active Closed captions. Press the spacebar to toggle captions on and off. definition finish locked next pause play previous replay resources search Skip navigation. Press enter to return to the slide. slide progress submit submit all %count% of %total% item visited %count% of %total% items visited step %count% of %total% visited volume Accessible text Toggle accessible text Action Alt Bio Check to include Clear and return to menu Close Captions Toggle captions Toggle closed captions Continue Continue Ctrl Definition Start Course Please rotate your device Enable keyboard shortcuts Enter Exit Filter FINISH Glossary Keyboard Shortcuts Keyboard shortcuts Start Course More info Mute / unmute Mute NEXT Next slide Next slide Menu Pause Play Play / pause PREV Previous slide Previous slide hour hours minute minutes second seconds Question List Replay slide Replay Resources Restart Resume Search... Search in: Search Results Search Send an email Settings Shift Shortcut List keyboard shortcuts Sidebar Toggle Slide Text Space SUBMIT Submit slide Submit SUBMIT ALL Terms audio camera moved down camera moved left camera moved right camera moved up %count% of %total% %count% of %total% visited hotspot Use the w, a, s, and d keys to move around the 360 degree image. Press the tab key to jump to interactive markers and hotspots. 360 degree image interaction free exploration mode guided tour mode next previous step item items label marker of pause audio pause video play audio play video progress progress %total% item %total% items video video volume visited Toggle zoom to fit Notes Notes Unmute Zoom to fit <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="Welcome to Principles of Radar! My name is Katy Christian and I’ll be your guide through today’s lesson over the Legacy Precipitation Processing Subsystem algorithm, referred to as the Legacy PPS." /> </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, go ahead and click “Next” to continue." /> </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="Just for some context, here is the roadmap for the entire Radar Principles section of RAC - right now, you are here so let’s keep moving forward! "> <Style FontFamily="+minor" FontSize="9" ForegroundColor="#444444" 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="The learning objectives for this lesson are short and sweet: to understand what the Legacy PPS algorithm is and how it works. Let’s get started!" /> </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="So what is the Legacy PPS? It is essentially a process that uses multiple algorithms and quality control checks to estimate the areal rainfall from radar data. As a broad overview, the Legacy PPS can be broken up into three steps. It first first obtains the necessary radar data from the RDA. It will then quality control this data. Lastly, it will generate multiple different rainfall products for your use. Now I know it might be nice if we could just stop there but we need to go into more detail as there are several adaptable parameters that you as a forecaster need to know about if you’re to use and understand this rainfall algorithm. So, without further ado, let’s dive into more details about how it works!" /> </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="Okay, from the looks of this slide, I bet you’re thinking, “Wait a minute, I thought this was supposed to be a lesson over the Legacy rainfall algorithm?” You are correct but who says we can’t have a little fun while we’re at it! So here is the game plan for today’s lesson. Your goal as the learner, or PacMan in this case, is to make it through the maze without being caught by common enemies of RAC distance learning - these include “fatigue”, “distractions”, “boredom”, or the ultimate nemesis, “no caffeine.” When you arrive at each sign post, click on it to learn more and when you are done, you’ll be quickly tested so see if you’ve retained the material. Beware that if you do not succeed, you may overrun by the enemies shown within the maze. So, good luck to you and to get started, click on PacMan to begin your journey! " /> </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="The first step in the Legacy PPS Algorithm is to obtain reflectivity, velocity, and spectrum width from the Radar Data Acquisition Unit, or RDA. The Legacy PPS will then use this base data as input for several different algorithms and quality checks that we will discuss shortly. 
" /> </Block> <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="The Radar Echo Classification algorithm is a essentially a fuzzy logic algorithm that quality controls the data. It works by using Z, V, and SW values to assign a percentage likelihood that a particular bin contains clutter. This percentage value will also be used later on as we will see. 
" /> </Block> <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="EPRE, or the Enhanced Precipitation Preprocessing algorithm, essentially prepares the data for rainfall product generation. This algorithm is composed of several steps so we will work them one by one. To start, EPRE begins with a parameter called CLUTTHRESH. CLUTTHRESH looks at the clutter likelihood percentage that was designated by REC, or Radar Echo Classifier, earlier. If REC designates a bin as having less than or equal to 50% clutter, CLUTTHRESH allows the dBZ associated with this bin to be converted to rainfall. If a bin is designated as having > 50% clutter, CLUTTRESH rejects this bin for conversion to rainfall and it will then check the next highest tilt to see if this condition is met.
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" /> </Block> <Block> <Span Text="One thing for you to know is that CLUTTHRESH is editable at the RPG! Although the default value is set to 50%, you can change this. Here’s an example where CLUTTHRESH was increased to 75% in an area of very little terrain clutter. Before changing any parameters, just be sure to always talk it over with your radar focal point or the lead forecaster on duty. Once this condition is met, EPRE will then determine the start and end period over which to accumulate rainfall. Click on the highlighted box to continue the flowchart! " /> </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="To determine the rainfall accumulation period, two conditions must be met. First, a parameter called RAINZ represents the minimum dBZ that must be met in order for EPRE to start accumulating rainfall. As a default, RAINZ must exceed 20 dBZ in order for bins to count as precipitation returns. Next, RAINA represents the areal coverage of RAINZ that must be met in order for EPRE to start accumulating rainfall. By default, RAINA must exceed 80 km^2. To the left is an example where both these conditions are satisfied. It’s important for you to know that both RAINZ and RAINA are editable at the RPG and the below figure shows an example of this where RAINA was increased to 100 km^2. This is often done if the minimum area set by RAINA is too small and is accumulating clutter instead of precipitation. Once precipitation returns of at or > 20 dBZ are detected over 80 km^2, the Legacy PPS begins accumulating rainfall and will continue to do so as long as thresholds are satisfied. If conditions are not met for one hour, rainfall accumulations will reset. You can also manually reset rainfall accumulations in the RPG Control window.
" /> </Block> <Block> <Span Text="
" /> </Block> <Block> <Span Text="I quickly want to mention that within EPRE, there is a quality control caveat referred to as “Exclusion Zones” that prevents reflectivity from residual clutter from terrain or moving sources of clutter from being converted to rainfall. You will want to make use of this quality control option if you have a chronic clutter problem. Exclusion Zones can be defined at the RPG. 
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" /> </Block> <Block> <Span Text="The final step of the EPRE algorithm is to build both the Hybrid Scan Reflectivity and the Digital Hybrid Scan Reflectivity products. In order to do this, dBZ bins must meet the following conditions: 1) CLUTTHRESH < 50%, 2) must not fall within an exclusion zone, and 3) beam blockage must be < 50%. Once these 3 conditions are met, the EPRE algorithm is done!" /> </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="The Rain Rate algorithm works by taking the dBZ values from the earlier step and converting them to rain rate using whatever Z-R relationship is set at the RPG. The rain rate algorithm also applies a parameter called Max Precipitation Rate that caps high rain rates that are a result of hail contamination. The default rain rate cap is 103.8 mm/hr, or 4.09 in/hr as shown in the below image. If you are using the tropical Z-R relationship, it is recommended that you increase the hail cap to 154.2 mm/hr, or 6.00 in/hr. Speaking of Z-R relationships, it can often be confusing to know which Z-R relationship to choose leading up to a given event. With that in mind, click on the following icon to learn more. Once you’re done, you’ll be redirected to the next slide." /> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Style FlowDirection="LeftToRight" LeadingMargin="0" TrailingMargin="0" FirstLineMargin="0" Justification="Left" CustomTabStops="" LineSpacingRule="Multiple" LineSpacing="23" SpacingBefore="0" SpacingAfter="10"> <ListStyle ListType="None" ListTypeFormat="Parentheses" Color="#000000" BulletFont="Arial" /> </Style> <Span Text="The rain accumulation algorithm takes the rain rates previously calculated and accumulates them over different durations. There are two different durations over which it accumulates. The first is a continuous accumulation where as long as RAINZ and RAINA are satisfied, it will continue to accumulate rainfall. An example of a continuous accumulation is the Storm Total Precipitation, or STP, as shown on the right. The accumulation start time for this product can be found in the upper left hand corner. 
"> <Style FontFamily="+minor" FontSize="9" FontIsBold="False" FontIsItalic="False" FontIsUnderline="False" FontIsStrikeout="False" /> </Span> </Block> <Block> <Style FlowDirection="LeftToRight" LeadingMargin="0" TrailingMargin="0" FirstLineMargin="0" Justification="Left" CustomTabStops="" LineSpacingRule="Multiple" LineSpacing="23" SpacingBefore="0" SpacingAfter="10"> <ListStyle ListType="None" ListTypeFormat="Parentheses" BulletFont="Arial" /> </Style> <Span Text="The next type of accumulation is hourly accumulations where the hourly end time is either the current volume scan or the top of each hour. Some examples of hourly accumulations include the one-hour precipitation as shown in the figure to the right, three hour precipitation, or user selectable precipitation. "> <Style FontFamily="+minor" FontSize="9" FontIsBold="False" FontIsItalic="False" FontIsUnderline="False" FontIsStrikeout="False" /> </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 FlowDirection="LeftToRight" LeadingMargin="0" TrailingMargin="0" FirstLineMargin="0" Justification="Left" CustomTabStops="" LineSpacingRule="Multiple" LineSpacing="23" SpacingBefore="0" SpacingAfter="0.5"> <ListStyle ListType="None" ListTypeFormat="Parentheses" BulletFont="Arial" /> </Style> <Span Text="The adjustment bias algorithm is optional and gives users the ability to apply a bias multiplier to the rainfall accumulations. In AWIPS, the Multi-Sensor Precipitation Estimator (MPE) compares radar rainfall estimates to gauge data and sends a bias table to the RPG every hour. A parameter known as the Bias Flag controls the ability to apply the bias and by default, it is set to false. Setting the Bias flag to true will apply the bias generated by the MPE out to a range of 124 nm. However, a word of caution: the MPE bias output is NOT perfect due to some of the issues shown on the slide. With those in mind, it is recommended that you do not mess with changing the default bias flag as doing so can potentially create more issues. If you’re interested in learning more about biases, please take the WDTD lesson titled “Interpreting QPE Bias Information in AWIPS.” "> <Style FontFamily="+minor" FontSize="9" FontIsBold="False" FontIsItalic="False" FontIsUnderline="False" FontIsStrikeout="False" /> </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="Congratulations on passing the quiz and completing this module! You have lived to see another module, of which you can see on this image here what comes next. Once you’re finished, click the “Exit” button to close this lesson. "> <Style FontFamily="+minor" FontSize="9" ForegroundColor="#444444" LinkColor="#444444" /> </Span> </Block> </Content> </Document>