Nitin Bharadwaj

The CASA Integrated Project 1 Networked Radar System

Abstract This paper describes the Collaborative Adaptive Sensing of the Atmosphere (CASA) Integrated Project 1 (IP1) weather radar network, the first distributed collaborative adaptive sensing test bed of the Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere. The radar network and radar node hardware and software architectures are described, as well as the different interfaces between the integrated subsystems. The system’s operation and radar node control and weather data flow are explained. The key features of the radar nodes are presented, as well as examples of different data products.

Constructing a Merged Cloud–Precipitation Radar Dataset for Tropical Convective Clouds during the DYNAMO/AMIE Experiment at Addu Atoll

AbstractTo improve understanding of the convective processes key to the Madden–Julian oscillation (MJO) initiation, the Dynamics of the MJO (DYNAMO) and the Atmospheric Radiation Measurement Program (ARM) MJO Investigation Experiment (AMIE) collected 4 months of observations from three radars—the S-band dual-polarization Doppler radar (S-Pol), the C-band Shared Mobile Atmospheric Research and Teaching Radar (SMART-R), and Ka-band ARM zenith radar (KAZR)—along with radiosonde and comprehensive surface meteorological instruments on Addu Atoll, Maldives, in the tropical Indian Ocean. One DYNAMO/AMIE hypothesis suggests that the evolution of shallow and congestus cloud populations is essential to the initiation of the MJO. This study focuses on evaluating the ability of these three radars to document the full spectrum of cloud populations and to construct a merged cloud–precipitation radar dataset that can be used to test this hypothesis. Comparisons between collocated observations from the three radars show ...

Scanning ARM Cloud Radars. Part I: Operational Sampling Strategies

AbstractThe acquisition of scanning cloud radars by the Atmospheric Radiation Measurement (ARM) program and research institutions around the world generates the need for developing operational scan strategies for cloud radars. Here, the first generation of sampling strategies for the scanning ARM cloud radars (SACRs) is presented. These scan strategies are designed to address the scientific objectives of ARM; however, they introduce an initial framework for operational scanning cloud radars. While the weather community uses scan strategies that are based on a sequence of scans at constant elevations, the SACR scan strategies are based on a sequence of scans at constant azimuth. This is attributed to the cloud geometrical properties, which are vastly different from the rain and snow shafts that are the primary targets of precipitation radars; the need to cover the cone of silence; and the scanning limitations of the SACRs. A “cloud surveillance” scan strategy is introduced that is based on a sequence of ho...

Wideband Waveform Design Principles for Solid-State Weather Radars

The use of solid-state transmitters is becoming increasingly viable for atmospheric radars and is a key part of the strategy to realize any dense network of low-powered radars. However, solid-state transmitters have low peak powers and this necessitates the use of pulse compression waveforms. In this paper frequency diversity in a wideband waveform design is proposed to mitigate the low sensitivity of solid-state transmitters. In addition, the waveforms mitigate the range-eclipsing problem associated with long pulse compression. An analysis of the performance of pulse compression using mismatched compression filters designed to minimize sidelobe levels is presented. The impact of the range sidelobe level on the retrieval of Doppler moments is discussed. Realistic simulations are performed based on both the Colorado State University‐University of Chicago‐Illinois State Water Survey (CSU‐CHILL) and the Center for Collaborative Adaptive Sensing of the Atmosphere (CASA) Integrated Project I (IP1) radar data.

Salient features of radar nodes of the first generation NetRad System

The recently established National Science Foundation Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere (CASA) will be deploying the first generation of an automated network of four low-power, short-range, X-band, polarimetric, Doppler radars, known as NetRad, in central Oklahoma in late 2005. This network is developed with the goal of tracking tornadoes with high spatial and temporal resolution as well as mapping severe weather events in the lowest 2 km of the troposphere. Each radar node has been developed to accomplish this system goal through the coordinated interaction with other radars in the network via a real-time, closed-loop software control system. This paper will describe the characteristics of the individual radar nodes in the system, with emphasis on those aspects of the design that lend themselves toward operation as a coordinated network. Calibration results and performance characteristics of the single node radar of the first generation system will also be presented.

Scanning ARM Cloud Radars. Part II: Data Quality Control and Processing

AbstractThe scanning Atmospheric Radiation Measurement (ARM) Program cloud radars (SACRs) are the primary instruments for documenting the four-dimensional structure and evolution of clouds within a 20–30-km radius of the ARM fixed and mobile sites. Here, the postprocessing of the calibrated SACR measurements is discussed. First, a feature mask algorithm that objectively determines the presence of significant radar returns is described. The feature mask algorithm is based on the statistical properties of radar receiver noise. It accounts for atmospheric emission and is applicable even for SACR profiles with few or no signal-free range gates. Using the nearest-in-time atmospheric sounding, the SACR radar reflectivities are corrected for gaseous attenuation (water vapor and oxygen) using a line-by-line absorption model. Despite having a high pulse repetition frequency, the SACR has a narrow Nyquist velocity limit and thus Doppler velocity folding is commonly observed. An unfolding algorithm that makes use of...

Orthogonal Channel Coding for Simultaneous Co- and Cross-Polarization Measurements

Abstract Dual-polarization weather radars typically measure the radar reflectivity at more than one polarization state for transmission and reception. Historically, dual-polarization radars have been operated at copolar and cross-polar states defined with respect to the transmit polarization states. Recently, based on the improved understanding of the propagation properties of electromagnetic waves in precipitation media, the simultaneous transmit and receive (STAR) mode has become common to simplify the hardware. In the STAR mode of operation, horizontal and vertical polarization states are transmitted simultaneously and samples of both horizontal and vertical copolar returns are obtained. A drawback of the current implementation of STAR mode is its inability to measure parameters obtained from cross-polar signals such as linear depolarization ratio (LDR). In this paper, a technique to obtain cross-polar signals with STAR mode waveform is presented. In this technique, the horizontally and vertically pola...

Phase Coding for Range Ambiguity Mitigation in Dual-Polarized Doppler Weather Radars

Abstract This paper evaluates the retrieval of polarimetric variables when phase-coded waveforms are employed to suppress range overlaid echoes. A phase-coded waveform tags transmitted pulses with a phase code and then decodes the received signal to separate the overlaid echoes. Two methods suggested for separating overlaid echoes use random and systematic phase-coding techniques. In this paper, random phase and systematic phase-coded waveforms are evaluated for dual-polarized operation. The random phased-coded and systematic phase-coded waveforms are known to provide fairly good estimates of the Doppler spectral moments. This paper presents results at S band to quantify the performance of phase-coded waveform in retrieving polarimetric variables. It is shown that the polarimetric variables for both strong and weak trip echoes are estimated with acceptable accuracy.

Signal Processing System for the CASA Integrated Project I Radars

Abstract This paper describes the waveform design space and signal processing system for dual-polarization Doppler weather radar operating at X band. The performance of the waveforms is presented with ground clutter suppression capability and mitigation of range–velocity ambiguity. The operational waveform is designed based on operational requirements and system/hardware requirements. A dual–Pulse Repetition Frequency (PRF) waveform was developed and implemented for the first generation X-band radars deployed by the Center for Collaborative Adaptive Sensing of the Atmosphere (CASA). This paper presents an evaluation of the performance of the waveforms based on simulations and data collected by the first-generation CASA radars during operations.

Development and Applications of ARM Millimeter-Wavelength Cloud Radars

PAVLOS KOLLIAS, EUGENE E. CLOTHIAUX, THOMAS P. ACKERMAN, BRUCE A. ALBRECHT, KEVIN B. WIDENER, KEN P. MORAN, EDWARD P. LUKE, KAREN L. JOHNSON, NITIN BHARADWAJ, JAMES B. MEAD, MARK A. MILLER, JOHANNES VERLINDE, ROGER T. MARCHAND, AND GERALD G. MACE McGill University, Montreal, Quebec, Canada The Pennsylvania State University, University Park, Pennsylvania University of Washington, Seattle, Washington University of Miami, Miami, Florida Pacific Northwest National Laboratory, Richland, Washington National Oceanic and Atmospheric Administration, Boulder, Colorado Brookhaven National Laboratory, Upton, New York ProSensing, Inc., Amherst, Massachusetts Rutgers, The State University of New Jersey, New Brunswick, New Jersey University of Utah, Salt Lake City, Utah