Topic 3: Principles of Meteorological Doppler Radar

[Pages:39]Distance Learning Operations Course

Topic 3: Principles of Meteorological Doppler Radar

Presented by the Warning Decision Training Branch

Version: 0609

Distance Learning Operations Course

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Topic 3: Principles of Meteorological Doppler Radar

Distance Learning Operations Course

Topic 3: Principles of Meteorological Doppler Radar

Table of Contents

Topic 3, Lesson 1: WSR-88D Fundamentals ........................................... 3 - 7

WSR-88D Fundamentals (self guided web module) ...........................................3 - 8 Objectives...............................................................................................................3 - 8

Topic 3, Lesson 2: Signal Processing.................................................... 3 - 11

Signal Processing (instructor guided web module).........................................3 - 12 Objectives............................................................................................................. 3 - 12 Radial Velocity (Objective 1)............................................................................... 3 - 12

Key Points About Radial Velocity ...................................................................................... 3 - 13 Radial Speed Equation ...................................................................................................... 3 - 13 Examples........................................................................................................................... 3 - 16 .......................................................................................................................................... 3 - 17

The Doppler Effect (Objective 2) ........................................................................ 3 - 17

Sound Wave Example ....................................................................................................... 3 - 20 WSR-88D Pulse Example ................................................................................................. 3 - 21 WSR-88D Velocity Detection Method................................................................................ 3 - 21 Phasors ............................................................................................................................. 3 - 22 Phasors for Two Pulses..................................................................................................... 3 - 23

WSR-88D Radial Speed Computation (Objective 3) .........................................3 - 24

Maximum Unambiguous Velocity ..................................................................................... 3 - 25 Phase Shift-Radial Speed Relationship............................................................................. 3 - 26 Phase Shift Depiction Using Phasors................................................................................ 3 - 26 Phase Shift and Unambiguous Velocity............................................................................. 3 - 27

Obtaining I and Q Values (Objective 4)............................................................. 3 - 30

I and Q Components ......................................................................................................... 3 - 30 Both I and Q Values Needed ............................................................................................. 3 - 31 Determining Target Direction ............................................................................................. 3 - 31 Calculations Using Phasors .............................................................................................. 3 - 34 Actual Phase Shift Exceeds 180? ................................................................................................3 - 35 Calculations Using Phasors .............................................................................................. 3 - 35 Key Points ......................................................................................................................... 3 - 37 Signal Processing Review Exercises ................................................................................ 3 - 38

Topic 3, Lesson 3: Base Data Generation.............................................. 3 - 41

Base Data Generation (instructor guided web module)................................... 3 - 42 Objectives............................................................................................................. 3 - 42 Base Data Estimation Considerations (Objective 1) ........................................ 3 - 42

Base Reflectivity Data ....................................................................................................... 3 - 42 Base Mean Radial Velocity Data ....................................................................................... 3 - 43 Base Spectrum Width Data ............................................................................................... 3 - 45

Spectrum Width - Meteorological Factors (Objective 2) ................................. 3 - 47

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Distance Learning Operations Course

Spectrum Width - Nonmeteorological Factors (Objective 3) .......................... 3 - 49

Base Data Generation Review Exercises.......................................................................... 3 - 50

Topic 3, Lesson 4: Clutter Suppression................................................. 3 - 53

Clutter Suppression (instructor guided web module)...................................... 3 - 54

A Note on Terminology ...................................................................................................... 3 - 54

Objectives............................................................................................................. 3 - 54 Clutter Contamination on Base Products (Objective 1) ................................... 3 - 54

Ground Clutter Contamination General Characteristics .................................................... 3 - 55 Reflectivity Products .......................................................................................................... 3 - 55 Mean Radial Velocity Products.......................................................................................... 3 - 56 Spectrum Width Products .................................................................................................. 3 - 57

Anomalous Propagation (AP) on Base Products (Objective 1)....................... 3 - 58

AP Clutter General Characteristics ................................................................................... 3 - 58 Reflectivity Products .......................................................................................................... 3 - 59 Mean Radial Velocity Products.......................................................................................... 3 - 60 Spectrum Width Products .................................................................................................. 3 - 60

Clutter Suppression Technique: GMAP............................................................. 3 - 61

Reference .......................................................................................................................... 3 - 61 Clutter vs. Meteorological Signal ....................................................................................... 3 - 62 GMAP Performance Examples ......................................................................................... 3 - 63

Application of Ground Clutter Suppression .................................................... 3 - 69

Filtering of Normal vs. Transient Clutter ............................................................................ 3 - 69 Clutter Filter Bypass Map(s) .............................................................................................. 3 - 69 Bypass Map Generation Process ...................................................................................... 3 - 70 Clutter Suppression Regions Files .................................................................................... 3 - 73 Clutter Regions Window .................................................................................................... 3 - 74 Clutter Regions Window .................................................................................................... 3 - 76 Editing/Creating Clutter Regions ....................................................................................... 3 - 78 Clutter Filter Control (CFC) Product .................................................................................. 3 - 80 Examples of Data With and Without Proper Clutter Filtering............................................. 3 - 83 Negative Effects When All Bins Inappropriately Applied ................................................... 3 - 86 Ground Clutter Suppression Limitations (Objective 3) ...................................................... 3 - 92 Appropriate Ground Clutter Suppression Strengths (Objective 3)..................................... 3 - 93 Clutter Suppression Review Exercises.............................................................................. 3 - 94

Topic 3, Lesson 5: Mitigation of Data Ambiguities ............................... 3 - 97

Mitigation of Data Ambiguities (teletraining) .................................................... 3 - 98 Objectives............................................................................................................. 3 - 98 PRF effects on Rmax and Vmax (Objective 1) ..................................................... 3 - 99

Rmax Definition .................................................................................................................. 3 - 99 Vmax Definition................................................................................................................... 3 - 99 Key Points ......................................................................................................................... 3 - 99 "Doppler Dilemma" .......................................................................................................... 3 - 100

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Topic 3: Principles of Meteorological Doppler Radar

Data Recognition and Algorithms (Objectives 2 & 3)..................................... 3 - 101 Range Folding.................................................................................................... 3 - 101

Often on Velocity and Spectrum Width Products............................................................. 3 - 102 Rarely on Reflectivity Products........................................................................................ 3 - 102

Range Unfolding Algorithm .............................................................................. 3 - 104

Non-overlaid Echoes Case.............................................................................................. 3 - 105 Overlaid Echoes Case......................................................................................................3 - 110 The Effects of TOVER ......................................................................................................3 - 113 Range Unfolding Algorithm ..............................................................................................3 - 114 Strengths ..........................................................................................................................3 - 114 Limitations ........................................................................................................................3 - 114

Improperly Dealiased Velocities....................................................................... 3 - 115 Velocity Dealiasing Algorithm .......................................................................... 3 - 119

Step 1: Radial Continuity Check ...................................................................................... 3 - 120 Step 2: Nine Point Average ............................................................................................. 3 - 121 Step 3: Expanded Search................................................................................................ 3 - 122 Step 4: Environmental Winds .......................................................................................... 3 - 122 Error Checks ................................................................................................................... 3 - 124 Velocity Dealiasing Algorithm .......................................................................................... 3 - 124 Strengths ......................................................................................................................... 3 - 124 Limitations ....................................................................................................................... 3 - 125 Operational Considerations ............................................................................................. 3 - 125

Multiple PRF Dealiasing Algorithm (MPDA) .................................................... 3 - 126

MPDA is an RPG-based Solution.................................................................................... 3 - 126 Applying MPDA ............................................................................................................... 3 - 126 VCP 121 Considerations ................................................................................................. 3 - 129 MPDA Processing for a Single Range Bin ...................................................................... 3 - 130 MPDA Adaptable Parameters ......................................................................................... 3 - 132 Strengths of MPDA .......................................................................................................... 3 - 133 Limitations of MPDA ........................................................................................................ 3 - 133

Minimizing Range Folding (Objective 4).......................................................... 3 - 134

Minimizing Range Folding ............................................................................................... 3 - 134 MPDA (VCP 121) and Auto PRF..................................................................................... 3 - 137 Mitigation of Data Ambiguities Review Exercises............................................................ 3 - 139

Topic 3, Lesson 6: Precipitation Estimation ........................................ 3 - 143

Precipitation Estimation (instructor guided web module) ............................. 3 - 144 Objectives........................................................................................................... 3 - 144 Reflectivity, Z and Rainfall Rate, R (Objective 1) ............................................ 3 - 144

Reflectivity - Z.................................................................................................................. 3 - 144 Sample Z computation..................................................................................................... 3 - 145 Rainfall Rate - R .............................................................................................................. 3 - 146 Sample R computation .................................................................................................... 3 - 147 Same Z, Different R......................................................................................................... 3 - 147 Same R, Different Z......................................................................................................... 3 - 148

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Distance Learning Operations Course

Interim Summary ............................................................................................................. 3 - 148 WSR-88D Z-R Relationships........................................................................................... 3 - 149

Error Sources in Radar Estimated Rainfall (Objective 2)............................... 3 - 150

Types of errors ................................................................................................................ 3 - 150 Z estimate errors ............................................................................................................. 3 - 150 Z-R relationship errors..................................................................................................... 3 - 152 Below beam effect errors................................................................................................. 3 - 153

Radar Estimates vs. Rain Gages (Objective 3) ............................................... 3 - 154

Scenarios ........................................................................................................................ 3 - 154 Scenario 1 ....................................................................................................................... 3 - 155 Scenario 2 ....................................................................................................................... 3 - 155 Scenario 3 ....................................................................................................................... 3 - 156

Precipitation Processing Subsystem (PPS) (Objective 4) ............................. 3 - 156

Overview ......................................................................................................................... 3 - 157 Enhanced Precipitation Preprocessing (EPRE) .............................................................. 3 - 158 Precipitation Rate Algorithm ............................................................................................ 3 - 167 Precipitation Accumulation Algorithm .............................................................................. 3 - 168 Precipitation Adjustment Algorithm.................................................................................. 3 - 171 Summary ......................................................................................................................... 3 - 174 Precipitation Processing Subsystem - Strengths............................................................. 3 - 174 Precipitation Processing Subsystem - Limitations........................................................... 3 - 174

Snow Accumulation Algorithm (SAA) (Objective 5).......................................3 - 175

References ...................................................................................................................... 3 - 175 SAA Design ..................................................................................................................... 3 - 175 Begin and End of Snowfall Accumulations ...................................................................... 3 - 176 Reset (Begin) the Snow Accumulations .......................................................................... 3 - 177 Converting Reflectivity to the Rate of Snow Water Equivalent ........................................ 3 - 177 Range/Height Correction ................................................................................................. 3 - 179 Snow Ratio ...................................................................................................................... 3 - 180 SAA Adaptable Parameters............................................................................................. 3 - 180 SAA Products .................................................................................................................. 3 - 181

Snow Accumulation Algorithm - Strengths (Objective 5)............................. 3 - 182 Snow Accumulation Algorithm - Limitations (Objective 5) .......................... 3 - 182

Precipitation Estimation Review Exercises...................................................................... 3 - 182

Review Exercises Answer Key ......................................................................... 3 - 185

Signal Processing............................................................................................................ 3 - 185 Base Data Generation ..................................................................................................... 3 - 188 Clutter Suppression ......................................................................................................... 3 - 189 Mitigation of Data Ambiguities ......................................................................................... 3 - 190 Precipitation Estimation .................................................................................................. 3 - 193

3 - 6 Table of Contents

Distance Learning Operations Course

Topic 3, Lesson 1: WSR-88D Fundamentals

Presented by the Warning Decision Training Branch

Distance Learning Operations Course

Topic 3: Principles of Meteorological Doppler Radar

Version: 0609

Distance Learning Operations Course

WSR-88D This lesson will present information that is funda-

Fundamentals (self mental to weather radars in general, such as beam

guided web module)

propagation and the Probert-Jones radar equation. It will also present information that is very specific to the WSR-88D, such as the characteris-

tics of a particular Volume Coverage Pattern

(VCP).

Lesson 1 is unlike any other part of Topic 3, because it is a self guided web module. The remaining web modules, Lessons 2, 3, 4, and 6, are instructor guided, a sequence of annotated slides with accompanying audio for each slide. Lesson 1 has no audio, and it is designed as much for future reference as it is for initial learning.

Lesson 1 is accessed from the DLOC Main Page,



Under Web Modules, you will find a link to Topic 3, Lesson 1, WSR-88D Fundamentals.

The amount of time needed to complete Lesson 1 will vary depending on your experience with the WSR-88D. The average completion time is estimated to be 2 hours.

Objectives 1. Identify the range resolutions and correspond-

ing display ranges for Base Reflectivity, Base Velocity, and Base Spectrum Width.

2. Given dBZ values along a radial at .54 nm resolution, identify which dBZ values would be used to build lower resolution Base Reflectivity products.

3. Given Base Velocity and Spectrum Width values along a radial at .13 nm resolution, identify which Base Velocity and Spectrum Width val-

3 - 8 WSR-88D Fundamentals (self guided web module)

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