Robert M. Beauchamp

Salient features of the dual‐frequency, dual‐polarized, Doppler radar for remote sensing of precipitation

The global precipitation measurement (GPM) mission is an international satellite mission to obtain accurate observations of precipitation on a global scale every 3 h. Its (GPM) core satellite was launched on 27 February 2014 with two science instruments: the microwave imager and the dual-frequency precipitation radar. Ground validation is an integral part of the GPM mission where instruments are deployed to complement and correlate with spacecraft instruments. The dual-frequency, dual-polarization, Doppler radar (D3R) is a critical ground validation instrument that was developed for the GPM program. This paper describes the salient features of the D3R in the context of the GPM ground validation mission. The engineering and architectural overview of the radar is described, and observations from successful GPM ground validation field experiments are presented.

Overview of the D3R Observations during the IFloodS Field Experiment with Emphasis on Rainfall Mapping and Microphysics

AbstractThe NASA dual-frequency, dual-polarization Doppler radar (D3R) was deployed as part of the GPM Iowa Flood Studies (IFloodS) ground validation field campaign from 1 May through 15 June 2013. The D3R participated in a multi-instrument targeted investigation of convective initiation and hydrological response in the midwestern United States. An overview of the D3R’s calibration and observations is presented. A method for attenuation correction of Ka-band observations using Ku-band results is introduced. Dual-frequency ratio estimates in stratiform rain and ice are presented and compared with theoretical values. Ku-band quantitative precipitation estimation results are validated against IFloodS ground instruments.

Dual-Polarization Radar Characteristics of Wind Turbines With Ground Clutter and Precipitation

The demand for renewable power production has fostered an exponential increase in the size and number of wind turbines. This expanding source of power generation is sometimes at odds with maintaining the effective operation of radar systems in air traffic control, defense, weather prediction, and severe-storm-tracking applications. With the recent upgrade of the NEXRAD weather radar system to enable dual-polarization observations, a dual-polarization characterization effort of wind turbines is warranted. Focusing on weather radar applications, a characterization of ground clutter, precipitation, and wind turbines is presented here using a consistent unified treatment. This characterization effort directly compares the dual-polarization radar signatures of these three classes of scatterers. The physical characteristics of wind turbines (particularly their cyclostationary behavior) are exploited to identify unique dual-polarization radar signatures.

Suppressing Wind Turbine Signatures in Weather Radar Observations

Unwanted radar echoes, colloquially referred to as “clutter,” impede the mission effectiveness of radar systems. Depending on radar’s application, clutter examples can include weather, buildings, vegetation, and more. Techniques to mitigate clutter and improve the performance of radar systems are continuously being developed and refined. In this paper, wind turbines used for commercial power generation, which present a Doppler velocity signature that is time-varying, are considered a source of radar clutter. A wind turbine clutter mitigation technique is developed for fixed-pointing weather radar applications, approximating the turbine’s radar signature as a cyclostationary process. The cyclostationary model for the wind turbine and the suppression technique is then validated using observations of wind turbines and precipitation.

Deployment and performance of the NASA D3R during the GPM OLYMPEx field campaign

The NASA D3R was successfully deployed and operated throughout the NASA OLYMPEx field campaign. A differential phase based attenuation correction technique has been implemented for D3R observations. Hydrometeor classification has been demonstrated for five distinct classes using Ku-band observations of both convection and stratiform rain. The stratiform rain hydrometeor classification is compared against LDR observations and shows good agreement in identification of mixed-phase hydrometeors in the melting layer.

Vertical Air Motions and Raindrop Size Distributions Estimated Using Mean Doppler Velocity Difference From 3- and 35-GHz Vertically Pointing Radars

Vertical profiles of vertical air motion and raindrop size distributions (DSDs) within stratiform rain are estimated using two collocated vertically pointing radars (VPRs) operating at 3 and 35 GHz. Different raindrop backscattering cross sections occur at 3 and 35 GHz with Rayleigh scattering occurring for all raindrops at 3 GHz and Mie scattering occurring for larger raindrops at 35 GHz. This frequency-dependent backscattering cross section causes differently shaped reflectivity-weighted Doppler velocity spectra leading to radar transmit frequency-dependent radar moments of intrinsic reflectivity factor, mean Doppler velocity, and spectrum variance. The retrieval method described herein uses four radar moments as inputs to retrieve four outputs at each height within a precipitation column. The inputs include 3-GHz VPR mean Doppler velocity and unattenuated reflectivity factor and 35-GHz VPR mean Doppler velocity and spectrum variance. The outputs include vertical air motion and three parameters of a gamma-shaped DSD. To account for different VPR sample volumes, radar observations were accumulated over 45 s and over several range gates to represent time-space scales larger than either VPR sample volumes. Observed variability over this common time-space scale is used to estimate retrieval uncertainties. The retrieved air motions and DSD parameters compare well against retrievals from a collocated 449-MHz VPR that estimated air motions from Bragg scattering signals and DSD parameters from Rayleigh scattering signals.

Robust Linear Depolarization Ratio Estimation for Dual-Polarization Weather Radar

Linear depolarization ratio (LDR) is often difficult to measure in low and moderate signal-to-noise ratio conditions because the cross-polar echo power is typically two to three orders of magnitude weaker than the copolar echo power. For radars operating at attenuating frequencies such as X-, Ku-, and Ka-bands, differential attenuation must be accounted for to accurately estimate the LDR. A method for robust estimation of the LDR is introduced and evaluated that addresses both of these issues. In practice, the “enhanced” LDR offers robust LDR estimation over current estimation methods. The enhanced LDR is insensitive to noise, radar calibration error, and path-integrated attenuation. The proposed estimator is experimentally validated using Ku-band observations from the National Aeronautics and Space Administration dual-frequency dual-polarization Doppler radar (D3R).

Deployment and performance of NASA D3R during GPM IPHEx field campaign

In order to investigate how well observations from precipitation-monitoring satellites match up to the best estimate of the true precipitation measured at ground level and how to use the collected precipitation data to evaluate models that describe and predict the hydrology, the Integrated Precipitation and Hydrology Experiment (IPHEx) was conducted in the southern Appalachian Mountains in the eastern United States from May 1 to June 15, 2014. The NASA dual-frequency dual-polarization Doppler radar (D3R), co-located with NASA NPOL radar, was deployed as part of the IPHEx field campaign to characterize precipitation properties at Ku- and Ka-band frequencies. This paper presents the deployment and performance of D3R during the IPHEx field experiment. Sample observations will be presented, with particular attention paid to cross-comparison between D3R and NPOL.

Deployment and performance of the NASA D3R during GPM IFloods field campaign

The Iowa Flood Studies (IFloodS) field experiment was conducted to better understand the strengths and limitations of Global Precipitation Measurement (GPM) mission satellite products in the context of hydrologic applications. The NASA dual-frequency dual-polarization Doppler radar (D3R), designed as part of the GPM ground validation program, participated in the IFloodS field campaign to characterize precipitation properties at Ku- and Ka-band frequencies. This paper presents the deployment of the D3R and summarizes the D3R observations during the IFloodS field campaign. The quality of the D3R measurements is evaluated by comparing with the NASA NPOL S-band radar observations. In addition, the capability for rainfall estimation using the D3R is also described and validated using ground gauge measurements.

Characterization and Modeling of the Wind Turbine Radar Signature Using Turbine State Telemetry

Wind turbine observations and characterization efforts have treated the wind turbine as a noncooperative target. Similarly, suppression of the turbine’s radar signature has been considered without the aid of state information from the wind turbine under observation. In this paper, X-band radar observations of a utility-scale wind turbine, with detailed turbine state telemetry, are investigated. From scattering theory, the wind turbine’s physical structure has a deterministic radar cross section for a given observation geometry. Using the telemetry, the variation in the turbine’s signature is considered over a range of operating states. The deterministic nature of a turbine’s signature is demonstrated from radar observations, and a model is developed to isolate it. The turbine’s radar signature, as it relates to changes in the operating state, is discussed with the intent of enabling future suppression techniques.