Doppler Radar Technique Research Articles

VHF radar detects oceanic submesoscale vortex along Florida Coast

Escalating national interest in the coastal ocean underscores the need for high‐quality surface current data that can improve our understanding of surface circulation and its impact on societal and environmental issues related to coastal pollution, beach restoration, oil spill mitigation, and coastal air‐sea interaction. Coastal regimes exposed to strong ocean currents,surface waves, and winds during storm conditions may frequently require beach renourishment to restore valuable beaches that are key to local economies. Maintaining water quality is a problem, too, particularly where shipping dominates the traffic in and out of harbors. These environmental issues are increasingly difficult to manage due to evolving oceanic and atmospheric conditions. Inferring evolving spatial patterns of the coastal ocean current fields from single‐point measurements such as moorings or drifters that propagate away from divergent flow regimes is difficult at best. The Doppler radar technique is one approach that effectively measures the evolution of surface current fields in near‐real time.

Acoustic Resonance of the Atmospheric at 3.7 Hz

Vertical propagation of plane acoustic-gravity waves with horizontal wave fronts is discussed using a layer model with realistic temperature structure based on the Cospar International Reference Atmosphere, 1986. Acoustic resonance of a normal mode occurs between the ground and upper mesosphere, at a frequency of 3.64–3.69 mHz. Since acoustic waves with these frequencies are evanescent in the upper mesosphere where the acoustic cutoff is normally around 4.1 mHz, part of the wave energy propagated from below is reflected downward to interfere with the upward-propagating waves, thus causing model resonance. The computed resonant frequency coincides with the lower (3.7 mHz) of the two dominant frequencies found in the Rayleigh wave from the eruptions of El Chichon in 1982 and Mount Pinatubo in 1991. It also agrees with the lower spectral component of the ionospheric infrasonic waves observed by the high-frequency Doppler radar technique in association with severe convective storms below in the troposphere.

A Technique for Detecting a Tropical Cyclone Center Using a Doppler Radar

Abstract A ground-based Doppler radar technique is developed for detecting a tropical cyclone center position. Accurate determination of the cyclone center position, based on Doppler velocity measurements, will become essential for the issuance of hurricane advisories, forecasts, and warnings once a network of WSR-88D Doppler radars is deployed on the United States coastlines, islands, and military bases during the 1990s. This will allow high-resolution detection and tracking of hurricanes nearing land for the first time. Simulated Doppler velocity data, which were reconstructed from wind field data collected by reconnaissance aircraft during Hurricanes Alicia (1983) and Gloria (1985), were used to test the concept of using ground-based Doppler radar data to estimate cyclone center location. The center range and azimuth estimates of a hurricane signature were calculated from the simulated coastal Doppler radar velocity data. Preliminary results indicate that the technique performed well for estimating cen...

Velocity Track Display—A Technique to Extract Real-Time Tropical Cyclone Circulations Using a Single Airborne Doppler Radar

Abstract The concept and formulation of a real-time airborne Doppler radar wind field analysis technique, velocity track display (VTD), is presented. The VTD algorithm is a harmonic analysis method similar to the velocity–azimuth display technique for ground-based radars; however, it is designed to deduce the primary circulation properties of atmospheric vortices such as tropical cyclones. When an aircraft, equipped with a Doppler radar scanning in a track-orthogonal plane, penetrates a cyclonic circulation, VTD decomposes Doppler velocities on cylindrical rings into tangential, radial, and the mean cross-track component of the wind velocity. Obtaining estimates of the vortex circulation requires data from only one aircraft flight leg instead of two in the pseudo-dual Doppler radar method. As a test, the VTD technique was applied to two orthogonal legs (“figure 4” pattern) in Hurricane Gloria (1985). The entire computation was completed about 15 min after the end of each flight leg with little or no human...

A Multibeam Vorticity Measurement Technique for Modular MST Radars

A multibeam Doppler radar technique for atmospheric vorticity measurements is presented and analyzed. The technique is applicable with steerable and modular radars with three or four independent modules centered about the vertices of an equilateral triangle or a square. An accuracy of ∼10−3–10−2 s−1 is predicted in stratospheric vorticity measurements, depending on the available module separations and observation zenith angles.

A Proposed Technique for Diagnosis by Radar of Hurricane Structure

A Doppler radar technique is proposed for remote estimation of hurricane structure by sampling the kinematic properties of the hurricane wind field in a relatively small circular area outside the radius of maximum winds. This technique uses Fourier analysis of the pattern of Doppler velocities measured in a horizontal circle surrounding the radar, following guidelines developed by Browning and Wexler. Two indices, potential-vortex fit (PVF) and radial confluence, are developed as measures of the degree of conformity of the wind field sampled by radar to an idealized Rankine axisymmetric cyclone circulation. The PVF index reveals the extent to which the sampled wind held fits a potential-vortex flow regime, wherein both curvature and speed of the tangential wind component are inversely proportional to distance from a circulation center. The confluence of the radial wind component provides an independent estimate of the curvature of the tangential component. These two indices were measured in Hurricane Gloria (1985) during a period of more than 3 h following its landfall. Values of PVF indicated a weakened circulation during the first half of this period, followed in the latter half by a progressive and rapid decay of the circulation, consistent with other observations. The magnitudes of the radial confluence index, on the other hand, evidently were adversely affected by significant contamination by asymmetries in the hurricane circulation throughout most of the observational period. However, trends in both indices provided an early indication of the deterioration of Hurricane Gloria. Accordingly, it appears worthwhile to seek further evidence of the potential value of this technique as an aid in monitoring hurricane severity.

Three-dimensional single Doppler radar analysis of an occluded front

Single Doppler radar analysis has been applied to an occluded front associated with the last stages of cyclonic activity over the Norrkoping area in Central Sweden. Validation was conducted of the analysis methods, such as reflectivity contouring and wind calculation from Doppler radial velocity using velocity azimuth display (VAD). The structure of the cloud system was identified as composed of a stratocumulus cloud layer, horizontally divided into two sectors of high reflectivity (>20 dBZ), oriented parallel to the surface occluded front, each extending around 80 km W-E and 50 km S-N. Embedded in these two precipitating areas were local regions of very high reflectivity (up to 50 dBZ), indicating the presence of scattered heavy precipitation and showers. The case study represents a test of the capabilities of single Doppler radar analysis techniques to be introduced in the next future into the operative forecasting environment in Italy.

The Effect of Humidity and Bulk Density on Flow Rate Measurements of Rice, Salt and Sugar

The paper consists of flow-rate measurements of solid particulates (rice, salt and sugar) falling freely Under gravity.Microwave Doppler radar has been used as a monitoring device to extract information about the following: (i) variation of Doppler frequency versus humidity, (ii) variations of mass flow rate versus actual pipe diameter, (iii) effect of humidity with measured and calculated mass flow rate, (iv) measurements have been executed using the Doppler radar technique which provides a contactless sensor, does not obstruct the flow field or assist in the formation of blockages.

Radio science and oceanography

The three main radio techniques for remote sensing of the ocean surface, microwave radar, microwave radiometry, and dekametric or HF radar, are surveyed. The generation and characterization of wind waves and swell on the ocean surface, and the first‐order mechanism of Bragg resonant scattering of radio waves by such surfaces are outlined. Doppler HF radar techniques, ground wave and sky wave, developed for utilization of this effect to sense remotely wave, wind direction and surface current velocity are reviewed. Second‐order scattering effects, hydrodynamic and electromagnetic, are also present, and their signatures on the Doppler echo spectrum of an HF radar permit measurement of wave height, wavelength spectrum and directional spectrum. Finally, the scattering mechanisms relevant in satellite‐borne microwave radar are outlined. Bragg resonance occurs with short waves, these being modulated by the longer gravity waves of practical interest. The potential of the radar altimeter, scatterometer and synthetic aperture radar for global ocean surveillance is illustrated by examples from the satellite.

HIGH SPEED VELOCITY LOG

ABSTRACTAdvanced high speed ships (surface effect ships, hydrofoils and air cushioned vehicles) under development will operate at speeds which are considerably higher than conventionally hulled ships. Precise velocity sensing and measuring techniques that provide the required accuracy throughout their operating speed range do not currently exist.This paper will discuss the Navy's development of a High Speed Velocity Log (HSVL), which will provide self contained, two‐axis velocity measurement for these advanced high speed hulls.The system selected by the Navy for an exploratory development program uses microwave doppler radar technology. The paper will discuss reasons why an FM‐CW doppler radar technique was chosen over other candidate technologies. The doppler radar technique involves the transmission of narrow beam radar signals down toward the water surface. Frequency of backscattered energy from the water surface is compared with the frequency of transmission to determine the “doppler” frequency shift from which ship's velocity relative to the water surface is computed.The paper will present test results of the HSVL feasibility model aboard the hydrofoil USS High Point (PCH‐1) and aboard the Amphibious Assault Landing Craft Jeff (B). In addition, a summary of an intensive analysis phase to determine HSVL critical design parameters will be described.

On the vertical‐incidence VHF backscattered power profile from the stratosphere

The slope of vertical incidence VHF backscattered power profiles from the stratosphere can be deduced from atmospheric stability profiles in conjunction with a recently‐developed model of backscattering from horizontally‐stratified refractivity structure in the clear air. The close resemblance of these theoretical profiles to profiles obtained from a number of different locations using the (MST) Doppler radar technique shows that vertical‐incidence VHF backscattering in the stratosphere arises from stable, horizontal laminae of radio refractive index that 1) have horizontal dimensions of many tens of meters, and 2) are distributed randomly throughout the stratosphere.

Automatic control of casting speed in ingot casting

A microwave casting speed meter and the automatic casting speed control system that uses it have been developed for the bottom pouring process of steel ingots. The microwave meter is based on the Doppler radar technique, and a circuit of period measurement and reciprocal calculation has been developed to make its response time faster. Also it has a function to measure cast height. The automatic system can be regarded as a sampled-data system with an adaptive control function. Outlines of the microwave meter, the control circuit and the method of adaptive control are presented. The relationship of the crack appearance to the casting speed is studied, and programmed patterns of the casting speed have been prepared to reduce cracking. The programmed ‘pattern casting’ has been achieved by the automatic control system, and the surface quality of the ingot has been improved.

A new technique for measuring tidal currents by using a two‐site HF Doppler radar system

We have measured surface currents by using a newly developed high‐frequency (HF) Doppler radar technique. The system was operated in lower Cook Inlet, Alaska, in July 1977. During one particular day, July 13, we analyzed the radar data collected every 30 min for 24 hours. By least squares fitting these data to two of the dominant tidal periods, 12.31 and 24.6 hours, we determined the spatial distribution of the tidal currents for each of these two periods. In addition, we determined the spatial distribution of the mean surface currents for this 24‐hour period. Our analysis of this data shows that near Kachemak Bay there is a distinct difference of the east‐west component of tidal flow in comparison with regions further from Kachemak. In addition, we observed longer period components for which we cannot determine the period. These components exhibited gyrelike spatial patterns. Our results demonstrate the use of HF radar techniques for resolving spatial and temporal currents which affect the nearshore environment.

Automatic Control of Casting Speed in Ingot Casting

A microwave casting speed meter and an automatic casting speed control system using it have been developed for the bottom pouring process of steel ingots. The microwave meter is based on the Doppler radar technique, and a circuit of period measurement and reciprocal calculation has been developed to make its response time faster. Also it has a function of cast height determination. The automatic system can be regarded as a sampled-data system with an adaptive control function. Outlines of the microwave meter, the control circuit and the method of adaptive control are presented. The relationship of the crack appearance to the casting speed is studied, and programmed patterns of the casting speed have been prepared to reduce cracking. The “pattern casting” has been realized by the automatic control system, and the surface quality of the ingot has been improved.

Doppler weather radar

The Doppler weather radar and its signals are examined from elementary considerations to show the origin and development of useful weather echo properties such as signal-to-noise ratio (SNR), range correlation, signal statistics, etc. We present a form of the weather radar equation which explicitly shows the echo power loss due to finite receiver bandwidth and how it is related to the range weighting function. Echoes at adjacent range samples have a correlation that depends on receiver bandwidth-transmitter pulsewidth product as well as sample spacing. Stochastic Bragg scatter from clouds is examined, but experimental work is required to determine if this echo power is larger than incoherently scattered power. Section III presents the relation between Doppler power spectrum and the distribution of reflectivity and velocity within a resolution volume. A new formula that relates spectrum width to the shear of radial velocities as well as turbulence, signal decorrelation from antenna rotation, and signal processing biases is presented. The estimation of power spectral moments is reviewed and properties of the most commonly used algorithms are discussed. Section V highlights some of the considerations that need to be made for Doppler radar observation of severe thunderstorms. Echo coherency is shown to limit the pulsed Doppler radar's unambiguous range and velocity measurements. Single and dual Doppler-radar techniques for wind measurements are reviewed. Observations of thunderstorms show tornado cyclones, and clear air measurements in the boundary layer reveal turbulence and waves.

Some New Approaches in Hail Suppression Experiments

It is suggested that progress in hail suppression research requires simultaneous improvements in methods of evaluating seeding effects and in monitoring the physical structure of the hailstorm and the hail growth processes. On this basis a case is made for the extensive use of multiple Doppler radar and chemical tracer techniques.

Examination of a dual wavelength doppler radar technique to measure vertical wind velocity and drop - size distributions

Estimates of drop-size distributions aloft derived from the Doppler velocity spectrum are sensitive to errors in the vertical wind estimate. A technique to deduce vertical velocity from the ratio of power spectra obtained from two vertically pointing radars operating at two different wavelengths is theoretically examined. Using an assumed distribution, ratios of spectral density were computed for clouds composed of water, ice, or water-coated ice, and are presented for a sample of radar wavelengths. These ratios are uniquely related to the vertical wind, and allow its determination independent of an assumed drop-size distribution. Historically, the interdependence between drop-size distribution and vertical wind has limited the accuracy from which either could be deduced. The effect of errors in estimating the temperature of the precipitation and fluctuations in the power spectral estimates are derived for simulated drop-size spectra. Data processing techniques are suggested and the sampling time necessary to estimate the vertical velocity to within 30 cm sec −1 is given.

Multi‐level measurements of turbulence over the sea during the passage of a frontal zone

AbstractA Doppler radar technique originally proposed by Lhermitte (1968) has been used to measure the horizontal components of turbulence simultaneously at closely spaced height intervals from an altitude of 80m to 2500m. The observable range of turbulence scales was between about 200m and 5000m. Observations were made over the sea, with the radar situated on the Isles of Scilly, to minimize the effects of in‐homogeneities in terrain.The measurements reported in this paper were made during the passage of a warm frontal zone with strong surface winds; they show the change with height in the structure of turbulence simultaneously in both the planetary boundary layer and a free shear zone situated some way above it. Below 600m, in the planetary boundary layer, the two horizontal components of turbulence were rather similar in intensity, the total variance of horizontal velocity in the observed spectral range decreasing from 1·7m2s−2 at 80m to less than 0·1m2s−2 at 700m. For much of the observed spectral range the turbulence spectra were of the form kS(k) α k−n, with n decreasing from 1·2 below 300m to 0·7 at 700m. The lapse rate was slightly less than dry adiabatic in the planetary boundary layer with broken cloud above 300m, consistent with slight stability below 300m and some instability above. The decrease in the value of n is thought to have been due to the decrease of stability with height. The spectral scale λm increased with height reaching a value of 1·6km at 900m. Above the boundary layer for most of the time there was a placid layer several hundred metres deep and this was surmounted by a free shear layer in which the variance of velocity increased again to typically 0·5m2s−2. In the free shear layer the horizontal components of turbulence resolved parallel and perpendicular to the local shear vector were rather similar in intensity at scales less than 500m but were markedly unequal at scales between 500m and 2km. This is consistent with the occurrence of Kelvin‐Helmholtz billows with a wavelength of 1 to 2km.The Doppler radar measurements also enabled the vertical flux of horizontal momentum to be calculated. The quantity −u′w′ was found to decrease from about 0·2m2s−2 in the planetary boundary layer to about 0·01m2s−2 in the placid layer, before increasing again to about 0·1m2s−2 in the free shear layer. The energy dissipation rate ϵ was estimated from the turbulence spectra in those cases where the spectral slope n was not greatly different from 2/3. Values of ϵ decreased from 10cm2s−3 at 400m to 2cm2s−3 in the placid layer, before increasing to a second maximum of about 20cm2s−3 in the free shear zone. The rate of mechanical production of turbulence was calculated from the Doppler radar measurements of momentum flux and shear and it was found to vary with height in a rather similar manner to ϵ.

Precipitation Characteristics at Vertical Incidence from Multiple Wavelength Doppler Radars

Abstract A vertically looking, multiple-wavelength Doppler radar technique to estimate vertical velocity, drop size distribution and turbulence is presented. The ratio of the Doppler spectra, corresponding to the drop fall velocities at two different wavelengths, is uniquely related to the ratio of the radar scattering cross sections at the appropriate temperature. These ratios are used to estimate drop fall velocities and therefore drop size distributions and vertical wind. Turbulence, which broadens the velocity power spectrum, can be estimated by deconvolution and the drop size distribution subsequently derived.

Doppler radar identifies birds in flight

Scientists at the National Oceanic and Atmospheric Administration are developing a doppler radar technique for identifying birds in flight.Once perfected, the technique may be applied to airport safety in areas where birds are a hazard. It also may help solve the mysteries of bird migration and other ornithological questions.