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This is an old revision of this page, as edited by 83.253.248.109 (talk) at 08:44, 22 April 2010 (italics and a minor link fix). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

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Aren't radio waves light, technically?

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 09:31, 28 June 2003 (UTC)[reply]
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...
— Preceding unsigned comment added by 217.158.106.44 (talk) 10:03, 28 June 2003 (UTC)[reply]
(A comment by 131.107.0.102, 10 November 2009, was moved down to More on the definition of light below, due to the age of the above discussion.)

Article name

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 there 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 should 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 — Preceding unsigned comment added by 66.159.192.247 (talk) 05:16, 28 April 2004 (UTC)[reply]

Mirror choice

Can anyone tell me what some of the pros & cons are of using a polygon mirror? — Preceding unsigned comment added by 209.247.234.99 (talk) 15:13, 13 April 2004 (UTC)[reply]

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, except it emits imaging too. — Daniel 01:34, 21 December 2005 (UTC)[reply]

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. — Preceding unsigned comment added by 142.167.179.232 (talk) 10:32, 20 March 2006 (UTC)[reply]

Cleanup

The style on this article is horrible[1]. 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)[reply]

That massive chunk[2] 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. — Preceding unsigned comment added by 142.167.179.232 (talk) 10:35, 20 March 2006 (UTC)[reply]
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 summarise what has been removed. Unless anybody argues against this I shall try and spend some time 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)[reply]
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[3] 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 as sensor for autonomous control of vehicles - a somewhat different type of instrumentation. Op. Deo 23:00, 22 March 2006 (UTC)[reply]

A resource

The following article by the National Institute of Standards and Technology would provide some good background information to help with a cleanup of this section. — Preceding unsigned comment added by Flyingpolarbear (talkcontribs) 19:33, 17 March 2006 (UTC)[reply]

Performance Analysis of Next-Generation LADAR ... (NISTIR 7117; 198 p. May 2004)

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).

LIDAR#Design

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 (talk) 21:25, 10 April 2006 (UTC)[reply]

A more general introduction, and more

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 parameters. 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 light-photon 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.
— Preceding unsigned comment added by 130.225.79.64 (talk) 14:18, 12 April 2006 (UTC)[reply]

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 compared to RADAR too, not just the advantages. Short wavelengths also imply more scattering, less range, for example. Tarchon (talk) 00:50, 18 April 2006 (UTC)[reply]

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? — Preceding unsigned comment added by 69.156.43.137 (talk) 04:53, 2 June 2006 (UTC)[reply]

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)[reply]

The picture of the laser

I'm somewhat sceptical of the picture of the laser...if the laser interacted with air particles, it would encounter too much interference and would never reach the intended target, so I believe someone has skilfully photoshopped the picture with a lightsabre-like beam – anyone? — Preceding unsigned comment added by 195.172.14.80 (talk) 09:14, 26 June 2006 (UTC)[reply]

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).
(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)[reply]
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)[reply]

Removed {{cleanup}} tag

The article[4] 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)[reply]

Lidar measurements and techniques

I think there should be a section listing the different techniques for measuring each parameter such as aerosol type and air temperature. — Preceding unsigned comment added by Cap.fwiffo (talkcontribs) 21:18, 20 August 2006 (UTC)[reply]

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)[reply]
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 (talkcontribs) 18:55, 29 December 2006 (UTC)[reply]

In fiction section?

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 (talk) 18:26, 24 December 2006 (UTC)[reply]

Hey y'all: I've reverted[5] a previous removal of KQED-TV (PBS) science story on LIDAR External links; did not get reply from User:JuJube after requesting clarification for removal. Craigrosa (talk) 18:13, 16 May 2007 (UTC)[reply]

WP:EL: No link should be added unless its inclusion is justified. Until there is consensus for its inclusion the link should not be reincluded. Femto 12:24, 2 June 2007 (UTC)[reply]

How about a link or mention somewhere of some of the leading commercial contenders eg:

I see there is already a link[6] from the Zephir disambiguation page to this lidar article. Other sources of information on these products at:

Davagh (talk) 16:00, 27 February 2009 (UTC)[reply]

Galion added by 91.135.13.220 (talk) 16:37, 25 January 2010 (UTC)[reply]

This page slows down my browser

This is the only Wikipedia page that has ever slowed down my browser. Is it because of the animated pictures? Running Mac OS X and Firefox. — Preceding unsigned comment added by 76.17.212.193 (talk) 00:51, 21 September 2009 (UTC)[reply]

More on the definition of light

(Comment moved down from Isn't radio waves light, technically? above, due to the age of that discussion. --83.253.248.109 (talk) 13:49, 20 April 2010 (UTC))[reply]

The article on light is ambiguous on this discussion ("In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not" ). It would seem most clear to simply edit the lede to remove "which is light that is not in the visible spectrum..." (the clause[7] is unnecessary and reads somewhat awkwardly anyway, I think). A reasonable alternative would be "which is electromagnetic radiation not in the visible spectrum," I think. Not that this is a huge issue, but the wording is odd enough to have caused me to click the discussion tab. ;) 131.107.0.102 (talk) 19:03, 10 November 2009 (UTC)[reply]

Is the term "laser radar" really misleading?

The sentence about calling "laser radar...misleading"[8] doesn't feel right. My logic is that LIDAR would in fact be a type of radar. Many of what we call radars utilize the microwave bit of the spectrum. Radar grew beyond its original acronym some time ago. Do even shorter wavelengths make a radar not? ~ Theparadigmshifter (talk) 06:45, 23 January 2010 (UTC)[reply]

"Laser radar" simply means: "like radar, but with laser light" (instead of radio waves).
I see the two most basic properties of a radar system as: 1) The basic working principle, which on a very general level is sending something out and detecting its reflection, and 2) The sending and detection of radio waves or microwaves. The first is shared by LIDAR, and the second just differs in which part of the electromagnetic spectrum that is used.
The only way I can see that one could be mislead by the term "laser radar", is if one thinks that the word radar in the phrase means that "laser radar" involves radio waves or microwaves. But one who knows that much about radar, most likely is able to figure out that the word laser in the term means that that part of the electromagnetic spectrum is used, rather than radio or micro waves as in radar.
More importantly:
To claim that something is misleading, you should either be able to show that someone has been mislead by it in any significant way, or, at the very least, show in some way that people are likely to be mislead by it.
And just in case you find someone who has managed to become mislead in some way by this term; is that of enough statistical significance or notable enough to deem the term "misleading" in the lead section (or anywhere else)?
In my opinion, the term "laser radar" is not misleading in any significant way. --83.253.248.109 (talk) 23:24, 21 April 2010 (UTC)[reply]
Bye the way, ever heard about "optical maser"? That's a "maser", which instead of emitting microwaves like a regular maser, emits radiation in or near the visible spectrum. It's also called a "laser". --83.253.248.109 (talk) 23:53, 21 April 2010 (UTC)[reply]