Multi-PRI Signal Processing for the Terminal Doppler Weather Radar. Part I: Clutter Filtering

Multiple pulse repetition interval (multi-PRI) transmission is part of an adaptive signal transmission and processing algorithm being developed to aggressively combat range–velocity ambiguity in weather radars. In the past, operational use of multi-PRI pulse trains has been hampered due to the difficulty in clutter filtering. This paper presents finite impulse response clutter filter designs for multi-PRI signals with excellent magnitude and phase responses. These filters provide strong suppression for use on low-elevation scans and yield low biases of velocity estimates so that accurate velocity dealiasing is possible. Specifically, the filters are designed for use in the Terminal Doppler Weather Radar (TDWR) and are shown to meet base data bias requirements equivalent to the Federal Aviation Administration’s specifications for the current TDWR clutter filters. Also an adaptive filter selection algorithm is proposed that bases its decision on clutter power estimated during an initial long-PRI surveillance scan. Simulations show that this adaptive algorithm yields satisfactory biases for reflectivity, velocity, and spectral width. Implementation of such a scheme would enable automatic elimination of anomalous propagation signals and constant adjustment to evolving ground clutter conditions, an improvement over the current TDWR clutter filtering system.United States. Federal Aviation Administration (contract F19628-00-C-0002

Airborne Doppler Radar Observations of PyroCu/Cb Plume Kinematics and Thermodynamics During the 2016 Pioneer Fire

During a period of explosive growth of the Pioneer Fire (Idaho, August 2016), deep pyroconvective plumes were sampled by aircraft. The research aircraft was equipped with both remote sensing and in situ instrumentation, including a W-Band Doppler radar which provided high-resolution vertical velocity retrievals from within the developing pyrocumulus. Being the first direct observations of vertical velocity within a pyrocumulus cloud, they have provided unique insights into the dynamical processes governing pyroconvective environments, with important implications for the fire modeling community. The observations were quality-controlled and corrected for issues such as Doppler velocity aliasing, and the plume’s kinematic structure was examined and contextualized using flight-level and surface thermodynamic data collected by the Boise National Weather Service, RAWS observations, and NEXRAD radar-derived plume echo tops. The analyses indicated an extreme pyroconvective environment, with updrafts approaching 60 m s-1 several kilometers above ground level. Interestingly, the observations yielded no secondary peak in vertical velocity aloft linked to latent heat release from condensation. Moreover, updraft magnitude was found to increase with height above the surface and below the condensation level. A wide updraft core acting to isolate the plume center from lateral entrainment processes is hypothesized as a possible explanation for the observed characteristics of the vertical velocity profiles

Applied Radar Meteorology

This is a textbook focused on operational and other aspects of applied radar meteorology. Its primary purpose is to serve as a text for upper-level undergraduates and graduate students studying meteorology, who wish to work as professional operational meteorologists in the U.S. National Weather Service or the Air Force Weather Agency. In addition to a detailed description of operational weather radar systems operating in the United States, this text also provides a brief historical overview of the subject as well as a basic review of the physics of electromagnetic radiation and other theoretical aspects of weather radar. The last two chapters discuss a sample of other radar systems (such as the Doppler on Wheels and the Canadian and European operational networks), and future directions of weather radar, including its use as an input for high-resolution, rapid refresh computer models

Storm microphysics and kinematics at the ARM-SGP site using dual polarized radar observations at multiple frequencies

2014 Fall.Includes bibliographical references.This research utilizes observations from the Atmospheric Radiation Measurement (ARM) Climate Research Facility at the Southern Great Plains location to investigate the kinematic and microphysical processes present in various types of weather systems. The majority of the data used was collected during the Mid-latitude Continental Convective Cloud Experiment (MC3E), and utilizes the network of scanning radars to arrive at a multi-Doppler wind retrieval and is compared to vertical wind measurements from a centrally located profiling radar. Microphysical compositions of the storms are analyzed using a multi-wavelength hydrometeor identification algorithm utilizing the strengths of each of the radar wavelengths available (X, C, S). When available, a comparison is done between observational analysis and simulated model output from the Weather Research Forecasting model with Spectral-bin Microphysics (WRF-SBM) using bulk statistics to look at reflectivity, vertical motions, and microphysics

Wind Retrieval Algorithms for the IWRAP and HIWRAP Airborne Doppler Radars with Applications to Hurricanes

Algorithms for the retrieval of atmospheric winds in precipitating systems from downward-pointing, conically-scanning airborne Doppler radars are presented. The focus in the paper is on two radars: the Imaging Wind and Rain Airborne Profiler(IWRAP) and the High-altitude IWRAP (HIWRAP). The IWRAP is a dual-frequency (Cand Ku band), multi-beam (incidence angles of 30 50) system that flies on the NOAAWP-3D aircraft at altitudes of 2-4 km. The HIWRAP is a dual-frequency (Ku and Kaband), dual-beam (incidence angles of 30 and 40) system that flies on the NASA Global Hawk aircraft at altitudes of 18-20 km. Retrievals of the three Cartesian wind components over the entire radar sampling volume are described, which can be determined using either a traditional least squares or variational solution procedure. The random errors in the retrievals are evaluated using both an error propagation analysis and a numerical simulation of a hurricane. These analyses show that the vertical and along-track wind errors have strong across-track dependence with values of 0.25 m s-1 at nadir to 2.0 m s-1 and 1.0 m s-1 at the swath edges, respectively. The across-track wind errors also have across-track structure and are on average, 3.0 3.5 m s-1 or 10 of the hurricane wind speed. For typical rotated figure four flight patterns through hurricanes, the zonal and meridional wind speed errors are 2 3 m s-1.Examples of measured data retrievals from IWRAP during an eyewall replacement cycle in Hurricane Isabel (2003) and from HIWRAP during the development of Tropical Storm Matthew (2010) are shown

EXPLORING THE CAPABILITIES OF THE AGILE BEAM PHASED ARRAY WEATHER RADAR

Weather radar researchers have long been eager to exploit the capabilities of phased array antennas, but high cost and technical complexity have postponed their widespread use in radar meteorology. With the aging of the current network of operational Doppler weather radars, the possibility of replacing them with phased array radars has renewed interest in applying this technology to weather radar research. The main focus of this research is the "agile beam" or electronic scanning capability of phased array antennas. Three research areas that take advantage of this agile beam capability are addressed in this work: spectral characterization of ground clutter with phased array radar data, staggered PRT beam multiplexing (SBMX), and rapid weather detection. Most of the research on ground clutter filtering has been applied to rotating antennas, but the agile beam capability of the phased array allows the collection of data with a stationary antenna. Studying the characteristics of ground clutter spectra for a stationary antenna could lead to new techniques and improvements for clutter filtering with phased arrays. Ground clutter data were collected under varying wind conditions, foliage levels, and terrain types. The shapes of the ground clutter spectra are then characterized using a novel quadratic clutter model, and the dependence of the model parameters on different conditions is explored. The model is then applied to the examination of clutter width and the time series simulation of ground clutter. SBMX takes advantage of the ability of the phased array to scan the beam in a different direction on a pulse-to-pulse basis which can save time by collecting samples that are nearly independent. SBMX is compared to two conventional scanning strategies to assess its performance using both simulations and real data. It performs well at high signal-to-noise ratios and narrow spectrum widths, but the staggered PRT strategy performs comparably to SBMX, takes less time, and has proven strategies for clutter filtering. The last area of research, rapid weather detection, looks at the use of beam multiplexing to improve the detection of weather signatures. A simple beam multiplexing strategy outperforms a contiguous pulse strategy because the probability of detection of weather signatures is constant for beam multiplexing while the probability of detection for contiguous pulses decreases at narrow spectrum widths. The effects of beam broadening on the scanning strategies are also examined

A MOBILE RADAR BASED CLIMATOLOGY OF SUPERCELL TORNADO STRUCTURES AND DYNAMICS

Fine-scale-resolution mobile radar observations of supercell tornadoes have been collected by the Doppler On Wheels (DOWs) platform between 1995 and 2010. The result of this ongoing effort is a large observational database spanning over 170 separate supercell tornadoes with a typical data spacing of O(50 m X 50 m X 50 m), updates every O(60 s) and measurements within 20 m of the surface extending to several km above the ground. The data used in this study span 1995-2001 and 69 tornadoes along with about four selected tornadoes from 2003-2004.Stemming from this observational database is an effort to characterize both the structure and dynamics of the high wind speed environments in and near supercell tornadoes. To this end, a suite of algorithms was developed for and applied to the DOW radar observations for quality assurance along with detection, tracking and extraction of attributes associated with the tornadoes.The integration of observations across tornado cases in the database produced tornado size and intensity distributions revealing a preferred scale and amplitude for tornadoes produced from mesocyclones of supercell thunderstorms while exhibiting a weak negative correlation between the horizontal scale of a tornado vortex core and the peak intensity. Two horizontal scales are apparent in the clustering of intensity observations with the strongest tornadoes on the smaller scale. The observed intensity distribution is contrasted with traditional damage derived intensity estimates of the same tornadoes from a storm report database to highlight the existing low-bias in supercell tornado intensity estimates.The vertical structure of the DOW-observed tornadoes is characterized by a much larger variance of near-surface (within 200 m of the surface) tornado wind speeds compared to those associated with the larger scale mesocyclonic flow aloft (over 1 km above the surface) often observed by operational radars. Time and tornado averaged vertical profiles of intensity exhibit a nearly constant value with height in the lowest several hundred meters. Horizontal profiles of velocity and vorticity show a bias towards divergent tornado cores with vertical vorticity maxima in the interior of the tornado core and a departure from solid body rotation.The evolution of vortex-scale vorticity in most of the tornadogenesis cases also revealed a dominant mode of simultaneous scale contraction through the lowest 1 km layer which has implications for the vertical structure of forcing associated with mesocyclone-associated tornado formation. Layer-averaged low-level (within 500 m of the surface) horizontal angular momentum profiles in weak and the decaying stage of strong tornadoes appear to have non-contracted angular momentum values remaining at larger radii but are removed through lateral advection away from the tornado and/or divergent flow