Talk:Synthetic-aperture radar

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Section sizes

Section size for Synthetic-aperture radar (67 sections)
Section name	Byte count	Section total
(Top)	2,980	2,980
Motivation and applications	3,239	3,239
Basic principle	3,780	3,780
Algorithm	977	977
Existing spectral estimation approaches	770	19,718
Non-parametric methods	32	8,991
FFT	1,882	3,057
Advantages	1,004	1,004
Disadvantages	171	171
Capon method	2,622	3,430
Advantages	510	510
Disadvantages	298	298
APES method	1,627	2,472
Advantages	695	695
Disadvantages	150	150
SAMV method	619	974
Advantages	218	218
Disadvantages	137	137
Parametric subspace decomposition methods	51	3,158
Eigenvector method	1,334	1,495
Advantages	84	84
Disadvantages	77	77
MUSIC method	1,129	1,612
Advantages	389	389
Disadvantages	94	94
Backprojection algorithm	785	4,132
Advantages	1,075	1,075
Disadvantages	212	212
Application: geosynchronous orbit synthetic-aperture radar (GEO-SAR)	2,060	2,060
Comparison between the algorithms	1,693	1,693
Multistatic operation	1,547	1,547
Scanning modes	22	3,243
Stripmap mode airborne SAR	770	770
Spotlight mode SAR	1,267	1,267
Scan mode SAR	1,184	1,184
Special techniques	24	20,228
Polarimetry	1,400	7,647
SAR polarimetry	1,540	1,540
Three-component scattering power model	1,290	1,290
Four-component scattering power model	3,417	3,417
Interferometry	3,402	6,865
Differential interferometry	2,228	2,228
Tomo-SAR	1,235	1,235
Ultra-wideband SAR	3,251	3,251
Doppler-beam sharpening	1,416	1,416
Chirped (pulse-compressed) radars	1,025	1,025
Typical operation	139	9,713
Data collection	431	5,925
Image resolution and bandwidth	1,332	1,332
Image resolution and beamwidth	2,112	2,112
Pulse transmission and reception	2,050	2,050
Data processing	453	3,649
Amplitude data	374	374
Phase data	256	256
Coherence speckle	688	688
Optical holography	1,878	1,878
Image appearance	382	6,492
Range, cross-range, and angles	1,298	1,298
Visibility	2,159	2,159
Mirroring artefacts and shadows	1,015	1,015
Objects in motion	1,638	1,638
History	63	63
Relationship to phased arrays	3,879	3,879
See also	807	807
References	30	30
Bibliography	1,130	1,130
External links	871	871
Total	78,697	78,697

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NT at Umbra (talk · contribs) has been paid by Umbra Space.

Maximum Resolution[edit]

First of all I found it amazing that holograms were being used to perform analog computations on datasets. How long ago was this being done? Does anyone know?

Seondly the resolution quoted in the article is 0.6 meter. If we were doing it at 0.6m resolution back then what's the maximum resolution attainable now? —Preceding unsigned comment added by 24.80.86.98 (talk) 18:58, 22 January 2008 (UTC)[reply]

I saw the JPL laser in 1977 and it was still there in 1982. Can't say about others. Resolution depends on the balance of wavelength, and other system design factors. Lots of interest in X-band isn't based on a shorter wavelength than say L-band. 171.66.48.97 (talk) 00:32, 27 May 2010 (UTC)[reply]

Regarding the first paragraph above -- the optical hologram idea was older than the radar developments described, but was incomplete. E. Leith devised the successful radar data-processing scheme, for turning film-recorded coherent-radar data into visual images, before applying his understanding of that process to turning film-recorded coherent light-wave data into visual images. See particularly the historical article by Leith that is in the list of references.Oldteched (talk) 01:56, 12 May 2012 (UTC)[reply]

Doppler Beam Sharpening[edit]

Is this really compatible with SAR? The Doppler shift from targets ahead/behind seems like it is actually the same effect as the phase shift that is used to assemble multiple samples. For a sidelooking radar that is not a SAR, it's clear this could help. --Andrew 18:54, Dec 14, 2004 (UTC)

Doppler Beam Sharpening[edit]

Hmmm... I'm not sure if I understand your question, but let me say (from many years of experience) that most SAR radars use doppler beam sharpening.

Let me first say that it is EXTREMELY DIFFICULT to separate frequency shift from phase shift... at the time the shift is occurring. After the fact it's not a problem, but with a dynamic signal, it's nigh impossible to separate the two... This "reality" is often used with FM radios - in that the same receive chain detects either PM (phase modulation) or FM with little difference...

Now as to the whole issue of dopper shifts... maybe it helps to separate the different contributing components (simplified). First, there are the two large scale doppler components: motion of the imaging platform and motion of "point" targets in the area being imaged. Normally (when MTI is not the intended capability) you'd like the point target to have no motion. Then there are the two "microdoppler" components: vibrations that cause spreading of the doppler signature - either by the imaging platform or by any point target vibrations. Unless you are taking advantage of microdoppler signature analysis then you'd just as soon these components were zero. Finally there are the periodic rotational/translational components - think of these as periodic movements on the target or imaging platform... actually used with benefit in ISAR imaging of ships (waves and swells cause regular rotational and translational displacements).

Now, if the goal is GROUND/SURFACE imaging... then typically... all the doppler components except the imaging platform - are assummed to be zero (as I said, simplified... we ignored yaw, roll, and pitch changes by the imaging platform - which all make life more difficult)... This has proven to be a resonable assumption in real world SAR systems. Never-the-less, imaging platforms do record/transfer the three space coordinates, three space accellerations, three space pitch/roll/yaw rates, and three space pitch/roll/yaw accelerations. GA maps also play a roll (GA = gravitational anomaly) to ensure the Z accelerations are normalized...

A complicated but interesting subject in itself. Anyway, many SAR systems treat the phase change as a frequency change by using DFT/FFT processing to determine the doppler shift amounts. This means that given a single range gate time period, the number of actual bins relates to the processing power available and the phase/frequency resolution (A/D speed, bits of resolution, linearity)... Obviously there are diminishing returns while working with all this that are fed by real energy beam width... i.e.... if the transmitted signal is way down when 15 degrees off orthonormal... then why bother to process data that would have doppler shifts that correlate to that far off axis... think in terms of basic trig... if the range gate being processed is 100 km away (60+ miles), the system has a ten meter "resolution" - - and the real beamwidth is 20 degrees... (+/- 10 degrees)... then the total number of bins that needs to be processed (tan "theta" = Opposite/Adjacent... since we know theta = 20 degrees and the adjacent side is 100,000 meters (100 km)... then the Opposite side is approximately 35,000 meters long... (simple triangle)... with 10 meter bins... then we're looking at 3,500 angular bins... just along that one range resolution cell... that must map into 3,500 discrete phase/frequency shifts... or 1750 discrete upshifted bins and 1750 discrete downshifted bins...

Anyway... as I digressed WAY TOO MUCH... Doppler beam sharpening... is exactly how many SAR systems actually do their imaging... (mapping mode - - - spot modes are another story)....

No.[edit]

Doppler beam sharpening is also called "unfocussed SAR" and it means that everything with a doppler shift >x is filtered out - so everything that is out of the center of the main beam is discarded. It is a simplified version of SAR.

ISAR[edit]

What's an Inverse Synthetic Aperture Radar? [1] Ojw 10:56, 6 October 2005 (UTC)[reply]

Inverse SAR uses the motion of the target to create a image. We plot range and doppler shift. Ships at sea can be imaged very easily, but since the velocity is not known ahead the images are pretty distorted. Dominick 11:40, 6 October 2005 (UTC) This link is broken!!! reference for you (to be added later) Dominick 11:47, 6 October 2005 (UTC)[reply]

The real answer[edit]

I want to point-out that my answer is more valid not because it has more merit or a greater factual basis but because it mine..... Just kidding, However these are my thoughts.

The processing is similar but the techniques are different. In fact they are opposites of each other; DBS integrates within a beam and SAR integrates out with the beam (or near enough). So what this means is that with DBS is synthesises a smaller beam width by taking pulse intervals within the beam spread and SAR takes pulse sample with a small overlap synthesising a larger antenna. The net result is the same and this is why the processing is similar for strip map and spot light but the techniques are opposite to each other. The difference is notable when you consider Scanned DBMS, or when you calculate the PRF and samples requires against a resolution for a given scenario.

UWB SAR[edit]

The section on UWB SAR contains two false statements that I will correct:

First, "Interpretation of the [narrow band radar] results is also eased by the fact that the material response must be known only in a narrow range of frequencies", is false in that the frequency response information is still present in a UWB echo, and can easily be considered in processing.

Strangely, the writer goes on to admit this fact, and presents it as a disadvantage!...

Second, "but much of the information is concentrated in relatively low frequencies (with long wavelengths). Thus such systems require very large receiving apertures to obtain correspondingly high resolution along the track." is also false. The large apertures are "required" only if one desires to detect that low-frequency information--it certainly isn't "necessary" to retrieve that information just because UWB SAR happens to provide the information while narrow-band SAR does not! Fleem (talk) 11:56, 9 May 2008 (UTC)[reply]

"Combining the series of observations requires significant computational resources. It is often done at a ground station after the observation is complete, using Fourier transform techniques. The high computing speed now available allows SAR processing to be done in real time onboard SAR aircraft." This is kinda contradictory. If it's the case that it used to be done on the ground, but is now done in the air, please correct. I'm sure there's a good explanation, but I'm not sure what it is, so I'm putting a contradiction tag here. —Preceding unsigned comment added by 75.209.152.30 (talk) 14:34, 29 December 2008 (UTC)[reply]

Much nonsense here[edit]

Much nonsense here:

"The equivalence of these two methods can be seen by recognizing that multiplication of sinusoids can be done by summing phases which are complex-number exponents of e, the base of natural logarithms."
This makes not one whit of sense because a phase is merely a number, and summing phases yields nothing but another number. Multiplication of sinusoids has nothing to do with "summing phases" or (adding up) any other kind of a number. Also, phases are real numbers, and they do not have anything to do with "complex-number exponents of e", which are generally complex numbers themselves.

Furthermore, this article is nonsense without any diagrams that show what is going on, and also nonsense without any equations. Trying to explain or describe synthetic aperture radar entirely in words is a fool's errand. The fact that "e" is the base of natural logarithms needs to be taken as a given. The reader should be assumed to know what Euler's identity states.
98.67.110.231 (talk) 03:07, 29 July 2012 (UTC)[reply]

Extreme nonsense here[edit]

It seems to me that the "authors" of this article have compiled layer and layer of jargon on top of unnecessary complexity, without adding a single thing to the article's readability. I am continually amazed at how dumb some "smart" people can be. And if it's not dumb - then it's worse than that: it's arrogance. The vast majority of technical articles here are not written to explain how something works, but rather to demonstrate how much the author knows and how magnificently that author can obfuscate the obvious. — Preceding unsigned comment added by 98.194.39.86 (talk) 03:20, 6 April 2013 (UTC)[reply]

The history sections looks OK, but the technical material is very questionable. The "Algorithm" section is either a very eccentric formulation of SAR, or it's a joke or vandalism by someone. It needs to be entirely replaced. DonPMitchell (talk) 19:04, 2 February 2016 (UTC)[reply]

Yes, the Algorithm section is certainly a strange way of looking at SAR. I'll spend some time this weekend re-writing it with a more standard approach. Mysticdan (talk) 21:44, 2 February 2016 (UTC)[reply]

Just to reanimate this discussion: I have attempted to fix the "Algorithm" section. I've been aware for some time that it is nonsense and I've finally got around to replacing it with something short, sourced and I believe more accurate. Theoh (talk) 22:06, 14 January 2023 (UTC)[reply]

This article needs your help[edit]

This article is in need of help, and there is only so much I can do – but YOU can help! Here are some suggestions if you want to improve this article:

Include some informative images. Look for images in Wikipedia/Commons, e.g. here.
The text is much much too long and much too "winding" – the information should be presented much shorter and much more concise. Wikipedia is an encyclopaedia, after all.
Links to other relevant articles should be added.
Better structure

A suggestion for a structure would be:

Applications: For what is SAR used, with examples
Technology: Some details how SAR works, the different types of SAR, differences to other radar technologies, and so on
History: How it started, how it was developed over time, and so on.

A final suggestion: Feel free to delete any of those long and winding passages of text currently present, and replace them with new and concise text of your own.

Tony Mach (talk) 13:33, 12 June 2014 (UTC)[reply]

Google translate does a pretty good job with that figure:
Top: Equivalent phased-array antenna
Middle: Synthetic aperture length
Description: The distance to the target is different between the positions of the platform. If the target is on the central axis of the real aperture, the distance is less than if the real antenna must squint toward the target. This expresses itself in a phase difference Δφ. For a sharp picture, the phase difference between the position C and the other positions must be corrected in the image processing software. — Preceding unsigned comment added by Mysticdan (talk • contribs) 17:11, 11 November 2015 (UTC)[reply]

The English version is available. However, it would be better to create this file in SVG format with international labeling. --c.w. (talk) 18:36, 24 January 2023 (UTC)[reply]

Please: a picture for the "image appearance" section[edit]

It is absolutely necessary to provide a picture for the section "Image appearance". This is an extremely important section, but without pictures, it is too hard to understand. Statisticastatistico (talk) 20:42, 16 May 2016 (UTC)[reply]

Copy paste copyvios[edit]

This edit by J2691 (talk · contribs) again re-introduces copy and pasted text to this article. This needs to stop. Just because it's published by NATO does not make it public domain. I am left to assume that large chunks of that text is also a copyvio. ie. "3D SAR Tomography, also known as 3D SAR focusing or 3D SAR imaging, represents a very recent improvement of SAR interferometry that allows obtaining additional information from multi-baseline SAR dataset by overcoming the limitation of available techniques" is a direct copy paste from Tomographic SAR. --Dual Freq (talk) 22:10, 15 November 2016 (UTC)[reply]

Hi, I am new to wikipedia and I am sorry for any inconvenience. I cited the reference for 3-D tomography, but wasn't aware about it being referred as duplicate. I will write that part differently, immediately. I have taken information from various papers but tried to edit the content as possible and cited references whereever required. Please guide me with any other issues. Appreciate your help. comment added by J2691 (talk • contribs) November 15, 2016 (UTC) — Preceding unsigned comment added by J2691 (talk • contribs)

A good place to start would be remove the material you copied from the article. --Dual Freq (talk) 23:28, 15 November 2016 (UTC)[reply]

Comment on History Section[edit]

There is some information on MDA website that seem to suggest far better imagery was already achieved in 1957.

See the "Did you know?" section on this page? Can this image be verified to be attributable to MDA? Can the date be verified - if so - it will certainly be worth showcasing that result here on the wikipedia page

http://www.mdaus.com/intelligence,-surveillance-and-reconnaissance/synthetic-aperture-radar-(sar) An aerial SAR image (on the left) taken in 1957 of a Volkswagen Beetle compared to an aerial photograph (picture on the right) illustrates the power of SAR applications from the earliest applications — Preceding unsigned comment added by 146.64.81.115 (talk) 13:33, 26 January 2017 (UTC)[reply]

spelling[edit]

Typically, synthetic aperture radar is spelled as 'synthetic aperture radar' i.e., without the '-'.

Split of history into History of synthetic-aperture radar (done)[edit]

I think that the proposed split into History of synthetic-aperture radar would make a lot of sense as the page is currently too long and there is enough information to support a history page.Gusfriend (talk) 04:12, 19 February 2022 (UTC)[reply]

I agree. It would be suitable to split it off.

KinneticSlammer (talk) 11:37, 5 April 2022 (UTC)[reply]

I've gone ahead and made the split. – Scyrme (talk) 13:32, 13 August 2022 (UTC)[reply]

Adding an image[edit]

Hi editors, what would you think about adding File:Hoover Dam 50 cm Resolution Synthetic Aperture Radar Image.jpg to the Image appearance section? Right now, the article has outdated SAR imagery and does not have any recent examples of high-resolution SAR imagery. This 50 cm high resolution image of the Hoover Dam shows an example of modern SAR imagery and adds context to current capabilities. Let me know what you think! I work for Umbra, the company that took the image, so I wanted to see if someone would add it on my behalf. We're not looking for any credit or PR—we'd like to help keep the article up-to-date. If you have a suggestion for a different image(s), I'm open to providing it.

@Graeme Bartlett, pinging you since we've talked about images in case you would like to take a look.

Thanks in advance for your help! NT at Umbra (talk) 16:05, 13 July 2023 (UTC)[reply]