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Slide Text Space SUBMIT ALL submit all SUBMIT submit Submit Unmute volume radar beam characteristics principles of meteorological doppler radar warning decision training division technical problems? if you encounter any technical problems with this lesson, please contact the rac team directly by e-mail (nws.wdtd.rachelp@noaa.gov) or you can use the wdtd feedback forum web page (https://training.weather.gov/wdtd/contact/feedback.php) to send us a message. 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 review lesson take your time and review the lesson content provided in this presentation. review lesson course completion information 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 review lesson complete the quiz technical problems? roadmap learning objectives identify why the wsr-88d emits discrete pulses identify how the beam width is determined for radar beams identify how a radar beam’s physical size relates to range from radar identify how power density relates to transmitted power and range from radar identify why rayleigh scattering is important to wsr-88d interpretation identify the various product resolutions and precisions for wsr-88d products radar beam characteristics discrete pulses beam width physical size power density backscatter power spatial resolution product resolution discrete pulses pulse #3 pulse #2 pulse #1 allows for range determination of intercepted targets physical size the beam increases in size continually down range range = 10 km width = 990 ft range = 120 km width = 11,830 ft range = 230 km width = 22,680 ft beamwidth length of portion of beam where power is one-half peak transmitted power beam width peak power half power half power wsr-88d approximately 1° smeared by antenna rotation power density the amount of power intercepting the targets directly related to transmitter power inverse relation to beam size (range) close range high power density mid-range lower power density long-range low power density backscattered power amount of power returned to radar after target intercepts transmitted power size rayleigh scattering vs mie scattering shape simple scattering complex scattering state dielectric constant liquid reflects more power than ice concentration higher concentration results in higher power return rayleigh scattering occurs when intercepting target is small compared to wavelength of radar beam results in linear relationship between power return and target size wsr-88d (10-11 cm wavelength) valid for rain drops (< 7 mm) mie scattering results in oscillating relationship between power return and target size wsr-88d valid for hail occurs when intercepting target is similar in size compared to wavelength of radar beam spatial resolutions the amount of detail resolved by the radar - determined by pulse duration and angular beam width angular resolution = 1° super-resolution uses 0.5° using processing techniques angular resolution range resolution = 250 m lower resolutions of 500 m, 1 km, 2 km, and 4 km available by averaging range resolution product resolution how close the displayed value is to the true value true values are binned to conserve bandwidth higher # bins = more bandwidth more bins = more precise 5 10 5, 6, 7, 8, 9 or 10 5 7 5, 6, or 7 summary the 88d emits discrete pulses to determine the range of intercepted targets. beam width is determined at the point at which the power along the beam reaches one-half the peak transmitted power (appx. 1 degree). a beam's physical size increases continually down range from the radar. power density is directly related to transmitter power and inversely related to beam size. rayleigh scattering occurs for rain drops with the 88d, resulting in a linear relationship between power return and target size. product resolution determines how close the displayed value is to the true value. incorrect incorrect. color is not decipherable with weather radars. continue continue continue continue continue continue incorrect incorrect. shape is possible to infer by comparing the returned power intensities from the horizontal and vertical polarizations. continue continue continue continue continue continue incorrect incorrect. the intensity is measured by the power returned from the weather echo. continue continue continue continue continue continue incorrect correct! continue continue continue continue continue continue ques. #1 of 7: the wsr-88d transmits discrete pulses of energy in order to determine ________ of the echoes detected. range range range range range range intensity intensity intensity intensity intensity intensity shape shape shape shape shape shape color color color color color color incorrect incorrect. power cannot increase after it has been transmitted. continue continue continue continue continue continue incorrect incorrect. power cannot increase after it has been transmitted. continue continue continue continue continue continue incorrect incorrect. it is a point where the power decreases, but it’s a little more than 1/3. continue continue continue continue continue continue incorrect correct! continue continue continue continue continue continue ques. #2 of 7: beam width is determined by the point where the peak transmitted power ______ by ______. decreases; one-half decreases; one-half decreases; one-half decreases; one-half decreases; one-half decreases; one-half decreases; one-third decreases; one-third decreases; one-third decreases; one-third decreases; one-third decreases; one-third increases; one-half increases; one-half increases; one-half increases; one-half increases; one-half increases; one-half increases; one-fourth increases; one-fourth increases; one-fourth increases; one-fourth increases; one-fourth increases; one-fourth incorrect incorrect. remember the beam spreads out as it propagates down radial. continue continue continue continue continue continue correct correct! continue continue continue continue continue continue ques. #3 of 7: a beam’s physical size increases continually as the pulse propagates down radial. true true true true true true false false false false false false incorrect incorrect. antenna size doesn’t play a significant role in power density. continue continue continue continue continue continue incorrect incorrect. antenna height does not play a role in power density. continue continue continue continue continue continue incorrect incorrect. wavelength and antenna size don’t play a significant role in power density. continue continue continue continue continue continue incorrect correct! continue continue continue continue continue continue ques. #4 of 7: power density is directly related to _______ and inversely related to ________. peak transmitted power; beam size (range) peak transmitted power; beam size (range) peak transmitted power; beam size (range) peak transmitted power; beam size (range) peak transmitted power; beam size (range) peak transmitted power; beam size (range) wavelength; antenna size wavelength; antenna size wavelength; antenna size wavelength; antenna size wavelength; antenna size wavelength; antenna size antenna height; peak transmitted power antenna height; peak transmitted power antenna height; peak transmitted power antenna height; peak transmitted power antenna height; peak transmitted power antenna height; peak transmitted power peak transmitted power; antenna size peak transmitted power; antenna size peak transmitted power; antenna size peak transmitted power; antenna size peak transmitted power; antenna size peak transmitted power; antenna size incorrect incorrect. this answer is completely made up! continue continue continue continue continue continue incorrect incorrect. only rain is similar in shape, and that even changes. ice crystals and hail can take on many different shapes. continue continue continue continue continue continue incorrect incorrect. this describes mie scattering continue continue continue continue continue continue incorrect correct! continue continue continue continue continue continue ques. #5 of 7: which statement best describes why the rayleigh approximation is mostly valid for wsr-88d interpretation? the majority of weather targets are small compared to the wavelength of the wsr-88d the majority of weather targets are small compared to the wavelength of the wsr-88d the majority of weather targets are small compared to the wavelength of the wsr-88d the majority of weather targets are small compared to the wavelength of the wsr-88d the majority of weather targets are small compared to the wavelength of the wsr-88d the majority of weather targets are small compared to the wavelength of the wsr-88d the majority of weather targets are similar in size compared to the wavelength of the wsr-88d the majority of weather targets are similar in size compared to the wavelength of the wsr-88d the majority of weather targets are similar in size compared to the wavelength of the wsr-88d the majority of weather targets are similar in size compared to the wavelength of the wsr-88d the majority of weather targets are similar in size compared to the wavelength of the wsr-88d the majority of weather targets are similar in size compared to the wavelength of the wsr-88d all weather targets are similar in shape resulting in a linear relationship between power return and size all weather targets are similar in shape resulting in a linear relationship between power return and size all weather targets are similar in shape resulting in a linear relationship between power return and size all weather targets are similar in shape resulting in a linear relationship between power return and size all weather targets are similar in shape resulting in a linear relationship between power return and size all weather targets are similar in shape resulting in a linear relationship between power return and size rayleigh discovered radar could be used for weather detection while studying bugs rayleigh discovered radar could be used for weather detection while studying bugs rayleigh discovered radar could be used for weather detection while studying bugs rayleigh discovered radar could be used for weather detection while studying bugs rayleigh discovered radar could be used for weather detection while studying bugs rayleigh discovered radar could be used for weather detection while studying bugs incorrect incorrect. the higher the number of bits, the more data levels. continue continue continue continue continue continue correct correct! continue continue continue continue continue continue ques. #6 of 7: match the following data level descriptions with the corresponding number of data levels. 3-bit 8 levels 4-bit 16 levels 8-bit 256 levels incorrect incorrect. too coarse of resolution for both continue continue continue continue continue continue incorrect incorrect. too coarse of resolution for both continue continue continue continue continue continue incorrect incorrect. almost true though… remember that with data processing techniques, the azimuthal resolution can be brought down from 1 deg to 0.5 deg. continue continue continue continue continue continue incorrect correct! continue continue continue continue continue continue ques. #7 of 7: identify the best possible range and azimuthal resolution for base reflectivity and velocity. 250 meters; 0.5 deg 250 meters; 0.5 deg 250 meters; 0.5 deg 250 meters; 0.5 deg 250 meters; 0.5 deg 250 meters; 0.5 deg 250 meters; 1 deg 250 meters; 1 deg 250 meters; 1 deg 250 meters; 1 deg 250 meters; 1 deg 250 meters; 1 deg 1 km; 10 deg 1 km; 10 deg 1 km; 10 deg 1 km; 10 deg 1 km; 10 deg 1 km; 10 deg 10 km; 5 deg 10 km; 5 deg 10 km; 5 deg 10 km; 5 deg 10 km; 5 deg 10 km; 5 deg completion! <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 WSR-88D Radar Beam Characteristics. This is presented by the Warning Decision Training Division (WDTD). Let’s get started!"> <Style FontFamily="+major" FontSize="10.5" 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> <Span Text="If you are completing this course for credit, please review this interaction on how to complete this course within the NWS Learning Center. After viewing all the slides, click “Next” to continue."> <Style FontSize="10.5" /> </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” section of RAC. You are currently in the WSR-88D Fundamentals portion of this section. Let’s keep going!"> <Style FontFamily="Open Sans" FontSize="10.5" 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 /> <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="10.5" /> </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 radar beam has many different characteristics which help determine the information you will see as a warning forecaster. These various characteristics include: discrete pulses, beam width, physical size, power density, backscatter power, spatial resolution, and product resolution. Click on each of these characteristics to learn more. Once you have completed viewing each of these characteristics, you will be ready for the quiz to test your understanding."> <Style FontSize="10.5" /> </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 WSR-88D emits pulses of energy into the atmosphere at pre-defined intervals. This discrete pulse mode allows for the radar signal processor to determine the range of the intercepted targets. "> <Style FontSize="10.5" /> </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 the beam width does not change down range from the radar, the physical size does increase quite dramatically down range. Let’s quickly look at how big the WSR-88D pulse gets as we approach the far reaches of the WSR-88D range. At 10 km from the radar, the width of the beam is already 990 feet. That’s almost 3 football fields! When the beam gets to the 120 km range, the width is over 2 miles! And, when the beam gets to the outer edges of the first trip (which we’ll define later), the beam is over 4 miles. So, targets within one radar beam can be as far as 4 miles apart."> <Style FontSize="10.5" /> </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 radar generates the electromagnetic radiation at the transmitter and the antenna focuses this radiation into a beam that is then reflected into the atmosphere toward the intended targets. Since the radiation doesn’t have boundaries, the beamwidth is determined at the point where the power along the beam reaches one-half of the beam's peak transmitted power. This distance is generally measured in degrees and is approximately 1 degree for the WSR-88D. This can be somewhat broader due to the rotation of the antenna while the beam is being transmitted, which is referred to as the effective beam width. "> <Style FontSize="10.5" /> </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 purpose of sending out a pulse of radiation is to have weather targets intercept this energy and reflect some of it back to the radar. This way, we can determine the intensity of the weather targets. The amount of energy that intercepts these weather targets is called the power density, and it is dependent upon two factors: transmitter power and beam size. First, power density will increase with increasing transmitter power. However, as the beam goes down range, remember it increases in size, so that same amount of power is spread across a larger area and the power density actually decreases as the beam goes down range. The power density is not equally distributed across the beam. The beam centerline actually contains most of that power. "> <Style FontSize="10.5" /> </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=" Once the target intercepts some of the transmitted power, it reflects some of the power back to the radar. The amount of power returned back to the radar is referred to as “backscattered power” and it is dependent upon 4 characteristics of the weather target. One is size (which we’ll discuss shortly). The next is shape. Fairly smooth-shaped objects like rain drops will have simple scattering properties, but spiky hail stones will have complex scattering properties. The next is the state of the weather target. We’ll also refer to this as the dielectric constant which basically means “how reflective is the weather target”. Liquid reflects radar energy much more effectively than ice. Therefore, for the same exact size/shape, water will return a significantly higher amount of power than an ice particle. Finally, we have concentration. Within a given beam, if there only a few rain drops, for example, the power returned will be fairly low. However, if you take those same rain drops and increase the amount by triple… the amount of power returned will increase. So, these are the four factors affecting backscattered power, but let’s dive a little deeper into the relationship between size and power return. "> <Style FontSize="10.5" /> </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 size of the weather target compared to the wavelength of the radar determines the scattering regime. For targets that are small compared to the wavelength of the radar beam, the scattering is fairly uniform in all directions and the amount of power reflected increases linearly with increasing size. This type of scattering is called Rayleigh scattering and it is preferred because the linear relationship between power return and target size is very helpful (as we’ll find out later). The wavelength of the WSR-88D is approximately 10 cm. Therefore, Rayleigh scattering is a good assumption for all weather targets smaller than 7 mm which includes practically all rain, but does not include hail. This basically means for most weather objects, the power returned is linearly related to the size of the weather target. "> <Style FontSize="10.5" /> </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=" When weather targets become roughly similar in size to the wavelength of the radar beam or larger, the scattering properties are no longer linearly related, and most of the energy is forward scattered. The energy that is reflected back to the radar does not have a linear relationship to size, but rather an oscillating relationship. This is called Mie scattering. So, relating size to power return is not so straightforward. For the WSR-88D, hail is the primary target that falls within the Mie scattering regime."> <Style FontSize="10.5" /> </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, how much detail can we see with data collected by the WSR-88D? That is all dependent upon the pulse duration and angular beam width. Since we already know the beam width is 1 degree, that is the best angular resolution we can get without any processing of the data. I say “without any processing” because radar engineers came up with a processing technique to display 0.5 degree angular resolution data, which is called “super-resolution”. This technique will be covered in a later lesson in this section, but for now, just know it "> <Style FontSize="10.5" /> </Span> <Span Text="is"> <Style FontSize="10.5" FontIsItalic="True" /> </Span> <Span Text=" possible to get 0.5 degree angular resolution with the WSR-88D. As for the range resolution, this is determined by the pulse duration (or how long does the pulse transmit). The longer the pulse duration, the coarser the range resolution. For the WSR-88D, the best range resolution possible is 250 m. Other coarser resolutions are available by averaging the individual 250-m bins. "> <Style FontSize="10.5" /> </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=" Once the information is received at the radar, it has to be quantified and binned to be displayed. The more bins you have to fit the data into, the more precise the value displayed is to the real value. For example, if you have a bin that contains values from 5 to 10, then any real value from 5 to 10 will be displayed as 5. However, if you have a bin that contains only values from 5 to 7, then only values from 5 to 7 will be displayed as 5. In other words, the second example has higher precision. The reason for binning the data is to conserve bandwidth. For the WSR-88D, there are three basic binning levels… these are 3-bit, 4-bit, and 8-bit. 3-bit has 8 data levels, 4-bit has 16 data levels, and 8-bit has 256 data levels. So, 8-bit data is more precise than the 3-bit or 4-bit counterparts, but it takes up more bandwidth. More of this will be discussed in the base and derived products section of RAC, but for now, just know the three different levels of binning. "> <Style FontSize="10.5" /> </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=" Let’s quickly review what we’ve learned in this lesson. The 88D emits discrete pulses to determine the range of intercepted targets. Beam width is determined at the point at which the power along the beam reaches one-half the peak transmitted power (appx. 1 degree). A beam's physical size increases continually down range from the radar. Power density is directly related to transmitter power and inversely related to beam size. Rayleigh scattering occurs for rain drops with the WSR-88D, resulting in a linear relationship between power return and target size. And finally, product resolution determines how close the displayed value is to the true value. Click next when you’re ready to take the quiz. "> <Style FontSize="10.5" /> </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=" Thanks for your attention! You have now completed this lesson. "> <Style FontSize="10.5" /> </Span> </Block> </Content> </Document>