High-power Radar Research Articles

Identification of preferred areas of shower development by means of high power radar

Identification of preferred areas of shower development by means of high power radar

Observations of Lee waves by high-power radar

A very high-sensitivity 107 mm radar has been brought into operation for meteorological studies of airflow within the optically clear (or cloudy) atmosphere. One application of this radar has been to observe the detailed three-dimensional structure of lee waves, using backscatter from both refractive index inhomogeneities and cirrus ‘clouds’ as means of tracing the pattern of airflow. This paper presents case studies showing how the radar has revealed the structure of lee waves downwind from the Welsh mountains. One of the case studies illustrates a steady-state wave pattern, another illustrates an unsteady pattern with waves varying in orientation and wavelength, another illustrates a strongly damped wave pattern, and a final one illustrates two families of waves co-existing at different altitudes. The radar method is shown to provide a direct and elegant technique for measuring lee wave properties. Although it depends on the presence of naturally occurring targets to trace the airflow pattern, such targets are found to be abundant in situations of strong lee wave activity.

Identification of preferred areas of shower development by means of high power radar

AbstractA high‐power, high‐gain radar has been used to investigate clear air echoes on days when surface heating produced low‐level convection. The echoes were from irregular refractive index gradients produced primarily by gradients of water vapour density of small scale (5 cm). It was observed that the height to which the convection extended was revealed by an almost continuous layer of echo. This layer was perturbed on a scale of kilometres by individual convective elements; in addition Areas of Deeper Convection (termed ADCs) some tens of kilometres across occurred. These features are described in this paper. Individual ADCs were identifiable as entities for several hours, and, on the one occasion when reliable movements could be determined, they travelled with the low‐level wind. When the vertical structure of the atmosphere was such that showers occurred, they developed only within ADCs. Evidently the showers occurred in clusters because of the pre‐existing structure of the convective layer and not because individual showers modified their near environment.On two of the four occasions studied the ADCs could be related directly to topographical features. In one case of negligible wind an ADC developed and remained close to hills; on another occasion a plume‐like area of deeper convection over 100 km long appeared to stream away from high ground. More generally, however, advection of ADCs masked possible topographical influences.It is suggested that by using a high power radar to identify ADCs it may be possible to forecast the location of outbreaks of showers and thunderstorms more precisely than is possible at present. Further lines of research are also proposed.

Identification of preferred areas of shower development by means of high power radar

Identification of preferred areas of shower development by means of high power radar

Structure of the atmosphere in the vicinity of large-amplitude Kelvin-Helmholtz billows

Data are presented for 17 separate occurrences of Kelvin-Helmholtz billows in the upper troposphere for which the crest-to-trough amplitude exceeded 200 m. The billows were detected in clear air by means of high-power radar. The associated mesoscale patterns of static stability, vertical wind shear, and Richardson number have been derived from sequences of hourly radiosondes tracked by precision radar. Every occurrence of billows was found to be closely associated with well-defined, local, wind-shear maxima. In some cases the shear was as strong as 9 m s−1 per 200 m. The minimum value of the Richardson number when evaluated over layers 200 m deep was usually found to be in the range 0.15–0.3.

High-power radar for meteorological stuides in clear air

A very high-sensitivity S band radar capable of detecting targets with radar cross-section of 5 × 10−10 m2 of reflectivities of 2 × 10−15 m−1 at a range of 10km has recently been brought into operation for meteorological studies of the clear atmosphere. The paper outlines the constraints set by the meterological requirements, and describes the radar which has been assembled to meet them. Examples are presented of clear-air echoes obtained both from extensive horizontal layers at hieghts up to 3 km, and also from high-altitude clear-air turbulence.

Simultaneous Measurements of Clear Air Turbulence at the Tropopause by High-power Radar and Instrumented Aircraft

Large amplitude Kelvin-Helmholtz billows observed by radar at a height of almost 11 km are shown to have been associated with clear air turbulence which produced a vertical aircraft acceleration of 0.65g.

The Dynamics of the Convective Process in Clear Air as Seen by Radar

Abstract Sensitive, high-powered radar have been used to study the dynamics of the convective process in optically clear air. Various stages in the development of the convective field have been identified on the basis of distinctive radar patterns of the cells. The characteristics of the convective field as a whole and the individual cells making up the field during each stage are discussed. During the initial formation stage, the radar returns are diffuse and mottled. Following the destruction of the surface inversion, the first doughnut or ring-shaped radar returns appear which mark the beginning of the field growth stage. At the onset of this stage, the cells are small, around 100-200 m in diameter. As time progresses, the height of the convective field increase at a rate of 4.5-6 m min− 1, while the convective cells themselves grow to several thousand meters in diameter. Based on a comparison of the radar patterns with previous aircraft measurements of the physical properties of convective cells, it i...

Observations of Clear Air Turbulence by High Power Radar

Clear air turbulence is a hazard to aviation and is thought to have important effects on atmospheric dynamics. This article describes the structure and evolution of clear air turbulence at high altitudes as revealed by a high power radar and vertical soundings of wind and temperature.

The use of amplitrons as microwave amplifiers in high power radar systems with frequency agility†

ABSTRACT There are two important problems that arise in the use of amplitrons, as broadband microwave amplifiers in high power radar systems with frequency agility. The first one is to modify the conventional high vacuum tube modulator to obtain proper operation with good efficiency in case of very high power levels. The second one is to modify the modulator circuit by increasing its output impodance and thus limiting the poak current variations in the transmitted frequency band. In this paper analyses are made of both these problems, some practical results are given, and the implication in actual transmitter design is examined.

High Power Radar for Ionospheric Research

A new high power radar at Malvern is being used to investigate the ionosphere by the incoherent scatter technique.

High-power surviellance radar

High-power surviellance radar

Radar EMC in the Space Age

This paper is based on a recent study-in-depth of the current radar situation in the United States. It is intended here to define, on the basis of the data offered by this study, radar's contribution to the electromagnetic compatibility (EMC) environment of today and for the next decade. It will be shown that the current maximum in radar power output, about 200 megawatts peak, is constrained by a number of technological factors to remain quite static throughout this period; what will increase, and in rapid fashion, is the actual number of these high-powered radiators. What this will mean to the space-age EMC engineer will be determined by blocking out the dimensions of the current problem, and then extrapolating to a point, say, ten years hence by the geographical multiplication suggested. It will be shown first that the present situation wrought by high-power radar is not encouraging from the EMC standpoint, and, secondly, that it should be the mission of EMC agents to arrest today's problems and then outpace the predictable increase in these offenders. The prediction is that they will; the Herculean efforts of the early EMC pioneers have given us today a highly receptive audience, in government and in industry. In the radar area the cooperation is better than average; a healthy awareness of problems of interference and their ramifications is in evidence and well documented.

A pulse compression predistortion function for efficient sidelobe reduction in a high-power radar

The successful application of pulse compression techniques depends largely on reduction of the range sidelobes associated with the compressed pulse waveform. It is shown that the calculation of sidelobe levels in previously published data is not exact when low sidelobes are called for, since the effects of spectrum amplitude ripple in contributing to the range sidelobes have either been ignored or not stated. This paper presents more recent information on this subject, introducing a model of the Fresnel spectrum that permits a more accurate calculation of the compressed pulse sidelobe structure. Additional spectrum-associated paired-echo range sidelobes are predicted as a result of the model, and are observed in practice, having peak values up to 15 db larger than those derived on the basis of the idealized spectrum assumed in earlier studies. It is shown experimentally that elimination of the spectrum amplitude ripple results in removal of these paired-echo sidelobes, thus allowing more efficient use of the signal energy when low side-lobe levels are required. A predistorted linear FM pulse compression signal is presented as a realizable means for exerting control over the spectrum function. This new pulse compression technique does not require pulse envelope or rise-time shaping at the transmitter, and thus has application to high-power systems. Experimental waveforms illustrate the reduction of the spectrum-associated paired-echo sidelobes with the modified linear FM signal, and also show that the remaining range sidelobes do not appreciably increase as a function of Doppler shift.

Radio-frequency leakage into missiles

Missile functions are often initiated by the detonation, upon command, from either a wire or radio circuit, of sensitive electroexplosive devices. The possibility exists of inadvertent detonation of these devices caused by the leakage of radio-frequency energy into the missile from high-power radar or communications facilities. This paper treats the idealized problem of RF energy leakage through a slot in an infinite cylinder as a perturbation on the scattering problem for the same object with no slot. It is shown that interior response depends on three factors: the exterior skin current density from the scattering problem, the transmitting admittance of the slot, and an eigenfunction expansion of the interior field when unit voltage is impressed across the slot. It is then proposed that the form of this solution may be applicable and conceptually useful in treating other problems either theoretically or experimentally.

A Radar Study of Altocumulus cloud using 3-cm High Power Radar CPS-9

Radar study of clouds has mostly been confined to that of convective clouds or precipitation-producing stratiform clouds. No such study appears to have been made of the non-precipitating clouds like altocumulus.
 
 The high power radar CPS-9 at Safdarjung, New Delhi, has been receiving radar echoes from altocumulus clouds of cloudlet type and these have been under study. Two examples are presented here and discussed. Based on the radar parameters, the order of the smallest droplet size in altocumulus has been calculated and is found to be of the order 6u-8u and to be fairly independent of concentration of droplets in the cloud. The cellular structure of the cloud as revealed by PPI and RHI photographs confirms the idea of existence of Benard Cells drawn earlier on the basis of laboratory experiments and aeroplane flights.

On super-refraction after the passage of a thunderstorm

A situation is described when the 3.2 cm high power radar at Safdarjung showed unusual ground coverage due to super-refraction near the earth’s surface. It occurred after the passage of a frontal thunderstorm. Super-refraction is generally associated with stability in the atmosphere. A case is discussed in which super-refraction occurred in an atmosphere which sustained thunderstorm activity.

Standardization of Strong Electromagnetic Fields

THE possible harmful biological effects of high-intensity electromagnetic radiation have become of practical importance in recent years with the development of high-power radar and communication transmitters1. As a result, several instruments have been designed to measure total flux density in the frequency band 30 Mc./s.−30 Gc./s. (wave-lengths, 10 m.−1 cm.). In general, these devices indicate relative values only, and suitable techniques are therefore required by means of which they can be calibrated. Some comments on this problem are given in this communication.

Evacuated Waveguide Filter for Suppressing Spurious Transmission from High-Power S-Band Radar (Correction)

H. A. Wheeler and H. L. Bachman, authors of Evacuated Waveguide Filter for Suppressing Spurious Transmission from High-Power S-Band Radar, which appeared on pages 154-162 of the January, 1959 issue of these Transactions, have submitted the following correction.

‘Ring Angels’ over South-East England

IN the course of observations on radar ‘angels’ which we have been making during the past two years, we have occasionally noted formations of angels which are clearly related to the ring angels reported by Elder1 at Ypsilanti (U.S.A.) in 1957. Fig. 1 shows a typical and fully developed ring angel which was observed on February 17, 1959. This record was obtained with a high-power L-band radar of conventional design; the signals were displayed on an ordinary plan position indicator with video map superimposed on the radar signals. The antenna was rotated at four revolutions per minute and the displays were photographed on each scan. If a film secured in this way is exhibited through an ordinary cine projector running at sixteen frames per second, an acceleration of 240 times is obtained, and in these circumstances the dynamic growth of the ring angel can be clearly observed. The ring angel commences as a strong point echo; it then extends into an annular ring, to be followed by other rings at approximately equal intervals of time. The whole phenomenon has precisely the same appearance as the ripples on a pond expanding from a point of disturbance. In the case of the rings shown on Fig. 1, eighteen rings were emitted from the centre with an average periodicity of 2½ min. and a maximum diameter of 20 miles was achieved.