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| '''Range ambiguity resolution''' is a technique used with medium [[Pulse repetition frequency]] (PRF) radar to obtain range information for distances that exceed the distance between transmit pulses.
| | Many people rent Videos to view with the friends and family daily. Usually this carried out at a relevant video local rental place. Now there can be a style of renting videos from a vending instrument often known as Redbox.<br><br>There is the huge help to writing within a busy niche: you very likely be able to take advantage of pre-existing web-site visitors. If there is a rabid group of folks eager to mention setting up an at-home design business, your information product on tax guidelines for the at-home artist-entrepreneur has a ready-made customer base.<br><br>One major downside to selling on amazon is always there are a lot of product confines. Apparel and accessories are two huge categories that are restricted specific sellers. You can email Amazon to try to get authorization to sell in the restricted categories, but there are no means. On eBay, you free to market just about anything. Anyone have typically sell items get been in Amazon's restricted areas, Amazon probably doesn't work which.<br><br>If you adored this post as well as you would want to obtain guidance with regards to [https://www.youtube.com/watch?v=jZ-rP3WK7bo amazing selling machine video 4] i implore you to check out our web site. Add to this the truth with information selling, perform resell just as "packet" of materials time after time again to as quite a few individuals who want it, you have an unstoppable income force! However, it's vital that remember that technology a good ever expanding field. So you will have to "change more than times" and be prepared assistance your information up up to now. Change is a good affair.<br><br>Comply with the regulations. By this I mean comply with distance selling regulations, privacy regulations, and website accessibility etc etc. Comply as and the can to construct a more advantageous amazing selling machine.<br><br>Internet seriously isn't for selling physical products online. With the increment of unstoppable computer technology, you'll be able to show your specific hobby in any shape through any platform. You can try to use video link, e-book, images, patterns etc. Those kinds of technologies may make your life easier. Signifies that do not have to manage your company physically. This could be created by clicking during your computer mouse only. Obstacles and fences that just a few ingredients to browse through in running business [http://browse.Deviantart.com/?qh=§ion=&global=1&q=offline offline] can be minimized through Internet.<br><br>The unique thing about the BJC-80 simple fact its greatest attributes are optional some. In other words, you might need to pay extra for them. If you purchase a new unit, these extra purchases won't cost much. Should you be buying used, then there's a good chance they will already be included, so there won't be any extra charge. So, what are these optional features? The actual first is a rechargeable battery, as this can be a great convenience during the route. The other is a scanning attachment, will be extremely scarce for mobile printers. The scanning attachment is an IS-12 Color Image Scanner cartridge.<br><br>For "acceptable," it could be a bit less perfect, but yes, it still needs for basically okay. Broken spines are a certain no-no! If in doubt, keep it or rate it away. Don't risk ruining your testimonials. |
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| This signal processing technique is required with [[pulse-Doppler radar]].<ref>{{Cite web|url=http://web.mit.edu/jync/www/ll/JTECH1805.pdf|title=Multi-PRI Signal Processing For The Terminal Doppler Weather Radar. Part II: Range-Velocity Ambiguity Mitigation.|publisher=MIT}}</ref><ref>{{Cite web|url=http://cimms.ou.edu/rvamb/home.htm|title=Radar Range Velocity Ambiguity Mitigation|publisher=Cooperative Institute for Mesoscale Meteorological Studies, University of Oklahoma}}</ref><ref>{{Cite web|url=http://www.nssl.noaa.gov/papers/dopplerguide/|title=A Guide for Interpreting Doppler Velocity Patterns|publisher=National Oceanic and Atmospheric Administration}}</ref>
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| The raw return signal from a reflection will appear to be arriving from a distance less than the true range of the reflection when the wavelength of the pulse repetition frequency (PRF) is less than the range of the reflection. This causes reflected signals to be '''folded''', so that the apparent range is a '''[[Modular arithmetic|modulo function]]''' of true range.
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| ==Definition==
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| Range aliasing occurs when reflections arrive from distances that exceed the distance between transmit pulses at a specific [[pulse repetition frequency]] (PRF).
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| Range ambiguity resolution is required to obtain the true range when the measurements are made using a system where the following inequality is true.
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| :<math>Distance > \left (\frac {C}{2 \times PRF} \right)</math>
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| The range measurements made in this way produces a [[modular arithmetic|modulo]] function of the true range.
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| :<math>Apparent \ Range = (True \ Range) MOD \left (\frac {C}{2 \times PRF} \right)</math>
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| ===Theory===
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| To find the true range, the radar must measure the apparent range using two or more different PRF.
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| Suppose a two PRF combination is chosen where the distance between transmit pulses (pulse spacing) is different by the pulse width of the transmitter.
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| :<math> Two \ PRF \ Combination \begin{cases} Pulse \ Spacing \ (Ambiguous \ Range) = \frac{1}{PRF} \\ \\ \frac{1}{PRF_A} - \frac{1}{PRF_B} = \pm \ Transmit \ Pulse \ Width \end{cases}</math>
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| Each transmit pulse is separated in distance the ambiguous range interval. Multiple samples are taken between transmit pulses.
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| If the receive signal falls in the same sample number for both PRF, then the object is in the first ambiguous range interval. If the receive signal falls into sample numbers that are different by one, then the object is in the second ambiguous range interval. If the receive signal falls into sample numbers that are different by two, then the object is in the third ambiguous range interval.
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| The general constraints for range performance are as follows.
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| Each sample is processed to determine if there is a reflected signal (detection). This is called signal detection.
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| The detection made using both PRF can be compared to identify the true range. This comparison depends upon the transmitter duty cycle (the ratio between on and off).
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| The [[duty cycle]] is the ratio of the width of the transmit pulse width <math>\Tau</math> and the period between pulses <math>1/PRF</math>.<ref>[http://www.doctronics.co.uk/555.htm "555 timer"], ''Doctronics'', accessed 2011-03-23</ref>
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| :<math> \begin{align} Transmitter \\ Characteristics \end{align} \begin{cases} Duty \ Cycle = PRF \times Transmit \ Pulse \ Width \\ \\ Pulse \ Spacing = \left( \frac {C}{PRF} \right)\end{cases}</math>
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| Pulse-Doppler can reliably resolve true range at all distances less than the '''Instrumented Range'''. The optimum pair of PRF used for a pulse-Doppler detection scheme must be different by a minimum of <math>PRF * Duty Cycle</math>. This makes the range of each PRF different by the width of the sample period.
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| The difference between the sample numbers where reflection signal is found for these two PRF will be about the same as the number of the ambiguous range intervals between the radar and the reflector (i.e.: if the reflection falls in sample 3 for PRF 1 and in sample 5 for PRF 2, then the reflector is in ambiguous range interval 2=5-3).
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| :<math>\begin{align}Instrumented \\ Range \end{align} \begin{cases} Minimum \ Sample \ Width = \left( \frac{Duty \ Cycle}{PRF} \right) \\ \\ Maximum \ Distance = \left( \frac{Pulse \ Spacing}{Sample \ Width}\right) = \left( \frac{C}{Sample \ Width \times 2 \times PRF^2}\right) \\ \\ Samples \ Per \ Transmit \ Pulse = \left( \frac{1}{Minimum \ Sample \ Width} - 1 \right) \end{cases} </math>
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| There is no guarantee that true range will be found for objects beyond this distance.
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| ===Operation===
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| The following is a special case of the [[Chinese remainder theorem]]. | |
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| Each ambiguous range sample contains the receive signal from multiple different range locations. Ambiguity processing determines the true range.
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| This is explained best using the following example, where PRF A produces a transmit pulse every 6 km and PRF B produces a transmit pulse every 5 km.
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| {| class="wikitable"
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| ! Transmit !! 1 km Sample !! 2 km Sample !! 3 km Sample !! 4 km Sample !! 5 km Sample
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| The apparent range for PRF A falls in the 2 km sample, and the apparent range for PRF B falls in the 4 km sample. This combination places the true target distance at 14 km (2x6+2 or 2x5+4). This can be seen graphically when range intervals are stacked end-to-end as shown below.
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| {| class="wikitable"
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| ! 0!! 1!! 2!! 3!! 4!! 5!! 6!! 7!! 8!! 9!!10!!11!!12!!13!!14!!15!!16!!17!!18!!19!!20!!21!!22!!23!!24!!25!!26!!27!!29!!29
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| | || || A|| || || || || || A|| || || || || || A|| || || || || || A|| || || || || || A|| || ||
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| | || || || || B|| || || || || B|| || || || || B|| || || || || B|| || || || || B|| || || || ||B
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| |}
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| "A" represents target range possibilities for PRF A, and "B" represents target range possibilities for PRF B.
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| This process uses a look-up table when there is only one detection. The size of the table limits the maximum range.
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| The process shown above is a type of digital [[convolution]] algorithm. | |
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| ==Limitations==
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| This technique has two limitations.
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| * Blind Zones
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| * Multiple Targets
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| The process described above is slightly more complex in real systems because more than one detection signal can occur within the radar beam. The pulse rate must alternate rapidly between at least 4 different PRF to handle these complexities.
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| ===Blind Zones===
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| Each individual PRF has blind ranges, where the transmitter pulse occurs at the same time as the target reflection signal arrives back at the radar. Each individual PRF has blind velocities where the velocity of the aircraft will appear stationary. This causes [[Radar scalloping|scalloping]], where the radar can be blind for some combinations of speed and distance.
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| * [[Radar_scalloping#Pulse-Doppler_Radar|Radar scalloping detailed explanation]]
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| A four PRF scheme is generally used with two pair of PRF for the detection process so that blind zones are eliminated.
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| The antenna must dwell in the same position for at least three different PRF. This imposes a minimum time limit for the volume to be scanned.
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| ===Multiple Targets===
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| Multiple aircraft within the radar beam that are separated by over 500 meters introduces additional [[Degrees of freedom (physics and chemistry)|degrees of freedom]] that requires additional information and additional processing. This is mathematically equivalent to multiple unknown quantities that require multiple equations.
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| Doppler frequency shift induced by changing transmit frequency reduces unknown degrees of freedom.
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| Sorting detections in order of amplitude reduces unknown degrees of freedom.
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| Ambiguity resolution relies on processing detections with similar size or speed together as a group.
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| ==References==
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| {{Reflist}}
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| [[Category:Radar]]
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