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Meteor rate data tabulated from controlled parameter radar survey of Southern Hemisphere activity, noting diurnal and annual variations

Long-range, fast-fade radar echoes at 14 Mc/s observed looking north from Ithaca, N.Y., are described. They are explained in terms of backscatter from field-aligned irregularities located in a region where straight ray paths come within 10° of perpendicularity to the earth's magnetic field. A typical echo was spread in range from about 1000 to 2000 km, had a fading rate comparable to auroral fading at the same frequency, and seemed to correlate on an hour-by-hour basis with the occurrence of spread F. The minimum echo range was observed to be dependent on the penetration frequency of the F layer. This would not be predicted by geometry with straight ray paths, whereas bending of the ray paths into strict perpendicularity as a result of refractive effects does account for the observed echoes.

A ‘layered’ exponential model for the vertical distribution of refractivity in the form N = N6 exp [−c4 (z −z4)] is investigated. Here N6 and z4 are the refractivity and height, respectively, at a mandatory pressure level. The parameter c4 is the ‘best fit’ when N = N6+1 is the value at the next level where z = Z6+1. A formula for c4 is derived and is found to give good agreement, layer by layer, with the above model. This model appears to have particular merits for the case of air-to-air radar tracking.

Geomagnetic equatorial ionospheric ion temperature, comparing incoherent scatter radar and OGO-D retarding potential analyzer values

The general theory of side-looking synthetic aperture radar systems is developed. A simple circuit-theory model is developed; the geometry of the system determines the nature of the prefilter and the receiver (or processor) is the postfilter. The complex distributed reflectivity density appears as the input, and receiver noise is first considered as the interference which limits performance. Analysis and optimization are carried out for three performance criteria (resolution, signal-to-noise ratio, and least squares estimation of the target field). The optimum synthetic aperture length is derived in terms of the noise level and average transmitted power. Range-Doppler ambiguity limitations and optical processing are discussed briefly. The synthetic aperture concept for rotating target fields is described. It is observed that, for a physical aperture, a side-looking radar, and a rotating target field, the azimuth resolution is ?/? where ? is the change in aspect angle over which the target field is viewed, The effects of phase errors on azimuth resolution are derived in terms of the power density spectrum of the derivative of the phase errors and the performance in the absence of phase errors.

The problem of electromagnetic back‐scattering or radar response from cylindrical wires has been investigated using a variational method. The relation between this method and the induced emf method is discussed. To demonstrate the flexibility of the variational calculation different trial functions have been used to determine the numerical values of the back‐scattering cross section for the case of broadside incidence. The boundary condition regarding the currents at the ends of the wire is also carefully examined.

It is shown that the q type of equatorial Es at Huancayo disappears during the daytime hours when the drifts measured by Doppler shift of VHF radar echoes indicate extremely small values or an eastward E-region or downward F-region drifts. The Es-q is suggested to be due to cross field irregularities and its disappearance is due to temporary reversal of the horizontal E-region electrostatic field causing reversal or the stoppage of equatorial electrojet currents.

Millimeter wavelength radars are used to study plasma effects associated with ionized flow fields of projectiles launched at hypersonic speeds into a free-flight ballistic range. Two CW Doppler radars, at frequencies of 35 and 70 Gc/s, measure the nose-on backscattering radar cross sections during flight. The design and performance of the two radars are described in detail. A signal simulator provides absolute calibration. The purpose is to measure changes that occur in the radar cross sections of hypersonic projectiles caused by highly ionized flow fields. Under certain conditions the nose-on backscattering radar cross section of a blunt-nosed metal projectile decreases drastically when a thin, shock-produced layer of ionized gas covers the projectile. A theoretical analysis of this effect is given. Comparisons between theoretical predictions and experimental data show good correlation.

A coherent radar was used to measure the ‘sea clutter’ or backscattering of X-band electromagnetic energy from the sea surface. More than 200 recorded samples of clutter were analyzed to give power spectra of the clutter. Each spectrum was displayed as a function of frequency and of position on the water surface and was also averaged to give the mean spectrum of patches 3750 feet long. Five of the samples showed an anomalous downwind displacement of the clutter by as much as 7 knots. The displays indicate again, as in earlier Control Systems Laboratory measurements, that the upwind edge of the clutter spectrum is smooth for all wind speeds observed, but that the downwind edge, for sea state 3 or above, is broadened in an irregular fashion as a function of range. This irregular broadening implies a considerable variability, from patch to patch, in the downwind side of the probability distribution of velocity of scatterers on the sea surface. The width at half-power of a mean spectrum is proportional, for reasonable assumptions, to the width at half-maximum of the probability distribution of scatterer velocities. The variation of the latter width, Δ0, with sea state can be represented by the equation (expressed in consistent units) Δ0=11H1/3/Tm where the numerical factor is dimensionless, H1/3 is the significant wave height, and Tm is the period corresponding to the maximum of the energy spectrum for the water waves themselves when this spectrum is plotted as a function of frequency. This equation fits the experimental data within about 10 per cent for bandwidths in the range of 2 to 5 knots (64 to 160 cps) and wind speeds in the range of 8 to 19 knots. The bandwidth of the clutter is found to be approximately proportional to the wind speed. The relationships of clutter bandwidths to wave and whitecap velocities, radar depression angle, and wind direction are also discussed.

A series of cesium-seeded explosive bursts in the 90- to 110-km altitude region have been observed with meter and decameter wave radar. Detailed measurements of contact surface expansion, undulation, and stabilization have been used to acquire estimates of the altitude dependence of atmospheric pressure and density in the lower ionosphere. It has been found that events in the development of the contact surface are retarded relative to those predicted by Brode’s blast wave model, and this retardation is interpreted as evidence of magnetohydrodynamic effects upon the blast wave. Comparison of the results of these observations with previous results of Rosenberg (1964, 1965) suggests that a suitable combination of optical and radio-frequency instrumentation can be utilized to study in detail both the neutral gas and the magnetofluid characteristics of the lower ionosphere simultaneously.

Recent probes of the planet Venus reveal a probable surface temperature exceeding 700K and a pressure exceeding 100 atm. A very dusty lower atmosphere may exist which is composed of micron-sized particles kept airborne by mild turbulence and a gentle circulation of deep adiabatic currents. A study of surface conditions responsible for generation and persistence of surface dust clouds is of fundamental importance in the radiative and dynamic properties of the atmosphere. Also spurious radar echoes may be caused by suspended particulate matter, thus explaining the high relief reported by radar altimeters.

This study is essentially an extension of the work of Daily, et al. [1, 2] and Richard, et al. [3], who demonstrated that 12.3-cm radiation could produce lens opacities in the eyes of animals. Because of the broader implication of their findings in terms of human analogy, this present investigation was designed to gain some idea of what microwave power densities should be considered dangerous for human exposure. Both wavelength and power densities used for this purpose are of interest in the applied fields of microwave diathermy, radar communications, and microwave research.

The object of this research is to investigate the feasibility of adapting the conventional pulsed radar technique for closerange back-scattering measurements for obstacles of arbitrary shape and small scattering cross sections. The time-separation or microwave-pulse method described in this paper differs essentially from all previously used laboratory methods in that the scattered field does not mix with the incident field at the detector and is separated from it in time. The essential experimental arrangement of this method is similar to that of the CW magic-T method except that a source generating very short pulses is used instead of CW. Preliminary experimental data for thin circular metallic disks show that the pulse method is a feasible one, since the measured results are in close agreement with the theoretical values. Accurate back-scattering measurements for obstacles of arbitrary shape and small scattering cross sections should be obtainable by this method provided a short microwave pulse of high power level is available.

It is proposed that the range derivative of the logarithm of the ratio of average echo powers from two (S- and X-band) synchronized and slaved radars would yield a highly reliable indication of the boundaries of hail shafts. In the presence of rain alone, and ignoring fluctuations, this derivative would always be positive and proportional to the incremental difference in attenuation at the smaller wavelength. In general, the derivative has the same sign as the hail concentration gradient and attains negative values on the far side of a hail shaft. Without hail, signal fluctuations are the only possible source of negative derivatives, and so of false alarms. Thus, a small negative threshold level would avoid the identification of the effect of signal fluctuations at the far side of a hail shaft; similarly a large positive threshold would avoid identifying regions of intense rain as the near side of a hail shaft. This approach is capable of detecting smaller concentrations of hail with greater conf...

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

The rapid variabilty of pulsar signals and the dispersive nature of the interstellar medium introduce a number of problems which are not inherent in other radio-astronomical observations. These problems are discussed and some of the techniques currently being used to cope with them are described.

The scattering of electromagnetic waves by clouds of small spheroidal obstacles is considered from a theoretical standpoint. Numerical data are obtained for the case of clouds composed of partly melted ice particles. These results are applied to the interpretation of ``bright band'' radar echoes from meteorological formations.It is also shown that these echoes may contain a component with polarization at right angles to that of the transmitted beam. It is suggested that this property could be utilized in certain cases to provide additional information as to the nature of the scattering particles.

By assuming that auroral radio reflections are produced by volume scattering in clouds of ionization having the same spatial configuration as the visible auroral structures, and by taking into account the radar pulse duration and antenna beam width, it is possible to predict the probability of echo occurrence as a function of range and azimuth. This echo distribution is quite similar to that observed experimentally even when "aspect sensitivity" of the individual scatterer is neglected. Unfortunately, the optical evidence is not sufficiently extensive to permit precise calculations to be made, nor the radio evidence to permit detailed comparisons, but previous estimates of the shape of the scattering structures that have been based on the azimuthal echo distribution without regard to the factors discussed here are likely to be seriously in error.

A frequency-modulation radar technique especially suited to measurement of atmospheric attenuation at millimeter wavelengths is described. This two-way transmission method employs a single klystron, a single antenna and a set of spaced corner reflectors whose relative reflecting properties are known. Since the method does not depend on measurements of absolute antenna gains and power levels, absorption data can be obtained more readily and with greater accuracy than by the usual one-way transmission methods. Application of the method is demonstrated by measurements in the 5-mm to 6-mm wave band. The results have made it possible to assign an accurate value for the line-breadth constant of oxygen at atmospheric pressure; the constant appropriate to the measurements lies between 600 and 800 MCS per atmosphere.

The effect of ion-neutral atom (or molecule) collisions on the excitation of ion-acoustic instabilities in the auroral ionosphere is considered. These collisions may play an important role in selecting the wavelength of the perturbations that are most likely to grow at any given height. The results of the calculations are compared with observational evidence obtained from radio star scintillations and radar aurora echoes.

Doubly scattered radiation magnitude as function of heights and aerosol concentrations for bistatic laser radar

A type of analog integrating moving window detector for use with a scanning pulse radar is examined. A performance analysis is carried out, which takes into account both the radiation pattern of the antenna and the dynamic character of the detection process due to the angular scanning of the antenna. An expression for the false alarm rate of the detector is first derived and evaluated numerically. The detection performance and angular accuracy are next determined in a direct Monte Carlo simulation of the detector on a digital computer for both no fading and pulse-to-pulse Rayleigh fading. Finally the influence on detection performance of the width used for the moving window is investigated.

Some general sequential estimation and sequential detection processes are provided with an analytical formulation through use of the functional equation technique of dynamic programming. Some reductions which are useful from the computational viewpoint are indicated, and several applications to radar and communication system theory are sketched. (Author)

Radar ranging experiment onboard Jupiter orbiter, concerning perturbations, gravitational harmonics and short arc orbit determination

The brightness temperature of an element of a planetary disk is dependent both on the direction of linear polarization to which the observing antenna is sensitive and the inclination of the element to the line-of-sight. Instruments of high resolution can be used to measure this dependence, providing values for the dielectric constant and emissivity of the planet's surface. The behavior of theoretical models, to which observations may be compared, is given. Observations of the Moon and Venus are presented as examples of application of this theory. The dielectric constant of the Moon at 21 cm is found to be 2.1, in good agreement with the radar results. This implies the emissivity at the center of the disk is 0.97, yielding 241 ± 26°K as the actual surface temperature at the center of the disk. The radiometric data for Venus show the expected behavior but the dielectric constant obtained is inconsistent with the value obtained from radar experiments.

A common problem in waveform design is to adapt the transmitted signal to the target environment in order that the interference from extended fields of scatterers is reduced. This problem is investigated here for the special case of detection of a single target in the ``vicinity'' of an extended clutter space. The paper considers the possibility of confining the matched-filter response in delay and Doppler, or ambiguity function, to a narrow strip with arbitrary orientation in the delay-Doppler plane. It is shown that strict confinement of the response is achievable only with waveforms that are unlimited in both time and frequency domain. With practical waveforms, which are necessarily of finite extent, one merely can trade close-target separability against detectability in the background clutter. Thus, one form of the resolution problem is exchanged against the other. The paper examines these effects quantitatively.

Correlation studies of the radar echo occurrence rate from aurora in half-hourly intervals at Ottawa, S and Sd components of the horizontal magnetic field H at Agincourt, and the disturbance diurnal variation of earth current at Crow River have been carried out. Short-time variations in auroral echo strength and moderate perturbations in H have also been correlated. The auroral echo occurrence rate seems to have a diurnal variation characteristic similar to that of H. It is found that auroral activity always precedes magnetic activity. The variation of the delay time between the two phenomena shows a local time dependence, being practically constant and quite small (0–15 minutes) before local midnight and increasing afterwards. This variation of the delay time appears to have a connection with reports of others regarding reversal of the direction of auroral ionization drift from west to east somewhere around midnight with subsequent magnetic perturbations which change from positive to negative.No definite conclusion could be reached regarding the relationship of earth current to other factors because of a practically random variation of cross-correlation coefficients from month to month.

An X-band pulsed-Doppler radar having its beam fixed at an elevation angle of 3°, has supplied new data on radial velocity spectra in two showers. It was found that the mean Doppler velocity, variance of the Doppler spectrum, and radar reflectivity varied markedly over distances of less than a kilometer. The observed variances were less than about 1 m2 sec−2 in more than 80% of the observations and exceeded 3 m2 sec−2 in about 4% of the cases. An analysis of ΔV/Δr, the radial gradient of the mean Doppler velocity, yielded a nearly Gaussian curve having a mean of 0.2 × 10−2 sec−1 and a standard deviation of 5.8 × 10−3 sec−1. The effects of the radial gradient of the radial wind apparently can explain less than about 15% of the observed variance of the Doppler spectrum. It appears that a major part of the variance is attributable to scales of motion smaller than the dimensions of the sampling volume.

Radar waves propagating through the turbulent troposphere acquire phase fluctuations which appear as aperture phase errors in synthetic-aperture radar systems. The phase error description follows directly from Tatarski's theory of wave propagation through turbulence; for most situations of interest, the phase error is Gaussian with stationary first increments. The structure function of the phase error is a function of the radar parameters and of the vertical profile Cnm(h) of the microwave refractive index structure constant of the turbulence. A closed form expression for best attainable resolution can then be given as a function of these same parameters, via the results of a phase error analysis by Brown and Riordan. Published data on Cnm(h) and its optical-region counterpart are reviewed. The data from a recent microwave propagation experiment by Thompson and Janes are then analyzed and are consistent with the order-of-magnitude estimates of Cnm: Some unsolved problems associated with applying the results to synthetic-aperture systems are discussed.

A theory is presented to describe the statistical aspects of tracking a complex isolated structure, such as an aircraft or naval vessel, by radar. The results are expressible in simplest form when the target subtends an angle small compared with the beamwidth. Other situations require special consideration and treatment, but can be attacked by the same general methods. However, when the angle subtended by the target is small, a single description applies to all radar tracking systems. An apparent and an effective radar center are defined and their statistical properties derived. Special treatment is given to additional noise arising in conical scanning due to amplitude fluctuations as such. The theory provides information relating to the spectra as well as to the probability densities and rms values of the pertinent quantities. It must be understood that the theory is approximate, is based on a particular model of the target, and leaves the determination of certain critical parameters to experiment in the case of any particular target.

This demonstration-experiment was developed as part of a one-semester course for upperclass nonscience students. Materials are offered which allow student data taking and analysis of radar moon echoes.

Based on precalculated data for the position and velocity vector of the injection points for the Explorers I through V, orbital elements are derived and compared with the actual orbital elements at injection time, calculated from position and velocity data obtained from radar measurements. Calculations are also made for the different orbital periods of a satellite perturbed by the Earth's oblateness. For Explorer I, it is shown that the actual orbital elements derived from tracking observations agree well with the actual elements derived from early astronomical observations.

The technique of measuring ionosphere motion from the shift in the incoherent-scatter ion line has been known for some time. The underlying assumption in the adaptations of the technique applied so far is that there are no detectable current-induced asymmetries in the spectrum. In the auroral zone this assumption can be violated during magnetospheric storms. To cope with this possibility we use an estimate of the first moment of the spectrum together with a matched-filter-like estimate. The first moment is the sum of the first moment of the unshifted spectrum plus the Doppler shift. The matched-filter estimate, while not unaffected by asymmetries, tends to give an estimate closer to the Doppler shift. Hence, a difference between the two estimates is an indication of a current flowing in the range gate where the spectrum is measured. We assume that no other sources of asymmetry are present, although a large temperature gradient would have a similar effect. In principle the difference can be calibrated to give the magnitude of the current. This step is not yet completed owing to uncertainties in the composition of the ionosphere at low altitudes and a loss of frequency resolution due to the finite pulse length. The detectability of the currents by our method, however, is not affected by poor frequency resolution. Preliminary results from the Chatanika Auroral-Zone Incoherent-Scatter Radar are presented which show large velocities correlated in detail with simultaneous magnetometer data. Also an indication of a current flow has been observed in premidnight data taken on a very active night. An azimuth scan showed the sense of the current to be predominantly westward.

From 54 radio aurorae recorded at Kuhlungsborn ( Φ = 54°) since 1958 by a 33 Mc/s radar with rotating antenna some results are reported concerning the echo geometry, the remarkably small variations in height of the echoing region, the diurnal seasonal and sunspot cycle variations of auroral echo activity and the correlation with geomagnetic activity, being systematically dependent on season.

A backscatter, pulse-type, patrol radar has recorded meteor echoes continuously near Ottawa for the years 1958 to 1962 inclusive. Five-year mean hourly echo rates for each day in the year are presented for all echoes counted, a total of some seven million, and for echoes of duration greater than or equal to 8 seconds. The diurnal vaiations in hourly echo rates throughout the year are given as five-year means in five-day groups. (Author)

This paper presents a computational method for the calculation of probability of detection using measured radar target cross-section data. The described method can also be used for probability of detection calculations when the radar target cross section follows a specified probability density function. Using the computational procedure of the paper, a number of curves are generated which can be used for probability of detection calculations with exponential and Gaussian radar target cross-section distributions. The results obtained using theoretical distributions are compared with the corresponding results using actual target cross-section measurements. The results of computer runs are compared to the corresponding values in the literature where available.

In relating the frequency distribution of the durations of radar echoes from meteor trails to the mass distribution of the meteoroid flux, two major effects must be taken into account. Because bright meteors tend to be observable by radar from any angle, the rate of long-duration echoes is enhanced relative to short-duration echoes. This effect is particularly pronounced for the Ottawa radar which has wide-beam antennas. On the other hand, the effect of electron attachment is to suppress the long-duration echo count, particularly for low-velocity meteors, which produce ionized trails at lower altitudes.The influence of both these effects on the observational results from the Ottawa meteor radar is examined quantitatively.

Measurements of the velocity of propagation of pulses of radio waves through the atmosphere using techniques developed for accurate radio aids to navigation are described. The time of travel of pulses between two ground stations is accurately determined in terms of calibration marks generated by an accurate crystal, account being taken of the measured delays in the receiving equipment. The mean value obtained for the velocity of propagation in the atmosphere at ground level is 299 695 ± 50 km/sec. This value does not differ significantly from that calculated from the best optical values for the velocity of light in free space by allowing for the refractive index of the atmosphere.

The mechanization of a gimballess inertial system for space navigation is considered. An error analysis reveals that the errors contain both sinusoidal and diverging components. Error damping methods are proposed and it is shown that damping can be achieved by using appropriate damping circuits and auxiliary information obtained from devices such as stellar trackers, velocity-measuring optical Doppler, or radar Doppler. Computer-stored reference-trajectory information can also be used for error damping.

This paper discusses the design and construction of a branch-fed, variable-phase, 20 to 55 Mc array of 48 log-periodic elements. Phasing to control-beam direction is described and the correction necessary for ionospheric refraction is presented in terms of vertical incidence critical frequency. The array gain as measured by moon-bounce techniques is found to be in good agreement with the theoretical value.

The purpose of this paper is to summarize some of the results of lunar studies carried out in the Radiation Laboratory of The University of Michigan during the past 3 years. Apart from an associated program which is the subject of a later paper [1] by Fensleret al., these studies have been confined mainly to an analysis of radar scattering and thermal emission data, but in the course of this work, values have been obtained for some of the physical constants of the lunar surface.

Results of wind-tunnel tests of wind-induced vibrations in circular aluminum tubular members of large radar antenna space frames; curve for von Karman lift coefficient and semi-empirical means for evaluating effect of self-amplification of vibrations is presented; system of aerodynamic spoilers and their application. (22 refs.)

Data obtained in a thunderstorm with a vertically pointing Doppler radar are analyzed to find the size distribution of raindrops at heights below the 0C level. Drop-size distributions were computed using the updraft UR deduced by Rogers' method and two other updrafts, namely, UR − 1 and UR + 1 m sec−1. It is found that the drop-size data at all the heights may be well represented by the exponential equation, N (D) = N0 exp(− ΛD), in which N (D)ΔD is the concentration of drops in the diameter range D to D + ΔD, N0 = 0.07 R0.37 [cm−4], and Λ = 38R−0.14 [cm−1], R being the rainfall rate (mm hr−1). For R ≳ 3 mm hr−1, the distribution is steeper and N0 is greater as compared to the Marshall-Palmer distribution. For radar reflectivity factors Z in the range 1–105 mm6 m−3, the relationship between the mean Doppler velocity and Z for the distribution agrees with that given by Rogers to within 1 m sec−1. The following equations have been found between the water content M, median volume diameter D0, radar ...

In this paper a grid separation cavity for CW oscillator operating in L-band (1000–2000 Mc/s.) using pencil tube developed to be used as a Local Oscillator in S-band Pulsed Radar Transponder, devel...

This paper deals with airborne Doppler velocity measuring systems. In particular, it deals with the character and limitations of the velocity data provided by such systems. The Doppler effect is discussed and quantitative expressions for the frequency shift are derived. The relationship between the Doppler shift and aircraft velocity is such as to show that the fundamental capability of a Doppler system is the measurement, in the coordinate system of the aircraft, of one component of aircraft velocity for each beam of radiation employed. Certain effects of beam geometry on the measured velocity components are demonstrated quantitatively. The earth's surface as a medium for producing a radar return signal can be regarded as being constituted of a multitude of randomly situated scattering centers. The consequences of this as it bears on the nature and properties of the return signal are discussed. It is shown that the signal is noiselike and has a spectrum which is centered at a Doppler shifted frequency and which has an appreciable bandwidth. Outlines of theoretical methods for calculating the signal spectrum from a knowledge of antenna directional characteristics and other system and operational parameters are presented. It is shown that the frequency of the Doppler signal cannot be measured without error in a finite time.

Observations of Doppler spectra from particles 610 m above the ground were obtained by means of a vertically pointing X-band radar during a period when large hail was falling at the ground. It was found that the variance of the Doppler spectrum was a fairly good indicator of maximum hailstone sizes. Calculations of ice-particle size spectra were made on the basis of assumptions of particle shape, composition and fallspeed. The many assumptions needed to bring calculated ice-sphere spectra into approximate conformity with observations indicates the complexity of this procedure and the need for at least another independent observation of a property of the hailstones. Measurements of depolarization might yield an independent estimate of particle shape. It is concluded that the pronounced minima in the backscattering curves of large ice spheres should serve as an independent indicator of the speed of vertical air motions.