1. A Moment Radar Data Emulator: The Current Progress and Future Direction
Ryan M. May

2. Motivation
Create tool that generates radar moment data for a given set of radar operating parameters
Useful for:
Radar system design
Scanning strategy design
Algorithm development
Retrieval technique evaluation

3. Radar Configuration Wavelength Location Transmit Power Antenna Gain
Antenna Beamwidth
Noise Threshold
Pulse Length
PRF
Pulses per Radial
Rotation Rate
Gate Length
Scan Angles

4. Capabilities Azimuthal Resolution Range Resolution Attenuation
Range Aliasing
Velocity Aliasing
Anomalous Propagation
Antenna Sidelobes

5. Scattering
Currently, the Rayleigh approximation is used for scattering:
Rain is assumed to have a Marshall-Palmer distribution
Cloud droplets are assumed to be monodisperse

6. Emulator Design
A “pulse” is propagated through the model’s numerical output grid along the current pointing angle
This pulse is subdivided into many small, individual elements
Each element is assigned values for reflectivity, radial velocity, and attenuation factor from the model grid, using nearest neighbor sampling

7. Emulator Design (cont.)
Representation of segmented pulse being matched to model grid field

8. Emulator Design (cont.)
At a given instant, two pulses are being used, one at a range less than Ra and one at a range greater than Ra, allowing for the simulation of 2nd trip echoes
For every range gate along the propagation path, the pulses are sampled to produce a value of power, Doppler velocity, and velocity variance

9. Emulator Design (cont.)
Power is calculated as:
Doppler velocity is the power-weighted average of all velocities for all pulse elements
The velocity variance for the pulse is the power-weighted variance of velocities for all pulse elements

10. Emulator Design (cont.)
When the specified number of pulses for a radial have been sampled, a radial of data is generated
Returned power is the average power for all pulses
Doppler velocity is the power-weighted average velocity for all pulses
Spectrum width is the power-weighted velocity variance for all pulses

11. Emulator Design (cont.)
At this point, the velocity is forced to a value within the Nyquist co-interval, simulating velocity aliasing
Also, equivalent radar reflectivity factor is calculated from the returned power as:

12. Simulation Characteristics
Simulation created using the Advanced Regional Prediction System (ARPS)
Horizontal grid resolution: 50m
Stretched vertical grid (~18m at surface)
Warm rain precipitation microphysics
Produces a 200m diameter tornado with a 160 m/s change in velocity across the vortex

13. ARPS Simulation Vector Velocity, Rain Water Mixing Ratio, and Total Buoyancy

14. Capabilities – Radar Characteristics
Exp. λ
(cm)
Beamwidth
(deg)
PRF
(Hz)
Pulse Length
(μs)
Rot. Rate
(deg s-1)
Pulses Per Rad.
Gate Length
(m)
control 10 1
1500
1.5 20 75
250 OS 15 50 GS
.75
125 BW 2 NY
1000 X 3 ST

15. Examples – 10cm, 1o Beamwidth
Equivalent Reflectivity Factor
Returned Power
Doppler Velocity
Spectrum Width

16. Examples – Azimuthal Oversampling
CONTROL Equivalent Reflectivity Factor
CONTROL Doppler Velocity
OVERSAMPLED Equivalent Reflectivity Factor
OVERSAMPLED Doppler Velocity

17. Examples – 125m Gate Spacing
CONTROL Equivalent Reflectivity Factor
CONTROL Doppler Velocity
125M GATE SPACING Doppler Velocity
125M GATE SPACING Equivalent Reflectivity Factor

18. Examples – 2o Beamwidth Equivalent Reflectivity Factor (original)
Doppler Velocity (original)
Equivalent Reflectivity Factor (2o Beamwidth)
Doppler Velocity (2o Beamwidth)

19. Examples – Low PRF Equivalent Reflectivity Factor Returned Power
Doppler Velocity
Spectrum Width

20. Examples – X-band (3cm) Equivalent Reflectivity Factor Returned Power
Doppler Velocity
Spectrum Width

21. Returned Power Difference (Original – X-band)
Examples – X-band (3cm)
Returned Power Difference (Original – X-band)

22. Examples – 2nd Trip Echoes
Equivalent Reflectivity Factor
Returned Power
Doppler Velocity
Spectrum Width

23. Recent Progress Bugfixing Optimization
Software debugging packages (like gdb) are extremely helpful
Optimization
Run time for 88d-type run decreased from 10 hours for a sector to 2 hours
Code profilers are your friend!
Memory usage decreased from 3.9 GB to 1.7 GB
Volume scan time down to 1 day from 2 weeks

24. Recent Progress (cont.)
New scattering code is almost ready
T-matrix vs. Mie

25. Recent Progress (cont.)
Comparison of equivalent radar reflectivity and attenuation coefficient for different scattering models

26. Recent Progress (cont.)
Manuscript submitted to JTECH
Accepted with (major) revisions
Two major complaints
Rayleigh approximation used for attenuation
No ‘signal’ fluctuations due to realignment of scatterers or noise

27. Near Term Developments and Studies
Finish incorporate new scattering code
Continue examining the detectability of tornadoes -- next using objective algorithms
Evaluate scanning impacts on quality of dual Doppler analysis
Phased Array Antenna
Some necessary software upgrades
Include storm evolution

28. Capsoni, C., and M. D'Amico, 1998: A physically based radar simulator. J. Atmos. Oceanic Technol., 15,
Chandrasekar, V., and V. N. Bringi, 1987: Simulation of radar reflectivity and surface measurements of rainfall. J. Atmos. Oceanic Technol., 4,
Wood, V. T., and R. A. Brown, 1997: Effects of radar sampling on single-Doppler velocity signatures of mesocyclones and tornadoes. Wea. Forecasting, 12,
Zrnic, D. S., 1975: Simulation of weatherlike Doppler spectra and signals. J. App. Meteor., 14,
Questions?