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Slide Text Space SUBMIT ALL submit all SUBMIT submit Submit Unmute volume instructor: andy wood transmitting & receiving characteristics principles of doppler weather radar review lesson take your time and review the lesson content provided in this presentation. review lesson technical problems? if you encounter any technical problems with this lesson, please contact the rac team directly by e-mail at: nws.wdtd.rachelp@noaa.gov technical problems? complete the quiz at the end of this lesson, there is an embedded quiz. complete this quiz by selecting the best answer for each question. you need to correctly answer 70% of the quiz questions to receive completion credit in the lms. complete the quiz course completion review lesson review lesson complete the quiz technical problems? technical problems? introduction in order for nws forecasters to receive credit for this course in the nws learning center, you will need to take the following steps roadmap learning objectives identify the two characteristics determined by the pulse repetition frequency (prf) identify the relationship between prf and pulse repetition time (prt) identify the relationships between prf and maximum unambiguous range and velocity identify the doppler dilemma identify why the wsr-88d has two pulse duration modes identify why the target range equation divides by a factor of 2 identify why range folding (rf) occurs with the wsr-88d transmitting & receiving overview transmitting & receiving characteristics impact accurate: range detection velocity estimates pulse repetition frequency (prf) the number of pulses sent out by the radar per second prf no. prf (s-1) prf no. prf (s-1) 1 446 5 1014 2 802 6 1095 3 857 7 1181 4 926 8 1282 sample doppler prf set (set c): pulse repetition time (prt) time between pulses (prt) prt = 1/prf the time elapsed between two pulses prf no. prt (s) prf no. prt (s) 1 0.0022 5 0.001 2 0.0012 6 0.0009 3 0.0012 7 0.0008 4 0.0011 8 0.0008 maximum unambiguous range (rmax) the distance traveled out & back by one pulse before the next pulse is sent rmax rmax = c 2prf maximum unambiguous velocity (vmax) more frequent pulses = faster speeds required for targets to reach nyquist velocity transmitted pulse phase returned pulse #1 phase returned pulse #2 phase difference in pulse phases { the maximum speed a target needs to move before reaching the nyquist velocity vmax = λprf 4 doppler dilemma fewer pulses = long rmax, but low vmax more pulses = high vmax, but short rmax rmax = c 2prf scanning strategies have been designed to mitigate the doppler dilemma vmax = λprf 4 why the doppler dilemma matters? target range equation time taken for pulse to reach target and get back to radar (t) ***factor of 2 in denominator because we only want one-way distance range = ct 2 pulse duration short pulse (1.57 μsec) long pulse (4.7 μsec) longer pulse duration = more power density (a.k.a. sensitivity) the length of time spent transmitting a pulse range folding max range correct azimuthal location, but incorrect range location range folding example #1 max range target lies within maximum unambiguous range range target will appear will be actual range of target listening period length of time spent listening for radar returns time between end of first pulse and beginning of second pulse short pulse mode = 99.8% long pulse mode = 99.5% velocity estimates less reliable in long pulse mode range folding example #2 target lies outside maximum unambiguous range max range range target will appear based on second pulse faster prf slower prf max range + lower vmax summary transmitting & receiving characteristics impact: range estimates velocity estimates prf/prt determine the rmax & vmax for the pulse (doppler dilemma) pulse duration related to rmax targets located beyond the rmax range folded appear closer to radar than actuality incorrect incorrect. recall two of the equations we looked at which used prf. continue continue continue continue continue continue correct correct! continue continue continue continue continue continue which of the following radar characteristics are determined by the pulse repetition frequency? (choose all that apply) maximum unambiguous range (rmax) maximum unambiguous range (rmax) maximum unambiguous range (rmax) maximum unambiguous range (rmax) maximum unambiguous range (rmax) maximum unambiguous range (rmax) maximum unambiguous velocity (vmax) maximum unambiguous velocity (vmax) maximum unambiguous velocity (vmax) maximum unambiguous velocity (vmax) maximum unambiguous velocity (vmax) maximum unambiguous velocity (vmax) pulse duration pulse duration pulse duration pulse duration pulse duration pulse duration power density power density power density power density power density power density question #1 of 6 incorrect incorrect. look at the table…see how many order of magnitudes the actual reflectivity factor spans?! continue continue continue continue continue continue correct correct! continue continue continue continue continue continue the pulse repetition time (prt) is just the reciprocal of the pulse repetition frequency (prf). true true true true true true false false false false false false question #2 of 6 incorrect incorrect. they are both dependent upon the prf. continue continue continue continue continue continue incorrect incorrect. this makes no sense. continue continue continue continue continue continue incorrect incorrect. nothing is integrated or derived to compute the rmax or vmax continue continue continue continue continue continue incorrect correct! continue continue continue continue continue continue vmax is ___________ the prf, and rmax is ___________ the prf proportional to; inversely proportional to proportional to; inversely proportional to proportional to; inversely proportional to proportional to; inversely proportional to proportional to; inversely proportional to proportional to; inversely proportional to the integral of; the derivative of the integral of; the derivative of the integral of; the derivative of the integral of; the derivative of the integral of; the derivative of the integral of; the derivative of a multiple of; equal to a multiple of; equal to a multiple of; equal to a multiple of; equal to a multiple of; equal to a multiple of; equal to independent of; dependent on independent of; dependent on independent of; dependent on independent of; dependent on independent of; dependent on independent of; dependent on question #3 of 6 incorrect incorrect. the wsr-88d has a slightly lower listening time during long pulse mode continue continue continue continue continue continue incorrect incorrect. rmax does not depend on the pulse duration. continue continue continue continue continue continue incorrect incorrect. velocity estimations are slightly worse for long pulse mode than short pulse mode. continue continue continue continue continue continue incorrect correct! continue continue continue continue continue continue the long pulse duration mode for the wsr-88d exists to ________________________. provide more sensitivity during clear air mode operations. provide more sensitivity during clear air mode operations. provide more sensitivity during clear air mode operations. provide more sensitivity during clear air mode operations. provide more sensitivity during clear air mode operations. provide more sensitivity during clear air mode operations. provide more accurate velocity estimations in clear air mode operations. provide more accurate velocity estimations in clear air mode operations. provide more accurate velocity estimations in clear air mode operations. provide more accurate velocity estimations in clear air mode operations. provide more accurate velocity estimations in clear air mode operations. provide more accurate velocity estimations in clear air mode operations. increase rmax for storms covering a large aerial extent. increase rmax for storms covering a large aerial extent. increase rmax for storms covering a large aerial extent. increase rmax for storms covering a large aerial extent. increase rmax for storms covering a large aerial extent. increase rmax for storms covering a large aerial extent. increase the listening time for the radar. increase the listening time for the radar. increase the listening time for the radar. increase the listening time for the radar. increase the listening time for the radar. increase the listening time for the radar. question #4 of 6 incorrect incorrect. the true target can lie outside the rmax, but dividing by 2 to make it fall within the rmax range makes no sense. continue continue continue continue continue continue incorrect incorrect. the target moves a very small distance between pulses. continue continue continue continue continue continue incorrect incorrect. the speed of light changes only slightly between a vacuum and the atmosphere. continue continue continue continue continue continue incorrect correct! continue continue continue continue continue continue which statement best explains why the target range equation divides by a factor of 2? the time taken for the return pulse to reach the radar includes the round trip time. we only care about the one-way trip time to the target. the time taken for the return pulse to reach the radar includes the round trip time. we only care about the one-way trip time to the target. the time taken for the return pulse to reach the radar includes the round trip time. we only care about the one-way trip time to the target. the time taken for the return pulse to reach the radar includes the round trip time. we only care about the one-way trip time to the target. the time taken for the return pulse to reach the radar includes the round trip time. we only care about the one-way trip time to the target. the time taken for the return pulse to reach the radar includes the round trip time. we only care about the one-way trip time to the target. the speed of light in the atmosphere is roughly half the speed it is in a vacuum. the speed of light in the atmosphere is roughly half the speed it is in a vacuum. the speed of light in the atmosphere is roughly half the speed it is in a vacuum. the speed of light in the atmosphere is roughly half the speed it is in a vacuum. the speed of light in the atmosphere is roughly half the speed it is in a vacuum. the speed of light in the atmosphere is roughly half the speed it is in a vacuum. the target may have moved double the distance by the time the return pulse makes it back to the radar, so dividing by 2 allows for this change in distance. the target may have moved double the distance by the time the return pulse makes it back to the radar, so dividing by 2 allows for this change in distance. the target may have moved double the distance by the time the return pulse makes it back to the radar, so dividing by 2 allows for this change in distance. the target may have moved double the distance by the time the return pulse makes it back to the radar, so dividing by 2 allows for this change in distance. the target may have moved double the distance by the time the return pulse makes it back to the radar, so dividing by 2 allows for this change in distance. the target may have moved double the distance by the time the return pulse makes it back to the radar, so dividing by 2 allows for this change in distance. the return pulse may occur outside the rmax, so dividing by 2 places the target range back within the rmax range where it should be located. the return pulse may occur outside the rmax, so dividing by 2 places the target range back within the rmax range where it should be located. the return pulse may occur outside the rmax, so dividing by 2 places the target range back within the rmax range where it should be located. the return pulse may occur outside the rmax, so dividing by 2 places the target range back within the rmax range where it should be located. the return pulse may occur outside the rmax, so dividing by 2 places the target range back within the rmax range where it should be located. the return pulse may occur outside the rmax, so dividing by 2 places the target range back within the rmax range where it should be located. question #5 of 6 incorrect incorrect. target speed has no bearing on range determination and range folding continue continue continue continue continue continue incorrect incorrect. the second pulse is never sent before it is intended to be sent. continue continue continue continue continue continue incorrect incorrect. decreasing the prf will increase the rmax making it more likely a target will be displayed at the correct range and not closer to the radar. continue continue continue continue continue continue incorrect correct! continue continue continue continue continue continue range folding occurs with the wsr-88d when ________________. the return power from the first pulse arrives at the radar when the second pulse has already been transmitted. the return power from the first pulse arrives at the radar when the second pulse has already been transmitted. the return power from the first pulse arrives at the radar when the second pulse has already been transmitted. the return power from the first pulse arrives at the radar when the second pulse has already been transmitted. the return power from the first pulse arrives at the radar when the second pulse has already been transmitted. the return power from the first pulse arrives at the radar when the second pulse has already been transmitted. the target appears closer to the radar because the radar has decreased the prf. the target appears closer to the radar because the radar has decreased the prf. the target appears closer to the radar because the radar has decreased the prf. the target appears closer to the radar because the radar has decreased the prf. the target appears closer to the radar because the radar has decreased the prf. the target appears closer to the radar because the radar has decreased the prf. the target appears closer to the radar because the radar has decreased the prt. the target appears closer to the radar because the radar has decreased the prt. the target appears closer to the radar because the radar has decreased the prt. the target appears closer to the radar because the radar has decreased the prt. the target appears closer to the radar because the radar has decreased the prt. the target appears closer to the radar because the radar has decreased the prt. the target was moving faster than the maximum unambiguous velocity. the target was moving faster than the maximum unambiguous velocity. the target was moving faster than the maximum unambiguous velocity. the target was moving faster than the maximum unambiguous velocity. the target was moving faster than the maximum unambiguous velocity. the target was moving faster than the maximum unambiguous velocity. question #6 of 6 rac principles roadmap <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Style LeadingMargin="0" FirstLineMargin="0" Justification="Left" ListLevel="1" LineSpacingRule="Multiple" LineSpacing="20" SpacingBefore="0" SpacingAfter="0"> <ListStyle ListType="None" ListTypeFormat="Plain" Start="0" Color="#000000,00" BulletChar="•" BulletFont="Arial"> <BulletPicture Size="0x0" /> </ListStyle> </Style> <Span Text="Welcome to the Radar & Applications Course (RAC) Principles of Doppler Weather Radar. This lesson is on Transmitting and Receiving Characteristics of the WSR-88D radar. Let’s get started!"> <Style FontFamily="Open Sans" FontSize="11" FontIsBold="False" FontIsItalic="False" FontIsUnderline="False" FontIsStrikeout="False" ForegroundColor="dk1,00" Elevation="Normal" DisplayCase="AsIs" LinkColor="dk1,00" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Style LeadingMargin="0" FirstLineMargin="0" Justification="Left" ListLevel="1" LineSpacingRule="Multiple" LineSpacing="20" SpacingBefore="4.31999969" SpacingAfter="0"> <ListStyle ListType="None" ListTypeFormat="Plain" Start="0" Color="#000000,00" BulletChar="•" BulletFont="Arial"> <BulletPicture Size="0x0" /> </ListStyle> </Style> <Span Text="Here is the complete roadmap for the entire “Principles of Doppler Weather Radar” topic of RAC. You are currently in the Radar Fundamentals section of that topic."> <Style FontFamily="Open Sans" FontSize="11" FontIsBold="False" FontIsItalic="False" FontIsUnderline="False" FontIsStrikeout="False" ForegroundColor="#444444" Elevation="Normal" DisplayCase="AsIs" LinkColor="#444444" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="Here are the learning objectives for this lesson. Please take a moment to review these objectives, as the quiz at the end of this lesson is based on these objectives."> <Style FontSize="11" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Style /> <Span Text="In the first lesson of this section, we learned that the WSR-88D emits pulsed radiation so that it can determine range to target. Accurate range detection depends on the transmitting and receiving characteristics of the radar. The WSR-88D also measures velocity which has a similar dependence on those characteristics. This lesson will discuss how range and velocity information are impacted by the radar’s transmitting and receiving characteristics and describe what these key characteristics are."> <Style FontSize="11" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="One key transmitting characteristic is pulse repetition frequency (PRF). The PRF determines the number of pulses sent out by the radar every second. The WSR-88D can assign one of eight different PRFs to a pulse depending on the waveform in use. This slide shows a table with a sample set of PRFs that could be implemented. We will explain why the PRF matters in a bit."> <Style FontSize="11" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="Another way to look at the PRF is the Pulse Repetition Time (PRT). PRT tell you how much time elapses between two consecutive pulses and is simply the reciprocal of the PRF. For the eight PRF options shown on the last slide, we provide their PRTs in this table. PRTs are very short!"> <Style FontSize="11" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="As the WSR-88D emits radiation to determine the range to targets, one might ask if there’s a range limit to this process. There is! The maximum unambiguous range (or R"> <Style FontSize="11" /> </Span> <Span Text="max"> <Style FontSize="11" Elevation="Subscript" /> </Span> <Span Text=") tells you how far the first pulse travels out and back before the next pulse is transmitted. We determine R"> <Style FontSize="11" /> </Span> <Span Text="max"> <Style FontSize="11" Elevation="Subscript" /> </Span> <Span Text=" by taking the speed of light (c) and divide it by two times the PRF. We use two times the PRF because the pulse must travel there and back again. This relationship tells us that the maximum unambiguous range is inversely proportional to PRF. In other words, as the radar sends out more frequent pulses, R"> <Style FontSize="11" /> </Span> <Span Text="max"> <Style FontSize="11" Elevation="Subscript" /> </Span> <Span Text=" decreases and vice versa."> <Style FontSize="11" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="When it comes to measuring velocity, the radar measures the phase shift between pulses through a technique called pulse-pair processing. This technique uses the difference in phase of the return signal from one pulse to the next. A target's phase will change from pulse to pulse because the target intercepts the transmitted wave at a different phase position along the wave. However, if the target moves too fast, the resulting phase difference leads to an ambiguous velocity. For a given sampling rate, the speed limit where this ambiguity is reached is called the Nyquist Velocity, maximum unambiguous velocity, or V"> <Style FontSize="11" /> </Span> <Span Text="max"> <Style FontSize="11" Elevation="Subscript" /> </Span> <Span Text=". How do we get around this ambiguity? If the radar PRF increases, then scatters don’t move as far between pulses which makes ambiguity less likely. So, the higher the PRF, the higher the V"> <Style FontSize="11" /> </Span> <Span Text="max"> <Style FontSize="11" Elevation="Subscript" /> </Span> <Span Text="."> <Style FontSize="11" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="At this point, you might think we have a dilemma. You’re right we do…the Doppler dilemma! Lower PRFs give us better range detection and higher PRFs reduce velocity ambiguities. It feels like we have to choose one option or the other, hence the dilemma. Fortunately, radar engineers devised a work around when developing scanning strategies for the WSR-88D. We will discuss how scanning strategies can help maximize both R"> <Style FontSize="11" /> </Span> <Span Text="max"> <Style FontSize="11" Elevation="Subscript" /> </Span> <Span Text=" and V"> <Style FontSize="11" /> </Span> <Span Text="max"> <Style FontSize="11" Elevation="Subscript" /> </Span> <Span Text=" in a later lesson. For now, you just need to know that PRF has opposite impacts on R"> <Style FontSize="11" /> </Span> <Span Text="max"> <Style FontSize="11" Elevation="Subscript" /> </Span> <Span Text=" and V"> <Style FontSize="11" /> </Span> <Span Text="max"> <Style FontSize="11" Elevation="Subscript" /> </Span> <Span Text=".
"> <Style FontSize="11" /> </Span> </Block> <Block> <Span Text=""> <Style FontSize="11" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Style /> <Span Text=" So, I spent the last several slides talking about Pulse Repetition Frequency and Time, Maximum Unambiguous Range and Velocity, and the Doppler Dilemma. You may ask yourself, “Why did you put me through that Andy?” Well, these concepts have a significant impact on the radar products you analyze. On Reflectivity products, these concepts help us ensure that the returns you see on a radar display are actually located at the range where the data say they are. We’ll explain that application on the next several slides. On Velocity products, they also help explain that “purple haze” we see on products and why it’s very difficult to eliminate it without concessions in other areas. We’ll discuss the details of that in a later lesson."> <Style FontSize="11" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="When the pulse returns to the radar, we want to know how far away the echo that reflected the signal was. We can determine the range from our knowledge of the pulse’s speed and how long it has been since the pulse was transmitted. If we multiple those two together and divide by two (because the pulse travels there and back again), we get the target’s range. "> <Style FontSize="11" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Style /> <Span Text="Pulse duration represents another important transmitting characteristic. It is simply the length of time the radar spends transmitting a pulse. As pulse duration increases, the pulse’s power density (and generally its sensitivity) increases. The WSR-88D incorporates two pulse duration modes: short pulse mode and long pulse mode. Short pulses transmit for 1.57 microseconds, and long pulses transmit for 4.7 microseconds. Only VCP 31 uses a long pulse to provide more sensitivity during clear air mode. The other VCPs use a short pulse for reasons we will explain on the next slide.
"> <Style FontSize="11" /> </Span> </Block> <Block> <Style /> <Span Text=""> <Style FontSize="11" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="Now that you know the target range equation, let’s talk about range folding. As long as the first pulse makes it back to the radar before the second pulse is transmitted, the radar will correctly measure the range to the target. If the returned pulse arrives after the second pulse is transmitted, the radar will think the data was from the latest pulse, not the first one. The radar will then place the echo closer to the radar than it actually is. This phenomenon is called range folding."> <Style FontSize="11" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="This first example shows the normal case where no range folding will occur. The radar sends out the pulse, encounters a target before the maximum unambiguous range (also known as the first trip), and returns an echo to the radar. The returned pulse arrives at the radar before the second pulse is transmitted and therefore gets the correct range applied to it. "> <Style FontSize="11" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="Radars can transmit and listen, but not at the same time. Therefore, longer pulse durations mean less listening for radar echo returns. The listening period refers to the period of time not transmitting a pulse. Specifically, the listening period starts when the first pulse stops transmitting and ends when the second pulse starts. The WSR-88D listens in short pulse mode 99.8% of the time and 99.5% of the time in long pulse mode. In either mode, the radar is a very good listener. However, that small difference between short and long pulse modes does have a significant impact on velocity estimates. Velocity estimates are less reliable in long pulse mode. That’s why long pulse mode is only used in one volume coverage pattern."> <Style FontSize="11" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="In this second example, the target lies outside the maximum unambiguous range. When the first pulse encounters the target, the target returns some of the power back towards the radar. However, before that energy can return, a second pulse is transmitted. When the first pulse makes it back to the radar, the radar thinks this power return is from the second pulse, not the first one. Therefore, the radar places the target at a closer range than where it actually resides. It is range folded. 
"> <Style FontSize="11" /> </Span> </Block> <Block> <Span Text="
"> <Style FontSize="11" /> </Span> </Block> <Block> <Span Text="Remember our earlier conversation about how the pulse repetition frequency, or PRF, affected max range? A lower PRF would result in a farther max range since the pulse would have more time to return before a new one is sent. In this way, adjusting the PRF used by the radar can make range folding less of a problem. Remember, though, that there is a cost. Using a lower PRF does result in a lower maximum ambiguous velocity, thanks to the Doppler Dilemma."> <Style FontSize="11" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="In summary, we discussed how certain transmitting and receiving characteristics of the WSR-88D radar pulse impact the range and velocity estimates we can accurately measure. When transmitting the radar pulse, the pulse repetition frequency and time help determine both the maximum unambiguous range and velocity that can be measured. This relationship leads to the Doppler dilemma. The WSR-88D applies different scanning strategies to address this conundrum.
"> <Style FontSize="11" /> </Span> </Block> <Block> <Span Text="
"> <Style FontSize="11" /> </Span> </Block> <Block> <Span Text="When receiving the radar pulse, the pulse duration becomes significant. This time is related to the maximum unambiguous range and the potential for range folded data. When targets are located beyond that Rmax for a particular PRF, those targets will appear closer to the radar then they actual are. Fortunately, the WSR-88D uses a combination of scanning strategies and algorithms to unfold these data in many situations, but certainly not all. 
"> <Style FontSize="11" /> </Span> </Block> <Block> <Span Text="
"> <Style FontSize="11" /> </Span> </Block> <Block> <Span Text="When you are ready, click the next button to start the quiz."> <Style FontSize="11" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Style /> <Span Text="Thank you for completing this lesson. Click the Exit button to complete the lesson, and proceed on to the next lesson in the topic."> <Style FontSize="11" /> </Span> </Block> </Content> </Document>