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An instrument that has been developed for measuring the deformations in shape that result from the movement of a radio telescope reflector is described. A radar technique is used to measure distances from near the focal point of the reflector to selected points on the reflector surface. The short term accuracy of the instrument is ±0.003 in) and when used on the 140-ft telescope in Green Bank, W.Va., good agreement was found between calculated and measured deformations.

We compute the linear parametric convective amplification of electron plasma waves by an O mode pump propagating vertically into a vertically stratified ionosphere. The upshifted plasma line compares favorably with Arecibo observations, center frequency, spectral width, and possibly amplitude when the radar is aimed in a northerly direction. The dependence of the computed enhanced plasma line shape upon density scale length, electron-to-ion temperature ratio, pump power, density gradient scale length, and backscatter radar incidence angle is investigated.

Low frequency radar scattering data is used for the identification of aircraft. It is shown that such radar data lies on two-dimensional surfaces in n -space. A bilinear approximation for these surfaces is described. Surface intersections using this approximation can be found simply and directly without solving a system of n simultaneous nonlinear equations. This intersection information can be used to show separability and effect feature reduction. The approximation is utilized to construct a modified nearest neighbor algorithm, which is evaluated by computer simulation experiments. These experiments showed a phenomenon of “bias”, where one aircraft data surface is more susceptible to misclassification in the presence of noise than the surface corresponding to another aircraft. This “bias” observed is shown to be related to the surface characteristics of the data surfaces involved, specifically proximity and relative curvature of corresponding points on the two surfaces.

The entire earth-facing lunar surface has been mapped at a resolution of 2 km using the 3.8-cm radar of Haystack Observatory. The observations yield the distribution of relative radar backscattering efficiency with an accuracy of about 10% for both the polarized (primarily quasispecular or coherent) and depolarized (diffuse or incoherent) scattered components. The results show a variety of discrete radar features, many of which are correlated with craters or other features of optical photographs. Particular interest, however, attaches to those features with substantially different radio and optical contrasts. An anomaly near 63° is noted in the mean angular scattering law obtained from a summary of the radar data.

HF radio waves backscattered from the ocean surface can be used to measure ocean surface currents. Measurements of the range-Doppler spectrum of these signals yield the wavenumber k and the frequency ω of an ocean surface wave and its phase velocityν = ω/κ relative to the radar. Subtraction of the phase velocity of the wave in still water, c = √(g/k), yields a measure of the average current from the surface to a depth of the order of (2k)−1. A measure of the current shear is obtained by observing at more than one radio frequency. To test these ideas, surface currents were measured using both a conventional and the HF technique, and reasonable agreement was found.

A 32-element HF-phased array has been used to study the angular spectrum of spread F returns from an ionosphere modified by the powerful radio frequency heater transmitter at Platteville, Colorado. The diagnostic radar is a coherent pulse system that provides an angular resolution of 2.7° at the midband frequency of 7.5 MHz, a range resolution of 30 km, and a Doppler resolution of 0.08 Hz. The results are presented in the form of sky maps (brightness versus azimuth and elevation) of the returns as a function of group delay, Doppler shift, polarization, and sounding frequency. The principal result is that the returns that suffer the greatest group delay at a given sounding frequency come from a direction looking up the earth's magnetic field and exhibit negative Doppler shift. Ray-tracing simulation of the observed dependence of the range and the Doppler on the angle of arrival of the returns supports the view that the heater-generated spread F is caused by field-aligned ducts produced within the heated volume. A simulation run for Arecibo, Puerto Rico, in comparison with that for Platteville, reveals that the group delay spread is about the same and the angular spread is approximately in the same ratio as the heater beam widths at the two locations.

An improved technique for obtaining stereo radar image pairs is described. The technique uses a unique combination of two different radar beam pattern characteristics. The resulting stereo radar images are illuminated from very nearly the same aircraft position which results in radar shadow and backscatter characteristics which are very similar and in improved image registration possibilities. The reduction in illumination angle and aircraft position differences is shown to be nearly an order of magnitude or more when compared with a previously proposed single flight technique which used two vertical fan beam patterns at different azimuth angles. As a related sidelight it is shown that this previous technique requlres the two fan beam patterns to generate parallax on the images and thus can not be implemented with synthetic arrays squinted at two different squint angles.

The theory of linear statistical models is implemented to obtain an algorithm which accurately locates radar sites. True bearing and navigation data are used as input. The linear model developed is adaptable and allows removal of bearing errors that are nonrandom, or systematic. The model may be written in recursive form and used for real-time applications.

The evolution and state of development of the radars used in the Ground-Controlled Approach (GCA) systems of the U.S. Air Force is described. Emphasis is placed on the radar requirements of this application and the evolution made possible by the advances in component technology. We first review the concept of GCA operation and show how this leads to the requirements of the two radars in the system. Next we discuss the early history of GCA and the AN/MPN-1, the first operational system. The evolution of the GCA radars since the AN/MPN-1 is then summarized. Finally, we describe in more detail the AN/TPN-19. This is the most recent GCA system to be developed, and it makes effective use of array technology, frequency diversity, monopulse, pulse compression, and computer control.

This paper surveys the field of automotive radar and represents an expansion of a previous paper, "Automotive Radar-Problems and Promises" [1]. Both the roadside environment in which the car and driver operate and on-board physical environments in which the electronics must function are treated. Applications involving speed sensing, predictive crash sensing, obstacle detection, braking, and station keeping are addressed. Current radar system state of the art is reviewed. Considerations relating to target discrimination, weather penetration, and basic radar system parameters are covered. Modulation techniques for range determination are examined, and radar system configurations are discussed in an effort to identify the advantages and disadvantages of each. It is concluded that although considerable development work remains before radar becomes a practical automotive system, significant progress has been made.

High angular resolution is a desirable property of mapping and reconnaissance radar systems. The synthetic-aperture principle reduced the beamwidth of airborne radar by as much as two orders of magnitude. Notwithstanding the long interest in the subject, a quantitative relationship is lacking between beamwidth and resolution. This paper is an attempt to overcome this deficiency. Among its several results, it is shown that the angular resolution of synthetic-aperture radar can be considerably poorer than expected. It is also shown that a modest tapering of the synthetic aperture in those cases offers significant improvement.

Phased-array radar systems using wide-band linear-FM pulses suffer from array dispersion. This causes a loss in signal-to-noise (S/N) ratio and in radar range resolution (a broadening of the compressed-pulse width). Depending on the choice of the receiver matched filter (MF) and weighting filter (WF) one or the other of these effects may be minimized. The effects of dispersion in a square planar array with either a parallel feed or a center-fed series feed are studied. Loss in S/N ratio and in range resolution are determined for typical cases, and general curves are given for arrays with arbitrary size, scan range, and signal bandwidth. It is shown that there is an optimum or maximum-useful signal bandwidth for each array, for which the minimum S/N-loss MF-WF design is the same as the ideal-compressed-pulse-shape MF-WF design. For pulses having greater signal bandwidths, time delay steering should be used in the array.

This paper studies the application of Kalman filtering to single-target track systems in airborne radar. An angle channel Kalman filter is configured which incorporates measures of range, range rate, and on-board dynamics. Theoretical performance results are given and a discussion of methods for reducing the complexity of the Kalman gain computation is presented. A suboptimal antenna controller which operates on the outputs of the angle Kalman filter is also described. In addition, methodological improvements are shown to exist in the design of range and range-rate trackers using the Kalman filter configuration.

Boundary layer probing by multiple remote sensors can greatly improve the understanding of processes in this complex region. For this purpose one needs to know the unique information each individual sensor can provide. Two promising boundary layer remote sensors, a microwave, frequency-modulated, continuous-wave (FM-CW) radar and a laser radar (lidar), were operated simultaneously to probe a common volume. As expected, the lidar sometimes separately detected aerosol layers, notably cloud bases, and the radar sometimes separately detected refractive layers and insects. Boundaries of aerosol structures were often found to be regions of radar returns such as in layers, convective activity, and breaking waves. In contrast, however, a refractive layer was observed within an apparently well-mixed aerosol layer. The data indicate that the radar may have a characteristic echo which is coincident with cloud and fog tops. This experiment shows that FM-CW radars and lidars can separately sense layering in t...

Radio scattering measurements have been made of a region of the ionosphere above the Institute for Telecommunication Sciences' ionospheric heating facility at Platteville, Colorado. Strong scattering was observed at frequencies in the HF and VHF bands. The scattering has been shown to originate from electron density fluctuations that are highly elongated in the direction of the geomagnetic field. Radar scattering cross sections of 70 to 80 dbsm are measured in the HF and low VHF bands. The scattering cross section decreases at a rate of 20 to 30 db per octave at the high end of the VHF band. The scattering irregularities are produced by operation of the heating facility with o-mode polarization at frequencies that reflect within the ionosphere. The strength of the scattered energy decreases at a rate of at least 10 db per degree for observation geometries that do not match the geometry for specular reflections from long cylinders aligned with the geomagnetic field. The spatial distribution of irregularities has been estimated for both E- and F-region heating. The temporal properties of the scattering have also been determined including the frequency spectrum of the scattered signals. The processes by which ionospheric heating produces these irregularities are not yet fully explained. Several potentially useful applications of radio scattering from such irregularities are discussed.

The paper presents a model for radio wave scattering from the ionospheric irregularities generated by the intense radio wave transmissions from the Platteville heater. The model is based upon the HF-UHF radar backscatter observations for a physical description of the scattering medium and upon the theory of weak scattering (Born approximation) from anisotropic irregularities for mathematical development. According to the model, the electron density fluctuations responsible for radio wave scattering having an rms value of 1 to 1.5% are aligned along the earth's magnetic field and are distributed in a diffuse pancake-shaped volume of 15 km gaussian thickness vertically and of the size of the heater beam which is 100 km in gaussian diameter horizontally. At radio frequencies the irregularities within the disturbed volume are highly aspect sensitive and consequently only those scatterers which lie on the surface of specularity where a radar views transverse to the magnetic field count in contributing to the received signal. Model computations have been made of the scattering cross sections for monostatic as well as bistatic radar configurations and they are found to be in good agreement with the observations. The radar cross section at a given frequency for bistatic geometry is substantially greater than that for monostatic geometry, all else being equal. Finally, it is shown that the width of the scatter-illuminated bands on the ground is set primarily by the finite dimensions of the scattering volume rather than by the finite aspect sensitivity of the individual scatterers.

a unique aspect of the San Francisco Experimental Vessel Traffic System has been its extensive use of real time automatic processing technology. Automatic detection and tracking of vessels in radar coverage areas has successfully been accomplished even in the presence of clutter. Vessel movement information has been extracted, presented to operators on computer-animated displays, and traffic analyzed both automatically and at the request of operators. But these demonstrated capabilities should be employed only as a guide to the design of future systems and not interpreted as a literal prototype configuration. Future system designs should assume traffic will be controlled, rather than advised. Risk analysis based upon port geometry, traffic levels, and minimum turning radius can contribute to assessing deployment priorities. Vessel routing should be constrained to follow narrow tracks rather than broad lanes. A minimum configuration would be based upon a computerized Vessel Movement Reporting (VMR) system. Data entry and retrieval terminals could be available within the maritime community. Information, including guidance, could be selectively distributed to active ships via a novel multiplexed television transmission. All radar configurations would include automatic detection and tracking equipment. Finally, area navigation systems could be integrated with VTS. The opinions expressed in this document are those of the author, presented in the interest of stimulating discussion, and they do not necessarily reflect the views of either the Applied Physics Laboratory or the United States Coast Guard.

Rocket borne Langmuir probe measurements of electron temperature in the E-region are examined in relation to recent laboratory investigations of surface drift effects which can lead to erroneously high and time-dependent electron temperature measurements. The rocket data is consistent with the laboratory expectations thus supporting the suggested importance of surface effects in rocket measurements and in relation to the E-region discrepancy with simultaneous incoherent radar scatter measurements.

Total electron contents obtained by the differential Faraday method during 26 near-overhead passes of the Beacon-B satellite at Aberystwyth are compared with the results of integrating vertical N(h) profiles observed simultaneously by the incoherent scatter radar at Malvern, 117 km to the east. In 19 cases agreement within the experimental errors was found with a standard method of analysis of the satellite data, using a constant value of the magnetic field function M ; in three cases agreement could be reached only by allowing for an unsuspected ambiguity of π radians in the measured differential rotation angle; in two cases when the F2-peak was abnormally high it was necessary to adjust M ; in one case the presence of strong waves made the comparison invalid, and in one case there was a significant unexplained discrepancy. Computation of the mean Faraday height, hF, for the 26 incoherent scatter profiles showed that hF is roughly proportional to the F2 peak height, hmax, and that (hF—hmax) has a mean value of about 80 km. There is some indication that the use of the normal first order expression for the total Faraday rotation leads to overestimation of electron content: this problem can be dealt with by an empirical modification of the standard analysis.

Radar echoes from Venus have been mapped at a wavelength of 3.8 cm from approximately 270 deg to 10 deg in longitude and -50 deg to +50 deg in latitude during the inferior conjunctions of 1969 and 1972. Observations made in April 1969 and again in June 1972 both show the same regions of high reflectivity as well as several large regions of low reflectivity.

In radars that achieve a high subclutter visibility by coherent processing over several pulses, a serious problem appears in the form of blind Dopplers, or "speeds," at which target detection is impossible. Of the possible methods of eliminating these blind speeds, the most basic one that is employed when the performance requirements are high involves the use of several PRF's. These PRF's are chosen so that coverage is obtained at any Doppler with at least one PRF. The problem faced by the radar designer is to select the set of PRF's and the pulse numbers for each PRF so that the search frame time is minimized. This paper evolves a systematic method for the design of the blind-speed elimination scheme. A formalized approach is offered that shows the possible combinations of wavelength, PRF, and pulse number and the tradeoffs involved, without introducing the confusion ordinarily associated with multiparameter choices.

The developmental activities pertaining to the RF RATIOMETER was necessitated by the need for the continuous monitoring of VSWR in MEDIUM RANGE TRACKING RADAR being developed at Thumba Equatorial Rocket Launching Station, Trivandrum, and give warning when the VSWR reaches a value at which arcing is likely to occur. Since it is not possible to use the slotted line techniques at such a high power level as 1 MW, RF RATIOMETER becomes imperative.This equipment is coupled to the Tracking Radar in such a way as to trip it off when the VSWR exceeds a safe value. This equipment has the capability of measuring the VSWR over the complete frequency band of 10 MHz to 10 GHz.

The National Maritime Research Center, Kings Point, N.Y., is conducting projects dealing with the “new technology” in the field of navigation. This paper consists of a survey of this area of activity of the Center. The intent is not only to disseminate information to the wide community of navigators but also to structure a mutually beneficial communications link between the NMRC and the Institute of Navigation. The paper will cover the following projects, some innovative, others extensions of previous programs: —RAPS (Radar Automatic Plotting System) —MASS (MarAd Anti-Stranding Sonar) —TRANSIM (Simplified Transit) —MARINE RADAR TRANSPONDER —MARSCAN (Maritime Satellites Communication and Navigation System) —INTEGRATED CONNING SYSTEM

This paper discusses the scattering of waves by an irregular boundary. Classical single scattering theory and Kirchoff diffraction theory cannot handle waves at near-grazing angles of incidence nor account satisfactorily for the intensity of the field scattered into near-grazing directions. Problems of this type are of increasing scientific and technological importance in such fields as radio astronomy, terrestrial radio communication, the design of radar and sonar devices, as well as in many geophysical situations involving large-scale wave motions. In this paper a theory of multiple surface scattering is proposed, and described, in terms of a simple model problem of the scattering of sound from a randomly irregular, hard surface. Multiple scattering becomes significant at grazing directions of incidence and scattering, and the theory is expected to give an accurate description of the scattering processes in such circumstances. The analysis is strictly valid only in the case of small surface roughness, and in this limit numerical results are presented which illustrate the considerable divergence between predictions based on the multiple scattering theory and those of single scattering and Kirchoff diffraction theory.

The problems of low-angle tracking over the earth's surface are explored in the light of rough-surface scattering theory. A detailed model of diffuse scattering is constructed which agrees with available test data and which permits the power distributions in radar coordinates to be estimated. Using this model, the potential performance of various techniques proposed for avoidance of multi-path is evaluated, Several are found effective in maintaining tracks of reasonable accuracy down to one-fourth beamwidth above the horizon, but no generally practical solution to height measurement below that angle appears available.

The use of Doppler ultrasonics provides one of the few, if not the only, methods of noninvasive measurement of blood flow and velocity in the body. In terms of overall accuracy the pulsed ultrasonic Doppler flow meter, operating in a radar-like range-gated manner, currently offers the best solution. However, under certain circumstances this device suffers from an inherent lack of spatial resolution, resulting in the distortion of the measured velocity profiles. The device is modeled as a convolution integral, incorporating the physical characteristics of the flow meter, and those of the velocity field, as established in previous work. The distortion of the measured velocity profile is corrected by solving the integral equation, or “deconvolving” using the discrete Fourier transforms implemented on a digital computer. The methods discussed for obtaining the “true” velocity profile require only a knowledge of the flow meter characteristics and its output. No assumptions as to the nature of the true profile are necessary.

Advances in the design, development, and fabrication of key microwave components along with those in electronics have resulted in growing optimism about the application of radar technology to solving the automotive highway collision problem. However, before an automotive radar system can be fully realized, a major effort will be required to define the environment in which the system must operate, and to obtain a fundamental understanding of the influence of these RF parameters. One such parameter which will have a considerable effect on the design of automobile radars is that due to the presence of natural and man-made surfaces within the beamwidth of the antenna. Generally, the presence of such a surface will result in incident RF energy being reflected off the surface in a forward direction and some portion being scattered in a backward direction. This paper presents the results of a program which was designed to measure this type of reflectivity characteristic for common road surfaces. Measured data are presented along with a theoretical study demonstrating the influence that this phenomenon can have on highway collision radar systems.

Enhancements of various features of the incoherent scatter spectrum are observed when the ionosphere is illuminated with powerful, high frequency radio waves. The radio waves excite plasma instabilities producing lines or more complex spectral features near the local plasma frequency, at the local ion acoustic frequency, near the local gyrofrequency, and near twice the gyrofrequency. The enhancements occur in a thin slab as observed by the incoherent scatter radar and at both upshifted and downshifted frequencies with respect to the probing radar frequency. The enhancements are observed to vary with time when the excitation is held constant and is turned on or off. The high power radio waves are produced by a 160 kw transmitter feeding a log-periodic pair of curtains mounted at the focus of the 1000-ft reflector and covering the frequency range from 5 to 12 MHz. The effects are observed with the incoherent scatter radar using the same reflector and with ionosondes and photometers. The frequencies of the enhanced plasma line and the ion line and their relation to the pump (high frequency radio wave) frequency are predictable from available parametric instability theory. Other spectral features are being explained as the theory develops with the help of the observations. There remain some discrepancies, in particular the asymmetries in intensity, width, and fluctuations of the upshifted compared to the downshifted plasma lines.

RF pulses are used in radar and sonar to detect and locate targets in extended media. Short RF pulses (and impulses) can be used to find buried objects or voids by echo sounding, or can be used to probe snow fields or the depths of the earth. Although similar to radar in principle, there are important differences in these applications that can lead to significant variations in the design approach. A novel system is described, with a computer-programmed tunable RF source, that tunes rapidly through all the frequencies of a nanosecond pulse spectrum, makes individual "CW" measurements, stores them, and finally computes a synthetic echo. Target signatures can be "recognized" by calculating correlation functions. Experimental results are presented.

The complex indicated angle technique, applicable to monopulse radars, is being investigated as a means of overcoming the serious degradation of elevation measurement caused by multipath when the target is within a beamwidth or so of the horizon. This technique makes use of the quadrature-phase component of the normalized difference signal, as well as the in-phase component. Results of analysis and computer simulation have been published previously. This paper reports results of a test program using a slightly modified AN/FPS-16 monopulse tracking radar and a simulated target. The results to date indicate a potential for high accuracy, though there are limitations as to the applications for which the technique appears feasible. A computer program has been developed to perform the elevation estimate and to resolve ambiguities.

Three microwave garnet phase-shifter designs are used in the AEGIS weapons system. The microwave design is straight-forward except that the toroid assembly is potted with silicone rubber to increase its power-handling capability and the magnetizing wires are shielded with a spiral-wrapped wire to prevent the propagation of higher order modes. The driver circuit uses a new "flux-feedback" concept for improved accuracy and employs monolithic circuits, hybrid circuits, and discrete components. Mechanical and electrical design of the interfaces with mating components are important cost considerations and the chosen designs are described in detail. Several techniques for improving production yield are discussed and a table of production statistics is provided. Performance histograms and data averages as a function of time and operating frequency are also presented.

Previous work on the second-order contributions of radar sea echo by Hasselmann and Barrick is generalized to include the effect of capillarity (i.e., surface tension) in the hydrodynamic part of the transfer coefficient, the lossy dielectric properties of the sea, and the angle of incidence and the polarization of the electromagnetic radiation. The present theoretical results apply to the backscattering of electromagnetic radiation from water waves that are gravity or gravity capillary waves. The introduction of surface tension in the analysis allows for second-order resonant interactions of the gravity capillary wave components. To include resonant interactions of gravity waves, the analysis must be extended to higher order. In general, resonant interactions produce higher-order contributions in the Doppler spectrum at the frequency of the first-order Bragg line that represent the nonstationary and non-Gaussian properties of the water surface. Furthermore, because of the different dispersion relation of gravity capillary water waves, the secondary lines of the second-order Doppler spectrum now are shifted toward the Bragg frequency and 2½ times the Bragg frequency. Numerical results are presented from our generalized theory for various radar and sea (water surface) parameters.

The AN/UYK-17(XB-1)(V) Signal Processing Element (SPE) is a high performance computer system being developed at the Naval Research Laboratory for radar, sonar, and communication applications. To perform signal processing tasks efficiently, the SPE comprises multiple functional units that execute different processes in parallel. Due to the inherent parallelism in signal processing tasks, horizontal microprograms are used to control the functional units [references 5 and 6]. This report overviews the SPE, describes the Signal Processing Arithmetic Unit (SPAU) in detail, discusses ANIMIL-the microprogramming language for representing SPAU microprograms, and illustrates the use of the ANIMIL translator with a simple microprogram. Companion documents describe the SPAU simulator program (reference 3) and the formal syntax and semantics of the ANIMIL language (reference 4).