranging) is a technology for remote sensing. In many ways it is similar to radar, but based on light instead of radio waves.
LIDAR technology has applications in several fields. Among other it is used for traffic surveillance, air pollution studies, remote spectroscopy and for precise mapping and distance measurements.
Other common terminology for LIDAR is LADAR or laser radar.
I am also working on a short general principle section. Which could be followed by the following applications section suggestion:
The primary difference between LIDAR and radar is that LIDAR uses much shorter wavelengths of the electromagnetic spectrum, typically in the ultraviolet, visible, or near infrared.
As the intensity of electromagnetic scattering from a particle depends on the wavelength light is sensitive to small particles like aerosols. LIDAR is therefore used to remotely measure airborne pollution, cloud formation and even clear atmosphere wind. LIDAR systems taking advantage of this phenomenon are DIAL and DWL.
An object needs to produce a dielectric discontinuity in order to reflect the transmitted wave. At radar (microwave or radio) frequencies a metallic object produces a significant reflection. However non-metallic objects, such as rain and rocks produce weaker reflections and some materials may produce no detectable reflection at all, meaning some objects or features are effectively invisible at radar frequencies.
A lightphoton also has a more energetic energy quantum then a radio-wave photon and will interact with electrons and vibrational states of atoms and molecules. LIDAR is therefore used for remote spectroscopy of trace gases in the atmosphere, for example ozone, methane etc. For the same reasons it is used for measurements of chlorophyll for biomass studies. RAMAN LIDAR and DIAL.
The shorter wavelength also implies that very narrow beams can be produced, typically with a divergence of less than a mrad. This characteristic allows distance and feature mapping with very high resolution compared with radar and that target clutter can be avoided. LIDAR are therefore used for missile guidance and traffic surveillance.
and finally a more detailed principle description of the different subsections.
- I agree about generalizing it. Restricting LIDAR to pulsed laser techniques is just incorrect. It might be better to describe that as the way LIDAR is usually done. I'm never quite sure where LIDAR ends and profiling begins though. I'd mention the disadvantages compareed to RADAR too, not just the advantages. Short wavelengths also imply more scattering, less range, for example. Tarchon 00:50, 18 April 2006 (UTC)
[edit] LIDAR and RADAR interfering with one another
Does anybody know if lidar and radar were fixed on the same target from roughly the same place if they could mess with each other? —The preceding unsigned comment was added by 69.156.43.137 (talk • contribs) .
- I can assure you that lidar (visible or near infrared light) and radar (microvawe range) use wavelengths differing by several orders of magnitude. Therefore no interference is possible. If it were, you would actually see microwave radiation interfering with light inside a microwave oven. It does not happen and intensity of both form of electromagnetic radiation in an oven are much higher than what a radar or lidar use to illuminate a target. Friendly Neighbour 05:49, 2 June 2006 (UTC)
I'm somewhat sceptical of the picture of the laser...if the laser interacted with air particles, it would encounter too much interfernce and would never reach the intended target, so i believe someone has skillfully photoshopped the picture with a lightsabre-like beam anyone? —The preceding unsigned comment was added by 195.172.14.80 (talk • contribs) .
- The bright laser beam is clearly impossible. First of all, it would break US safety rules on how intense beam you can send into the atmosphere (not to blind airplane pilots). It's either a fake (photoshop job) or a dual exposition photo (short daylight exposition overlayed on a long nighttime photo of the beam). Friendly Neighbour 10:09, 26 June 2006 (UTC)
- (continued) Yes, it's a dual exposition photo. You can see how the stars moved during the nighttime exposition in the original large photo while the clouds in the lower left corner (photographed in daylight) do not move (are not blurred). Friendly Neighbour 10:16, 26 June 2006 (UTC)
-
- You are mistaken in general, and although I have no way of knowing if the particular image on the page is authentic or not, I have no reason to believe it is fake. Atmospheric research lidars in visible wavelengths are easily visible by the naked eye during nighttime, and have an appearance exactly like in this photo, except that the ones I've seen myself have all been green. To ensure aviation safety, powerful lidars are marked on aviators' maps, and there are exclusion zones around them. Operators also use protective goggles which block the wavelength of the lidar.
- As for your claim that this is a dual exposure, I suggest you take a look at many more nighttime long-exposure photos before you make strong claims of forgery. In what way do you suggest that it was necessary to make a daytime exposure to create this scene? --Togr 07:37, 22 July 2007 (UTC)
[edit] Removed cleanup tag
The article seems well organized and well written, although a bit technically confusing with all the terms you use. You need to add a reference section for citations sourcing your information. KarenAnn 15:21, 6 July 2006 (UTC)
[edit] Lidar measurements and techniques
I think there should be a section listing the different techniques for measureing each parameter such as airosol type and air temperature. —The preceding unsigned comment was added by Cap.fwiffo (talk • contribs) .
- You are free to start one. However the techniques for different aerosol types are identical; the only thing that differs them is the backscattering coefficient for a given particle size / wavelength combination. It's the trace gases that need a different approach. Friendly Neighbour 21:24, 20 August 2006 (UTC)
I'm afraid Friendly Neighbour misspoke. Even for aerosols, there are a number of different measurement techniques that are commonly used. Simple backscatter lidar (e.g., the spaceborne lidars GLAS and CALIPSO), Raman lidar, and high spectral resolution lidar (HSRL) are all commonly used to measure both cloud and aerosol properties. For trace gases, differential absorption lidar (DIAL) is the tool of choice...but even DIAL can be (and is) used to make aerosol measurements. Xavier onnasis 18:55, 29 December 2006 (UTC)
[edit] In fiction
LIDAR may be used in science fiction as an alternative to RADAR. I'd add a section but I'm not sure it meets notability requirements, as the only thing I know of for sure that uses it is Space: Above and Beyond. 69.81.123.154 18:26, 24 December 2006 (UTC)
[edit] restored link to KQED
Hey y'all: I've reverted a previous removal of KQED-TV (PBS) science story on LIDAR external link; did not get reply from member JuJube after requesting clarification for removal.
Craigrosa 18:13, 16 May 2007 (UTC)
