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

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

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

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

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

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

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

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

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

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

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:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Capsoni, C., and M. D'Amico, 1998: A physically based radar simulator. J. Atmos. Oceanic Technol., 15, 593- 598. Chandrasekar, V., and V. N. Bringi, 1987: Simulation of radar reflectivity and surface measurements of rainfall. J. Atmos. Oceanic Technol., 4, 464-478. Wood, V. T., and R. A. Brown, 1997: Effects of radar sampling on single-Doppler velocity signatures of mesocyclones and tornadoes. Wea. Forecasting, 12, 928-938. Zrnic, D. S., 1975: Simulation of weatherlike Doppler spectra and signals. J. App. Meteor., 14, 619-620. Questions?