Talk:Radar cross section
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Removal of statement about downtime
[edit]- This conversation was moved from my talk page to here. =Axlq
You removed my sentence regarding outdoor and indoor test ranges from the article "Radar Cross Section" saying it was unsourced and untrue statement. But I read it in the very first reference - Knott and Shaeffer that outdoor test ranges typically suffer a 35% downtime. Also indoor test ranges suffer the limitation of the size of test object. Is it wrong? User:Warlord88 13:27, 21 March 2007 (UTC)
- I removed the sentence for two reasons: I couldn't find the citation associated with it (you did), and it contained a false statement that they cannot be used in "unfavorable" weather (regardless of what the reference says, I know from professional experience that such a statement is false). Removal of the part about 35% downtime was unintentional. I believe I have the Knott/Shaeffer reference at work - would you mind telling me where you found the statement? I have no problem with restoring the sentence. =Axlq 02:50, 25 March 2007 (UTC)
- The part regarding downtime is in the very first chapter of Knott and Shaeffer on page 13, paragraph 3. I also read this part in lecture notes of Robert W. Borek which I stumbled upon while browsing. I reproduce the part below:
- Indoor ranges suffer limitations in the size of the targets that can be measured, whereas outdoor ranges suffer down time problems due to weather conditions. Although the indoor ranges offer protection against the weather and intruders, outdoor ranges can often measure full-scale targets under far-field conditions.
- Probably the single most important disadvantage of outdoor measurements is the long-term effects of weather. Measurements cannot be made in the rain because of moisture collection on targets and target support columns and the backscatter from raindrops in the measurement zone. When rain is not a problem the wind usually is.
- You have Knott/Shaeffer at work and you have professional experience in test ranges? What do you do? I am doing my undergraduate seminar on 'Radar Cross Section' and hence am interested in the topic. User:Warlord88 07:35, 26 March 2007 (UTC)
- Ah. What you quoted above is quite different from saying that outdoor ranges "cannot be used in unfavorable weather." Yes, they suffer downtime due to weather because most measurements require good conditions, but they are used in unfavorable weather, if the purpose of the measurement is to include the effects of weather. Again, I have no problem restoring your edit. My objection really focused on the phrase "cannot be used".
- Yes, I have professional experience in test ranges. I don't have the same job anymore, but in the past I planned and participated in radar test events for Navy ships. Those outdoor ranges usually consist of a radar mounted on shore, tracking the ship a few miles away while turns in slow circles. Because there are no support columns fixing the target in place, you must contend with variable distance to target. Having different weather conditions was valuable for characterizing the distribution of RCS as a function of weather or sea state. Another version of a Navy outdoor range involves a helicopter flying around the target, with the measurement radar in the helicopter. Either version requires a precise transponder to be mounted on the target so that you can perform downrange distance corrections in post-processing later. =Axlq 15:05, 30 March 2007 (UTC)
Spurious definition of RCS
[edit]This statement (in the first paragraph) is spurious:
"The RCS of a target object is equal to the cross-sectional area of a perfectly conducting sphere that would produce the same magnitude of reflection as that observed from the target object."
It is only correct (or, at least, approximately so) in the high-ka limit. A clear way to demonstrate its invalidity is to ask "What is the RCS of a perfectly conducting sphere?" By the definition given above, it must be, at all frequencies/wavelengths, \pi a^2, the cross-sectional area of the sphere. But, of course, in the resonance region the RCS of a sphere is not constant; it wobbles about the high-ka limit. And in the low-ka limit the RCS falls precipitously.
The correct definition for RCS is stated later in the article: \sigma = 4\pi P_backscatter / P_intercepted
- You are correct. I made some changes to the article to clarify that the RCS is the same as a sphere only when the target spans several wavelengths. =Axlq 18:50, 5 July 2007 (UTC)
Article is too hard to understand
[edit]Wikipedia isn't just for specialists in... god knows what it's called "Radarography" lol, it's for uneducated people to educate themselves too. Now I've been reading up on radars at HowStuffWorks.com and I still don't understand this article. I know essentially that a large RCS means a big blip on the radar screen at home receiving its "rays" or whatever, that bounced off a plane it zapped for example. But I didn't learn that from here, take for instance the opening line. It says;
Radar cross section (RCS) describes the extent to which an object reflects an incident electromagnetic wave. It is a measure of the strength of the radar signal backscattered from a "target" object for a given incident wave power.
WTF is a "incident electromagnetic wave"?, I know "electromagnetic" is linked but it doesn't explain this incident wave thing. What's backscattering? Then it hits you with a "given incident wave power"!
Now I know the opening line has been the subject of some debate recently, but it's not just the opening line. Perhaps we could save the formula in the definitions section for the calculation section, and an example of RCS would be very very helpful. I think we should try and explain the basic concept in very basic terms to dummies like me, in the opening paragraph. Then the rest of the article can be used for all the factual encyclopaedic knowledge. Please don't think stupid of me, I just don't know about radars. I'd love it if someone could send me a condescending dummed down explanation of RCS please, then perhaps we could work together to make the article a bit more easy to understand.Ryan4314 (talk) 21:24, 1 January 2008 (UTC)
dBsm
[edit]Somehow the current article misses a major usage by radar and ECM designers & analysts: the use of dBsm (which has no article at present) to express the measured RCS. There's one implied calculation in the RCS article when it mentions reducing detection range by shrinking the RCS, but the actual math is omitted. Using dBsm instead of a straight ratio could make it more understandable, if the two-way radar range equation is brought into it. Also, the image given at the top of the article of an aircraft RCS has no units shown; I bet they are dBsm though. Please consider adding this kind of info, and an article on dBsm that links to both RCS and decibel. I've just posted something similar on the decibel article talk page.
Reference: dBsm@everything2.com
138.163.0.42 (talk) 18:20, 8 July 2008 (UTC)
I put an entry for dBsm on the decibel page, and changed the phrase at the intro of the article from "RCS is the unit of measure of" to "RCS is a measure of". That's because RCS is itself NOT a unit of measure; I know of no way that it's quantified in something other than square of a length unit or dBsm. 138.163.0.43 (talk) 17:11, 6 August 2008 (UTC)
radar cross section
[edit]sir, i want to know about more . on that topics because no person clear the concept what actually it is i have to many question like on what it depend? and more............. plsssssss suggest me more idea about that. —Preceding unsigned comment added by 117.197.17.67 (talk) 16:07, 14 October 2008 (UTC)
Definition of RCS on this page is not correct
[edit]Hi, I noticed that the definition of RCS on this page is currently not correct.
It says: "Radar cross section of an object is defined as: The cross sectional area of a conductive sphere that would reflect as much energy as the object in question."
However, conductive spheres have nothing to do with RCS. A more correct definition might go like:
"RCS is the area required to intercept the transmitted power density at the target such that when the total intercepted power is re-radiated isotropically, the power density actually observed at the receiver is produced."
The major issue here is that the sigma/(4 pi r^2) term in the radar equation implies that the scattered power is radiated isotropically -- and a sphere (PEC or otherwise) definitely does not scatter incident plane wave power isotropically.
Also, I am pretty sure the simple definition of sigma as 4 pi Pbackscatter/Pintercepted cannot be correct because it is not dimensionally correct -- sigma has the units of area (i.e., meters squared).
I have a 1970 copy of Radar Handbook edited by M.I. Skolnick handy, and I will quote section 27-2 (which describes a monostatic case with G = Gr = Gt):
"sigma = ((4 pi)^3 r^4 Pr)/(Pt G^2 lambda^2)"
. . .
"...and radar cross section has the dimensions of area. The concepts embodied in the above definition are those employed in formulating the radar-range equation for received power and area as follows:
1. The establishment of local power density at the target by the transmitter and its antenna. This is represented by the factor G Pt / (4 pi r^2) and is measured in watts per unit area.
2. The capture of a portion of the incident flux and its reradiation to account for a dimensionless factor sigma/(4 pi r^2). A hypothetical area sigma is defined in terms of isotropic reradiation to yield the observed power flux density at the receiver." —Preceding unsigned comment added by Double helix (talk • contribs) 05:59, 27 February 2009 (UTC)
- You have my blessing to fix it then, but for the love of god keep it simple. This is meant to be an encyclopaedia for people who don't know about these things. I have no idea what you just said, nor what the current article is talking about (see my above thread). Ryan4314 (talk) 15:14, 27 February 2009 (UTC)
OK I took my best shot at fixing it and making it understandable. With regard to your previous comment: I think it's folly to try to understand RCS outside of the context of radar and radio engineering. If a reader is wondering what an EM wave is, then he or she should go back to understand that basic concept before attempting to apply it to a higher concept. EM is pretty abstract and obtuse in general, but I don't think accuracy should be sacrificed for the sake of understandability. A pretty famous guy once said "Things should be simple as possible, but no simpler." —Preceding unsigned comment added by 76.113.74.131 (talk) 22:46, 28 February 2009 (UTC)
PS there's a Wiki on EM waves and radiation http://wiki.riteme.site/wiki/Em_wave perhaps this article needs to link to more background info on radio engineering? —Preceding unsigned comment added by 76.113.74.131 (talk) 23:41, 28 February 2009 (UTC)
Seemingly contradictory sentences
[edit]In the last paragraph of the "Definition" section of this article, there seem to be two mutually exclusive statements back-to-back:
"... RCS is an extremely valuable concept because it is a property of the target alone..."
"... RCS is a strong function of the orientation of the radar and target, or, for the bistatic, a function of the transmitter-target and receiver-target orientations."
From the first statement, it appears that RCS is a constant for the specific airframe (independent of orientation, velocity, etc.). From the second, it seems that it is changed by external factors. I don't know which is right, so somebody who knows, please look into this.
Side note, I've always understood that relative velocity is a big factor in detection by modern radars. Targets which move more quickly relative to the radar source are more easily discovered. Is the velocity factored into the Pt? 75.170.61.39 (talk) 21:44, 11 May 2009 (UTC)
I'm the author of those two sentences. I guess they sound like a contradiction, but let me draw a distinction that will clear it up (hopefully). When I say RCS is a property of the target alone, I mean that it does not depend on the performance parameters of the radar (e.g., antenna gains or transmit power). In this light, RCS can be viewed as an intrinsic property of a radar target alone. Now just thinking of the monostatic case for simplicity: the target RCS is indeed a function of viewing angle, however, this again can be viewed as an intrinsic property of the target alone -- the radar just happens to be sampling the RCS value at the radar-target orientation angle.
Just think of rolling a gambling die: there are six faces, each with a distinct number of dots, and we'd normally think of this as a property of the die alone. However, the number of dots you actually see depends on your viewing angle. —Preceding unsigned comment added by 76.113.74.131 (talk) 04:39, 14 May 2009 (UTC)
Well, that makes more sense. But in the second sentence, would it not be more correct then to say that the returned power is a function of viewing angle, etc.? Maybe I'm missing something still. And thanks for the reply. This subject is not my area of expertise in any sense. 75.170.61.39 (talk) 06:25, 14 May 2009 (UTC)
Me again. RCS is essentially a highly-normalized unit of returned power. I can't really say it'd be more correct to make your suggested change. Let me give it some thought and see if I can phrase/explain it better. —Preceding unsigned comment added by 76.113.74.131 (talk) 04:31, 23 May 2009 (UTC)
PS: About velocity -- RCS is independent of target velocity, however, there is another reason why a moving target might be more easily detected, and it has to do with signal processing that occurs within the radar receiver. A moving target imparts a small frequency shift (Doppler shift) on the radar signal. In a lot of radar applications, radar reflections from unwanted targets (known as clutter) such as stationary trees and mountains and the like do not have this frequency shift, thus, a moving target return is distinuishable from clutter returns. —Preceding unsigned comment added by 76.113.74.131 (talk) 04:40, 23 May 2009 (UTC)
Definition Wrong (Again)
[edit]Hey folks, I removed:
"Informally, the RCS of an object is the cross-sectional area of a perfectly reflecting sphere that would produce the same strength reflection as would the object in question. (Bigger sizes of this imaginary sphere would produce stronger reflections.) Thus, RCS is an abstraction: The radar cross-sectional area of an object does not necessarily bear a direct relationship with the physical cross-sectional area of that object but depends upon other factors."
from the article because it is wrong in general. Please do not put this wrong info back in the article. RCS has nothing to do with perfectly conducting spheres, real or imagined. If you look at a Mie series, which is an analytical solution for the RCS of a sphere, at high frequencies the RCS does approach the geometrical cross section of the sphere. But when the sphere is not many wavelengths in radius, this is not true, and thus the statement I removed is false. —Preceding unsigned comment added by 68.35.14.57 (talk) 03:13, 1 February 2010 (UTC)
- The wikipedia is based on reliable sources. You are not a reliable source, you're just an insulting opinionated anonymous coward who is probably going to get suspended soon.- Wolfkeeper 12:26, 1 February 2010 (UTC)
Definition Still Wrong...
[edit]Well, it looks like you're pretty good at name calling, yourself. I will now enlighten you with a citation. According to Balanis, Advanced Engineering Electromagnetics, John Wiley & Sons, 1989, section 11.3, p. 577, "The echo area or RCS is defined as the area intercepting the amount of power that, when scattered isotropically, produces at the receiver the power density that is equal to the density scattered by the actual target." This is a standard graduate engineering E&M text. Note that Balanis does not say anything about spheres. That's because defining RCS this way is wrong. Not "informal", but wrong. As has now been noted several times, the fact that the RCS of a sphere approaches its geometrical cross section at high frequencies is basically a mathematical coincidence and does not imply much about the nature or definition of RCS. For example, the RCS of an airplane does not approach its geometrical cross section at high frequencies. If it did, the F-117 would've been worthless and the only recourse for RCS reduction would be to build a smaller airplane.
So I'm growing tired of arguing with you. If you want to be a stubborn bully and keep this plainly wrong definition here, then that's fine by me. But it's a little like seeing someone throw a piece of trash down on the ground in a public park. No, it doesn't really hurt me that much, but it does make the world a worse place for everyone.
I'm not worried about being banned since I'm on DHCP. Take care, and I hope you never have to do any calculations of RCS that matter in the real world. —Preceding unsigned comment added by 68.35.14.57 (talk) 04:34, 4 February 2010 (UTC)
De Havilland Mosquito was a wooden plane
[edit]less radar signature / profile due to the wood construction ?
[edit]Did the fact that much of that plane was made of wood influence its visibility by radar ? There is much speculation about that in the web (and many people affirm / approve that "automatically). Has anoyone profound knowledge about that ? If yes, I would be glad about a notice at my discussion page to add that information to Wikipedias in de, en and fr. The Mosquito was produced 7781 times ; therefore I hope material about that question exists.
Thanks --Neun-x (talk) 05:53, 6 February 2013 (UTC)
- yes it did - see here:
- " ... was the daylight incursions by the RAF's Mosquitoes: flying high and fast, they were at first beyond the reach of German fighters, and being made of wood, gave only a weak radar echo." from Germany and the Second World War: Volume VII - page 166. — Preceding unsigned comment added by 2.24.205.73 (talk) 10:22, 27 August 2014 (UTC)
possible lead re-write
[edit]The current lead seems a bit unwieldy with the bulleted list and equations. here is a possible re-write: [1]. With no objections, I will add this to this article in a couple weeks or so. Mysticdan (talk) 18:33, 16 December 2016 (UTC)
Requested move 24 May 2023
[edit]- The following is a closed discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. Editors desiring to contest the closing decision should consider a move review after discussing it on the closer's talk page. No further edits should be made to this discussion.
The result of the move request was: Moved (non-admin closure) >>> Extorc.talk 14:31, 30 May 2023 (UTC)
Radar cross-section → Radar cross section – For consistency with Cross section (physics) (instead of "cross-section"). fgnievinski (talk) 20:09, 24 May 2023 (UTC)
- Support. No brainer.
- Dondervogel 2 (talk) 21:33, 24 May 2023 (UTC)
Unsigned comment (18 Nov 2024)
[edit]With the definition of RCS in mind the statement in the article the following statement made in the section about Measurement of RCS is also obviously flawed, quote: "A perfectly conducting sphere of projected cross sectional area 1 m2 (i.e. a diameter of 1.13 m) will have an RCS of 1 m2." If the power is radiated isotropically then this statement CANNOT be true because a perfectly conducting sphere does NOT reflect/ radiate the power isotropically but does so with directionally varying intensity! The quotes statement, as some other statements in the article, is not only flawed but very misleading and rather nonsensical. The RCS has absolutely NO relation to the laws of physics involved in signal reflections whatsoever. It is merely a formula based on an oversimplified model which (despite being unrelated to the physics involved) happens to be very useful for comparisons, but it happens to be commonly misinterpreted and greatly misunderstood in public discussions and information about RCS and/or stealth technologies.