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SUBMIT ALL submit all SUBMIT submit Submit Unmute Autoscroll Close Transcript Move window Open Resize window Resume autoscroll Select track Show timestamps Transcripts Options volume principles of radar wsr-88d base data quality lesson scope this lesson will not cover all known data quality issues in detail. wsr-88d base data quality homepage reflectivity reflectivity reflectivity reflectivity velocity velocity velocity velocity dual-pol dual-pol dual-pol dual-pol dq mitigation dq mitigation dq mitigation dq mitigation summary & quiz summary & quiz summary & quiz summary & quiz other dq resources other dq resources other dq resources other dq resources artifacts 1 2 3 4 reflectivity artifacts electromagnetic interference electromagnetic interference electromagnetic interference electromagnetic interference artificial discontinuities artificial discontinuities artificial discontinuities artificial discontinuities clutter mitigation issues clutter mitigation issues clutter mitigation issues clutter mitigation issues biological returns biological returns biological returns biological returns chaff chaff chaff chaff reflections reflections reflections reflections when you’ve visited all 6 buttons click next to go back to the homepage bistatic coupling interference from 4g tower sun spike electromagnetic interference sun spikes sun spikes sun spikes sun spikes anthropogenic sources anthropogenic sources anthropogenic sources anthropogenic sources bistatic coupling bistatic coupling bistatic coupling bistatic coupling i-90 traffic terrain spikes artificial discontinuities start of elevation start of elevation start of elevation start of elevation terrain spikes terrain spikes terrain spikes terrain spikes terrain clutter false negative: miss clutter where it is present most likely with weak returns or during fast scans with fewer pulses/radial false positive: misidentify clutter where it isn’t present clutter mitigation issues false positives false positives false positives false positives clutter mitigation detection (cmd) algorithm false negatives false negatives false negatives false negatives birds take flight 1128z 1138z 1148z 1158z 1208z 1959z 2001z 2003z 2004z 2006z biological returns common common common common uncommon uncommon uncommon uncommon chaff radar countermeasure used by military aircraft reflections 2116z 2119z 2122z 2129z rf ring 0030z 0032z 0035z 0037z 0039z 0042z 0044z 0046z 0049z 0051z velocity artifacts velocity dealiasing errors velocity dealiasing errors velocity dealiasing errors velocity dealiasing errors range folding mitigation range folding mitigation range folding mitigation range folding mitigation sidelobe velocity contamination sidelobe velocity contamination sidelobe velocity contamination sidelobe velocity contamination dual-pol artifacts differential attenuation differential attenuation differential attenuation differential attenuation non-uniform beam filling non-uniform beam filling non-uniform beam filling non-uniform beam filling depolarization streaks depolarization streaks depolarization streaks depolarization streaks differential reflectivity wedges differential reflectivity wedges differential reflectivity wedges differential reflectivity wedges differential phase wrapping differential phase wrapping differential phase wrapping differential phase wrapping wet radome effect wet radome effect wet radome effect wet radome effect zdr z rda rda when the horizontal (typically) or vertical channel attenuates more than the other rda lower reflectivity values down radial from a strong precip core power reduction of radar pulse as it travels through the atmosphere the more heavy rain/hail, the more attenuation that will occur differential attenuation attenuation attenuation attenuation attenuation reflectivity example reflectivity example reflectivity example reflectivity example differential attenuation differential attenuation differential attenuation differential attenuation cc dpr hca impacts cascade from base data to derived products cc z impacts seen primarily in correlation coefficient base data non-uniform beam filling δφdp ~ small δφdp ~ large results in corrupted φdp and cc data down radial from affected area mixed beam filling results in primarily dual-pol base data being impacted results in underestimated reflectivity values partial beam filling radar equation assumes all liquid, uniformly filled radar beam uniform beam filling non-uniform beam filling uniform beam filling uniform beam filling uniform beam filling uniform beam filling partial beam filling partial beam filling partial beam filling partial beam filling mixed beam filling mixed beam filling mixed beam filling mixed beam filling nbf nbf nbf nbf nbf example nbf example nbf example nbf example other products other products other products other products z zdr visible in zdr, usually on higher elevation tilts (streaks can be higher or lower in value) initial polarized signal cross- polarized signal electrically aligned ice crystals lead to cross-polarization of dual-pol pulse, contaminating down radial zdr values note: pulse contamination can occur in either direction depolarization streaks what are they? what are they? what are they? what are they? example example example example differential reflectivity wedges 1959z 2001z 2003z 2004z 2006z 2008z notice increase in zdr as line moves over rda zdr decreases as the line passes through notice z drop in stratiform area as the line passes z increases again as the line moves east 1959z 2001z 2003z 2004z 2006z 2008z wet radome effect z z z z zdr zdr zdr zdr differential phase wrapping isdp ~ 60° isdp ~ 0° wrapped φdp values impact dual-pol data data quality mitigation antenna rotation antenna rotation antenna rotation antenna rotation clutter detection clutter detection clutter detection clutter detection differential attenuation and nbf differential attenuation and nbf differential attenuation and nbf differential attenuation and nbf dq dashboard dq dashboard dq dashboard dq dashboard using differential phase using differential phase using differential phase using differential phase antenna rotation general surveillance severe convection clutter detection false positive detection: false negative detection: option 1: all bins clutter sector option 2: exclusion zone use the best vcp for the current weather situation differential attenuation and nbf differential attenuation –> zdr non-uniform beam filling –> cc hydroclassification dual-pol precip products adjust qpes using differential phase 60° if the calibration is routinely outside of these limits, your office should contact the roc hotline for help. dq dashboard shade charts shade charts shade charts shade charts shift change checklist shift change checklist shift change checklist shift change checklist click on this gauge! click to see an example click to see an example click to see an example click to see an example click to see an example click to see an example click to see an example click to see an example subscribe to the forum on vlab contact info: https://www.roc.noaa.gov/branches/operations-branch/wsr88d-hotline-links-info.php email: nws.wdtd.rachelp@noaa.gov web: https://training.weather.gov/wdtd/ contact wdtd staff directly via noaa emails other dq resources for the nws wdtd wdtd wdtd wdtd roc hotline roc hotline roc hotline roc hotline wsr-88d email forum wsr-88d email forum wsr-88d email forum wsr-88d email forum shift change checklist shift change checklist shift change checklist shift change checklist summary data artifacts seen in reflectivity, velocity, and dual-pol general ways to mitigate potential data quality issues other dq resources available to you & your office incorrect that is incorrect. please try again. try again try again try again try again try again try again incorrect you did not select the correct response. continue continue continue continue continue continue correct that's right! you selected the correct response. continue continue continue continue continue continue melting hail in the radar beam melting hail in the radar beam melting hail in the radar beam melting hail in the radar beam melting hail in the radar beam melting hail in the radar beam canting of ice crystals due to electrification canting of ice crystals due to electrification canting of ice crystals due to electrification canting of ice crystals due to electrification canting of ice crystals due to electrification canting of ice crystals due to electrification heavy precipitation aligned along a radial heavy precipitation aligned along a radial heavy precipitation aligned along a radial heavy precipitation aligned along a radial heavy precipitation aligned along a radial heavy precipitation aligned along a radial incorrect initial system differential phase incorrect initial system differential phase incorrect initial system differential phase incorrect initial system differential phase incorrect initial system differential phase incorrect initial system differential phase depolarization streaks result from which of the following conditions? incorrect that is incorrect. please try again. try again try again try again try again try again try again incorrect you did not select the correct response. continue continue continue continue continue continue correct that's right! you selected the correct response. continue continue continue continue continue continue differential reflectivity differential reflectivity differential reflectivity differential reflectivity differential reflectivity differential reflectivity correlation coefficient correlation coefficient correlation coefficient correlation coefficient correlation coefficient correlation coefficient differential phase differential phase differential phase differential phase differential phase differential phase specific differential phase specific differential phase specific differential phase specific differential phase specific differential phase specific differential phase which base data product was specifically identified as an aid to mitigate radar data quality issues? incorrect that is incorrect. please try again. try again try again try again try again try again try again incorrect you did not select the correct response. continue continue continue continue continue continue correct that's right! you selected the correct response. continue continue continue continue continue continue click on the area in the graphic where you observe interference. incorrect that is incorrect. please try again. try again try again try again try again try again try again incorrect you did not select the correct response. continue continue continue continue continue continue correct that's right! you selected the correct response. continue continue continue continue continue continue range folding mitigation artifacts range folding mitigation artifacts range folding mitigation artifacts range folding mitigation artifacts range folding mitigation artifacts range folding mitigation artifacts velocity dealiasing errors velocity dealiasing errors velocity dealiasing errors velocity dealiasing errors velocity dealiasing errors velocity dealiasing errors differential phase wrapping differential phase wrapping differential phase wrapping differential phase wrapping differential phase wrapping differential phase wrapping wet radome effect wet radome effect wet radome effect wet radome effect wet radome effect wet radome effect velocity wedges velocity wedges velocity wedges velocity wedges velocity wedges velocity wedges which of the following were identified as common base velocity data quality artifacts (select all that apply)? incorrect that is incorrect. please try again. try again try again try again try again try again try again incorrect you did not select the correct response. continue continue continue continue continue continue correct that's right! you selected the correct response. continue continue continue continue continue continue use the available vcps in situations for which they were designed use the available vcps in situations for which they were designed use the available vcps in situations for which they were designed use the available vcps in situations for which they were designed use the available vcps in situations for which they were designed use the available vcps in situations for which they were designed use differential reflectivity to check initial system differential phase values use differential reflectivity to check initial system differential phase values use differential reflectivity to check initial system differential phase values use differential reflectivity to check initial system differential phase values use differential reflectivity to check initial system differential phase values use differential reflectivity to check initial system differential phase values monitor correlation coefficient data for signs of differential attenuation monitor correlation coefficient data for signs of differential attenuation monitor correlation coefficient data for signs of differential attenuation monitor correlation coefficient data for signs of differential attenuation monitor correlation coefficient data for signs of differential attenuation monitor correlation coefficient data for signs of differential attenuation use all bins clutter suppression to ensure any and all clutter is removed from the data use all bins clutter suppression to ensure any and all clutter is removed from the data use all bins clutter suppression to ensure any and all clutter is removed from the data use all bins clutter suppression to ensure any and all clutter is removed from the data use all bins clutter suppression to ensure any and all clutter is removed from the data use all bins clutter suppression to ensure any and all clutter is removed from the data which of the following is a general practice forecasters can apply to get the best data quality possible? incorrect that is incorrect. please try again. try again try again try again try again try again try again incorrect you did not select the correct response. continue continue continue continue continue continue correct that's right! you selected the correct response. continue continue continue continue continue continue ground targets blocking the vertical signal more than the horizontal ground targets blocking the vertical signal more than the horizontal ground targets blocking the vertical signal more than the horizontal ground targets blocking the vertical signal more than the horizontal ground targets blocking the vertical signal more than the horizontal ground targets blocking the vertical signal more than the horizontal ground targets causing a gradient in the differential phase across the beam ground targets causing a gradient in the differential phase across the beam ground targets causing a gradient in the differential phase across the beam ground targets causing a gradient in the differential phase across the beam ground targets causing a gradient in the differential phase across the beam ground targets causing a gradient in the differential phase across the beam non-uniform beam filling non-uniform beam filling non-uniform beam filling non-uniform beam filling non-uniform beam filling non-uniform beam filling clutter detection and removal issues clutter detection and removal issues clutter detection and removal issues clutter detection and removal issues clutter detection and removal issues clutter detection and removal issues wedges in differential reflectivity can occur because of: incorrect that is incorrect. please try again. try again try again try again try again try again try again incorrect you did not select the correct response. continue continue continue continue continue continue correct that's right! you selected the correct response. continue continue continue continue continue continue click on the location in the image on the right that shows evidence of non-uniform beam filling. incorrect that is incorrect. please try again. try again try again try again try again try again try again incorrect you did not select the correct response. continue continue continue continue continue continue correct that's right! you selected the correct response. continue continue continue continue continue continue ground clutter detected where it is not actually present ground clutter detected where it is not actually present ground clutter detected where it is not actually present ground clutter detected where it is not actually present ground clutter detected where it is not actually present ground clutter detected where it is not actually present ground clutter is not detected where it is actually present ground clutter is not detected where it is actually present ground clutter is not detected where it is actually present ground clutter is not detected where it is actually present ground clutter is not detected where it is actually present ground clutter is not detected where it is actually present weather signals present in the base data are included when they should not be weather signals present in the base data are included when they should not be weather signals present in the base data are included when they should not be weather signals present in the base data are included when they should not be weather signals present in the base data are included when they should not be weather signals present in the base data are included when they should not be radial velocity data are set to zero when the original data should be included radial velocity data are set to zero when the original data should be included radial velocity data are set to zero when the original data should be included radial velocity data are set to zero when the original data should be included radial velocity data are set to zero when the original data should be included radial velocity data are set to zero when the original data should be included what is meant by a “false positive” detection in the cmd algorithm? alyssa.woodward@noaa.gov acknowledgments: andy wood <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Style /> <Span Text="Hello everyone. My name is Alyssa and I will be your instructor for this lesson in the Principles of Radar topic in RAC titled “WSR-88D Base Data Quality.”"> <Style FontSize="12" /> </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="If you are completing this course for credit please review this interaction on how to complete this course within the National Weather Service Commerce Learning Center. After viewing all the slides click “next” to continue."> <Style FontSize="12" /> </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="Before we move on let’s take a moment to discuss the scope of this lesson. There are dozens of known base data quality anomalies from the WSR-88D that have been documented in some form over the last 25 years. We will not cover all of them here. Some of these data artifacts, such as side lobe contamination, have already been discussed multiple times in previous lessons. So, we will let that content stand for itself. Other anomalies will either be discussed in subsequent lessons, happen too infrequently to document and discuss properly, or were simply cut for the sake of time. "> <Style FontSize="12" /> </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="Welcome to the homepage of this module. Click on the six blue buttons in numerical order to learn more about each section. First, this lesson will discuss reflectivity, velocity, and dual-pol artifacts. Then, this lesson will discuss data quality mitigation and other data quality resources for the NWS. And finally you will end with the summary and quiz."> <Style FontSize="12" /> </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 this first section we will discuss some common data quality issues that impact base reflectivity. Click on one of the blue buttons to get started. Once you have visited all six buttons click next to go back to the homepage."> <Style FontSize="12" /> </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="Electromagnetic interference occurs when an external source of electromagnetic energy interferes with the radar’s data collection design. The source of electromagnetic interference can be from any number of things. Click on the blue buttons to the left to see different examples of this.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Sun Spikes"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": One common form of electromagnetic interference is a sun spike. These show up on the radar before sunset or after sunrise, when the sun just happens to be at the same elevation that the radar is scanning. Sun spikes occur at predictable times, so their impacts tend to be minimal.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Anthropogenic Sources"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": Frequencies near S-band are in high demand for telecommunications and other applications. So, another form of electromagnetic interference you may see is interference from 4G comms towers and other private industry sources. This interference can be transient or persist for several volume scans. If the interference persists, work with the Radar Operations Center to identify the point source location and work with the owner to fix the issue.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Bistatic Coupling"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": Sometimes the interference isn’t from an external source at all. Bistatic coupling occurs when two nearby WSR-88D sites have similar transmitter frequencies and favorable atmospheric conditions are present. Their antennas are able to detect the other site’s transmitted pulse. This type of interference, like in the example shown, may also be called running rabbits. This interference requires the transmitted pulse to be ducted or super-refracted in a way that it will travel an atypical path to the nearby radar.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text=""> <Style FontSize="12" /> </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="Occasionally, radial discontinuities may be apparent in the base data. Click the buttons on the left to see a couple of examples of these discontinuities and where and when you might see them.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Start of Elevation"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": Occasionally, the 0.5 tilt will have a noticeable discontinuity at the beginning of the scan. Many things can cause this discontinuity. Sometimes the radar antenna has a wobble as it starts the 0.5 Contiguous Surveillance scan that goes away after a few radials. If the wobble occurs frequently or throughout the scan, it can signal an issue with the radar. I should note that if the same discontinuity is seen in the Contiguous Doppler cut, it’s not due to the start of the volume scan. Similar artifacts can be seen during super refractive conditions or at sites near significant bodies of water.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Terrain Spikes"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": Radials of higher reflectivity may be visible across hills or mountains. These spikes exist regardless of the form of clutter filtering used. Sometimes the data artifact will look like a large cluster of echoes instead of a series of spikes. The spikes may be more apparent when you switch to other base products like velocity. Weather signals do not appear to be impacted when these artifacts are present, and no known fix is available for them. However, you should talk with your radar focal point and electronics tech if you notice this issue frequently or for a long duration.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text=""> <Style FontSize="12" /> </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="The Clutter Mitigation Detection (or CMD) algorithm is the preferred means for the WSR-88D to identify range bins contaminated with ground clutter. However, the algorithm is not perfect. CMD can fail and impact base data quality in two ways: It can misidentify clutter where it isn’t present, aka false positives, or it can miss clutter where it is present, aka false negatives. This section will discuss the ramifications of both situations.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="False Positives"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": The CMD algorithm uses multiple inputs to identify clutter. It performs best when a strong return signal exists and there are lots of pulses per radial. When the radar detects weak returns (such as weak stratiform precipitation) using a faster VCP (with fewer pulses per radial), performance issues can occur. One way the algorithm can perform poorly is by falsely identifying clutter in a given bin. These false positive detections can result in noisy data with sporadic gates of signal removed that didn’t contain clutter. This issue can impact convective storms such as in the example shown. See how several bins appear to be missing data in this area of high reflectivity? Anytime severe convection is anticipated, the need for VCP 12 or 212 outweighs the desire for perfect clutter suppression. However, using VCP 215 during stratiform events will improve CMD performance.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="False Negatives"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": A similar problem happens when the clutter algorithms fail to detect clutter. In the example shown, some of the clutter from terrain has been identified and removed, but not all of it. These artifacts often occur because some aspect of the return doesn’t look like clutter. See, if I pull up the bypass map data for this area, you can see some form of clutter filtering occurring. So, it’s not like the CMD algorithm didn’t detect clutter. Often the problem occurs because the velocities associated with the clutter have a significant non-zero component. To address this issue, radar operators can add sectors for all bins filtering or create an exclusion zone for the routine clutter areas like this one. These options are both preferable to turning off the CMD algorithm and relying on all bins clutter suppression throughout the entire scan.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text=""> <Style FontSize="12" /> </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="Click on the two blue buttons on the left to see an example of common and uncommon biological returns.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Common"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": Biological returns can appear in many different ways, depending on whether the returns are from birds, bats, insects, or something else. This example shows a loop of bats leaving their caves around sunset. In this case, you see various values of CC and ZDR depending on where you look in the returns because of the viewing angle of bats relative to the radar beam. The orientation of the biological targets strongly influence the dual-pol variables in these kinds of returns. Bats can be seen often in known areas around sunset, while birds are often visible taking off around sunrise. Migratory birds and seasonal insects can also be regularly seen in radar data when you know what and when to look.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Uncommon"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": Now lets look at a less common (or predictable) instance of biological returns. In this case, a 4.3 magnitude earthquake struck about 90 to 120 minutes before sunrise. On the image immediately following the earthquake, which was at 1139 Z, you can see a significant area of returns appear in the circled area at 1148 Z. In the scans after that one, you can see the returns decrease as the startled birds settle back down again after the earthquake. In this case, the radar was in clear air mode so we didn't observe the sequence as well as we did with the common case.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text=""> <Style FontSize="12" /> </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="Just in case you are not familiar with the subject, military aircraft use small, metallic pieces called chaff as a radar countermeasure against enemy aircraft. Chaff reflects the radar pulse very well, by design, and can be visible for prolonged periods of time in 88D products. In this example, the radar collected data in clear air mode so the chaff can’t be confused with any precipitation. However, notice how the CC values in the echo are very low, clearly indicating the returns are not meteorological. ZDR values are mostly highly positive, which is typical for chaff cases."> <Style FontSize="12" /> </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="Another data artifact you might observe is reflections of echoes off of buildings and other ground clutter. What happens is the radar pulse reflects off of some clutter, gets directed in a different direction towards a precipitation echo, gets reflected back to the ground clutter, and ultimately back to the radar. In this example, you can see a spike in the 2122 Z data annotated with a white arrow that appears to be caused by a multi-story hospital located at the location marked by the yellow star. The data can look similar to interference except for a couple of key differences. First, the reflection is usually only visible for a brief period of time while the atmospheric conditions are just right along with the proper alignment between the ground clutter reflector and target precipitation. The second difference is that the radar data should contain values more comparable to precipitation (such as higher CC values) than what you would typically see in interference."> <Style FontSize="12" /> </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 this next section we will discuss some common data quality issues that impact base velocity. Click on the three blue buttons to learn more about them.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Velocity Dealiasing Errors"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": A whole lesson discusses velocity dealiasing and how it works, so a lot could be said and shown on this subject. Even with the velocity dealiasing algorithms in place at the RPG, sometimes errors occur. VCP 31 is most susceptible to dealiasing errors because of its low Nyquist Velocity. However, all VCPs can potentially be impacted. If you suspect velocities may be improperly dealiased, check for temporal and vertical continuity of the signature as dealiasing errors tend to be transient in nature. Try this example. Use the slider to look at the various scans so you can get a sense of how the dealiasing changes as time goes on.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Range Folding Mitigation"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": At this point, you have likely taken the lesson on range unfolding of velocity data. So, you should realize that range folded velocity data happens. That’s just life. However, RF data happens more frequently in certain situations. For instance, range gates just beyond the first trip (or Rmax distance) are often impacted by range folded velocities. Even when you use a SZ-2 VCP, you will likely get a ring of RF data at the end of the first trip distance of the Contiguous Surveillance or Doppler scans. While you can mitigate this issue to a degree by changing to VCP 12, you will often end up with more RF data that way. So, you just need to pick your poison in these situations.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Sidelobe Velocity Contamination"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": A third form of common velocity data artifacts involve velocity contamination due to elevation sidelobes. This data artifact has been around for quite some time, but has grown in visibility over the last few years. As a result, we have added a standalone lesson in RAC to address this topic. We will discuss the details further in that lesson. We just mention it here for forecaster awareness.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text=""> <Style FontSize="12" /> </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="There are numerous dual-pol related data quality issues that can be visible on radar products. This section will focus on six of these artifacts that impact dual-pol base data: differential attenuation, non-uniform beam filling, depolarization streaks, differential reflectivity wedges, differential phase wrapping, and wet radome effect. Click on each of these buttons."> <Style FontSize="12" /> </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="Click on each of the three blue buttons to learn more about differential attenuation.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Attenuation"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": Attenuation of the radar pulse has always been an issue with weather radar. Anytime electromagnetic energy is transmitted through a medium, some of the energy will be attenuated. The more dense the medium, such as a volume of heavy rain or hail, the more attenuation will occur. The attenuated portion of the radar pulse is lost and cannot be recovered. Fortunately, the WSR-88D transmits a 10 cm wavelength pulse, which attenuates much less than shorter wavelength radar.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Reflectivity Example"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": Attenuation impacts reflectivity more than products like velocity and spectrum width because it reduces the power in the radar pulse. What does a reflectivity product look like when it has been negatively impacted by attenuation? Take a look at the reflectivity example on the slide. This squall line is oriented directly along a radial. This line should help you visualize the radial orientation better. See how the reflectivity values are significantly lower down radial from the storm core compared to other nearby radials? That difference is due to attenuation.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Differential Attenuation"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": So, what is differential attenuation? Well differential attenuation occurs when one component of the polarized pulse’s signal, usually the horizontal channel, gets attenuated more than the other. I’ve added the differential reflectivity product from the same time as the previous example to demonstrate. I have highlighted the area in base reflectivity that appears to be attenuated. The same region appears to be experiencing differential attenuation as well. In fact, if I move the area from ZDR over to Z, you can see the attenuation in the horizontal channel is noticeably closer to the RDA in ZDR than it is in Z. Any products derived from this ZDR data will inaccurately represent the actual atmospheric conditions.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="
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"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text=""> <Style FontSize="12" /> </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="Click on the six blue buttons to learn more."> <Style FontSize="12" /> </Span> <Span Text="Uniform Beam Filling"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": Before we discuss non-uniform beam filling, we need to provide some context as to why that condition is significant. Remember that the Probert-Jones radar equation assumes that the radar beam is filled uniformly with liquid precipitation. In reality, both of those conditions are frequently not met. So, what are the impacts when that happens?
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Partial Beam Filling"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": The beam only being partially filled with precipitation results in underestimated reflectivity values. Differential reflectivity usually isn’t impacted because it relies on the ratio between the two channels which are often impacted comparably by partial beam filling.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Mixed Beam Filling"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": When the beam is filled with a mixture of hydrometeor sizes and types, the Probert-Jones uniformity assumption isn’t necessarily violated. After all, as long as the different sizes are uniformly distributed throughout the beam, the assumption is still valid. However, that mixture of hydrometeors still impacts the base data. The dual-pol data, in particular, are more noticeably impacted than the legacy base products.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="NBF"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": While both partial and mixed beam filling can impact your base data, non-uniform beam filling differs from both of these situations in that it creates artifacts in the data that impact both the radar bins in question, but all bins down radial from that bin as well. The problem is related to the combination of mixed precipitation types that are not uniformly distributed. At the top of the beam, differential phase changes marginally because the hail stones dominate the returned power. At the bottom of the beam, differential phase changes significantly because it is passing through all liquid precipitation. This configuration results in a PhiDP gradient across the beam that continues to propagate with the pulse down the radial. This situation results in lower correlation coefficient values from there on out than what actually exists in the atmosphere.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="NBF Example"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": So, what does a correlation coefficient product look like when it has been impacted by non-uniform beam filling? Here’s an example. The circled area in the reflectivity and CC products shows where the non-uniform beam filling is actually occurring. Notice how the down radial CC values are significantly lower than the values from nearby radials. We don’t see a similar artifact in the reflectivity data.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Other Products"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": So, how does this data artifact impact other products? Well, the easiest way to see the impact is by looking at the dual-pol precipitation products. The low CC values cause a large swatch of bins to be classified as biological targets that are actually precipitation. When this information gets used to generate the instantaneous rate product, the bins labeled as biological returns have no accumulated precipitation. So, you can see how this artifact can be a problem and why forecasters need to be mindful of these signatures in the base data.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="
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"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text=""> <Style FontSize="12" /> </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="Click on the two blue buttons to learn what depolarization streaks are and an example of them.
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"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="What are they?"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": Depolarization streaks occur along a radial when the pulse passes through an electrified region of a storm populated with ice crystals. The electric field in the storm, if it’s strong enough, can cause the ice crystals to cant in a preferred direction. When the radar pulse hits these canted crystals, some of the energy in the radar pulse cross-polarizes. So, you start off with an initial polarized signal that is equally strong in both the vertical and horizontal. After passing through the electrified area, one of the orthogonal components is stronger than the other, contaminating the down radial ZDR values.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Example"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": So, what do these depolarization streaks look like in the base radar data? You can see that base reflectivity really isn’t impacted at all. However, in ZDR you can see streaks of higher or lower values when compared to adjacent radials. These streaks will be transient in nature as the electric field fluctuates. They will be more noticeable on higher elevation tilts where ice crystals are more likely in convection. The good news, these data artifacts have minimal impacts to operations. But, it’s still good to know what they are so that you can recognize them.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text=""> <Style FontSize="12" /> </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="Occasionally, wedges (or spikes) will appear in differential reflectivity data. These artifacts can appear for several different reasons. In some cases, like this example, there may be some ground object that blocks more of the vertical pulse than the horizontal pulse. The clear air returns are so highly positive that the wedge isn’t apparent there. However, once you enter into weather returns, you can see the values are out of whack. Sometimes, ZDR wedges can be due to hardware issues, so you want to tell your radar focal point or electronic tech about these kinds of signatures when you notice them."> <Style FontSize="12" /> </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="Click on the two buttons to learn more.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Z"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": When precipitation falls on the radome, reflectivity data may experience some subtle attenuation effects where values dip. Use the slider bar to see how reflectivity is impacted as this line moves over the radome.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="ZDR"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": This artifact often appears more clearly in differential reflectivity, although the values tend to increase when the radome is wet. Use the slider bar to see how a wet radome effect impacts ZDR.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="
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"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text=""> <Style FontSize="12" /> </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="We don’t spend a whole lot of time in the RAC on differential phase (or phi), but it can be a useful product for quality controlling issues with the radar. If you know one thing about differential phase, it should be that when calibrated properly phi values should be around 60 degrees when entering the first precipitation returns on the radial. This value is known as Initial System Differential Phase, or ISDP. In this example, the ISDP is a little higher than that and is closer to 90 degrees. If ISDP is a little high, that’s not a big problem. If ISDP is low, like near 0 degrees, then you can run into issues. This example has a few radials where ISDP is low due to some interference. It may be a little hard to see, but some of the values are pink, meaning the values have wrapped around to the high 300s. Since this is interference, we know the data is bad. If it happens in areas you know is precip, your CC and other dual-pol data can be negatively impacted."> <Style FontSize="12" /> </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="Our discussions up to this point identified a variety of base data quality issues, what may cause them, and possibly even some mitigation steps. Here are some additional mitigation steps you can take to help get the best quality data possible. Click on the five buttons."> <Style FontSize="12" /> </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="Antenna rotation rates can impact data quality. The best way to mitigate data quality issues due to radar rotation rates is to use the available VCPs in the situations they were designed for. For example, VCP 215 is a great choice for many types of precipitation events as it was designed for general surveillance. If severe convection is a threat, switch to VCP 212. Just remember to switch back to VCP 215 if severe convection ceases to be a threat during the event."> <Style FontSize="12" /> </Span> <Span Text="
" /> </Block> <Block> <Style /> </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="The CMD algorithm is your best option for identifying clutter and getting the highest quality radar base data. If you notice false positive detections where data is dropping out where it should not, make sure you are using the best VCP for the current weather situation. If you notice false negative detections where clutter isn’t being removed, then you have two options. First, you can create a sector where all bins clutter filter occurs. You will want to make sure this sector is as small as possible because filtering every bin will definitely impact your base data. If that doesn’t work, probably because the returns have a non-zero velocity, then you will need to use an exclusion zone. Exclusion zones are your tool of last resort, so you definitely want to use them judiciously."> <Style FontSize="12" /> </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="While differential attenuation and non-uniform beam filling often occur in similar conditions, their physical causes are different. Differential attenuation impacts the differential reflectivity product while non-uniform beam filling will impact the correlation coefficient product. In the example shown, see how the radial spikes don’t always match up between ZDR and CC. If you notice either artifact in your base data, then it’s likely that your hydroclassification and dual-pol precipitation products will be negatively impacted, too. You will need to make adjustments for QPE rainfall totals for these areas if the conditions linger over the same locations for more than a volume scan or two."> <Style FontSize="12" /> </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="Differential phase can be a very useful tool for diagnosing data quality issues. Look at PhiDP values in areas you know precipitation is close to the radar to ensure that your initial system differential phase values are around 60 degrees, especially if your radar has had maintenance recently. Also, check those ISDP values if you suspect widespread attenuation in Z or ZDR. Just don’t get hung up on the noisy PhiDP values in clear air or clutter returns. Those will not tell you much. You need returns from actual precipitation to know if your radar has a problem."> <Style FontSize="12" /> </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="The Data Quality Dashboard, found on the MSCF, can be another useful mitigation tool. This tool allows radar operators to identify whether the current differential reflectivity calibration is within accepted tolerance limits. The dashboard shows not only the overall bias, but also the bias value for the rain, snow, and Bragg bias calculation methods. Likewise, you can also get an estimate of the rain rate error for the R(Z, ZDR) accumulation for different reflectivity values based on the current calibration bias. Click on this gauge to see how the bias values change color when they exceed the tolerance limits. Then click on the shade charts button to see how these values change over time. Finally, click on the shift change checklist button to see another place where you can find the ZDR bias.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Shade Charts"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": The shade charts show how the ZDR bias values change over time for all three calculation methods. The color scheme on these charts is a little different than on the main dashboard. Here, any positive bias value will appear red while negative bias values appear blue. You then use the two dashed lines in each graph to determine if the values are within the tolerance limits of +/- 0.2 dB. If the calibration is routinely outside of these limits, you should tell your radar focal point and/or El tech. They can then reach out to the ROC Hotline for further assistance on the issue.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Shift Change Checklist"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": Besides using the Data Quality Dashboard to identify ZDR bias, you can also find this information on the Shift Change Checklist. The ZDR bias listed in this product will be an average from the previous day. So, if for some reason your radar goes down, the bias estimate listed here will say unknown until the day after you get sufficient data to make an estimate.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="
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"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text=""> <Style FontSize="12" /> </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="Click on the four buttons to learn about other data quality resources available to NWS forecasters.
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"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="WDTD"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": For starters, feel free to contact the Warning Decision Training Division staff with any radar related questions you have. Even when we don’t know the answer, we can usually connect you with someone who does.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="ROC Hotline"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": If you notice something unusual or problematic going on with your WSR-88D, you will definitely want to give the Radar Operations Center Hotline staff a call. Just remember that the ROC Hotline is only available to National Weather Service, Air Force, and Federal Aviation Administration personnel since they are the tri-agency radar operators.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="WSR-88D Email Forum"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": There is an email forum for the WSR-88D. All you need to do is subscribe to that forum on VLab, and you will be included in the conversation.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Shift Change Checklist"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": The RPG routinely generates the Shift Change Checklist product with lots of important information about how the WSR-88D system is operating. What’s nice about this product is you can pull it up on AWIPS. So, that radar checklist that you are supposed to do once a shift? Well, now you can do it from AWIPS instead of going over to the MSCF. Click this button to see an example.
"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text="Example"> <Style FontSize="12" FontIsItalic="True" /> </Span> <Span Text=": In this example we have a mismatch going on between the PPS and QPE algorithms. The PPS algorithm is using a convective Z-R relationship. However, the dual-pol QPE algorithm has been switched over to a tropical R(Z,ZDR) relationship. This kind of mismatch can lead to problems when comparing the output of the two algorithms.
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"> <Style FontSize="12" /> </Span> </Block> <Block> <Style /> <Span Text=""> <Style FontSize="12" /> </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="Time to summarize this lesson. This lesson covered some common data artifacts seen in base reflectivity, base velocity, and dual-pol products, several general mitigation steps forecasters can take to get the best data quality possible, and additional data quality resources at your disposal. The next slide will start the quiz. Click the “next” button when you are ready to proceed."> <Style FontSize="12" /> </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="If you have any questions, comments, or would like more information about the subject matter presented in this lesson please feel free to contact us at the email addresses listed here. I would also like to thank Andy Wood for providing the content for this lesson. You are now finished with this module."> <Style FontSize="12" /> </Span> </Block> </Content> </Document>