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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.

A pulse-Doppler backscatter radar operating in the HF band was used to test the feasibility to measure ocean surface motions in the North Atlantic Ocean under a variety of environmental conditions. Using the ionosphere as a part of the propagation path, data were collected at ranges from 600 to 2200 nmi. Environmental conditions included a relatively small hurricane, a large storm, and a relatively calm ocean. The Doppler data were converted to wind vectors and compared with weather data taken at the same times and places. Preliminary results indicate that there is, in general, good agreement between wind directions as determined from the radar data and this is indicated on the weather chart at all ranges and under all of the environmental conditions encountered. The agreement in wind strengths is fair to good, but at present reliability is mainly limited to the first-hop data because of multiple propagation modes. Improvements in this technique can be expected from refinement in the theoretical models of scattering, and in developing radar operation methods that minimize multipath responses.

Interference in the form of multipath or uncooperative targets can seriously degrade the angle-of-arrival estimation accuracy of mutiplebeam processors. In this paper, the generalized likelihood ratio test is used to derive a test to detect the presence of interference for multiple beam processors. The detector performance is then analyzed in detail with respect to its dependence on signal-to-noise ratio (SNR), signal-to-interference ration (SIR), and on the relative phase between the target and interfering signals. It is shown that good detection performance can be obtained unless the phase difference between the target and interference signals is either in or out of phase.

The Skylab S-193 altimeter experiment utilizes a 10- and 100-ns pulse length, 13.9-GHz earth-pointed radar system to obtain earth-surface backscatter measurements from the Skylab spacecraft. Objectives of the experiment are to obtain precision measurements of surface profile for uses in geodesy, oceanography, and earth physics, and to measure radar-signal characteristics from an earth-orbit geometry to provide design information for future radar remote-sensors. The technical approach is that of measuring the power impulse response of the scattering surface. The hardware is designed to operate in five modes: waveform or impulse-response measurement and altitude determination; radar cross-section experiment; signal correlation experiment; 10-ns pulse-compression evaluation; and nadir-seeker experiment. This program is the first reported instance in which these quantities have been measured from orbital conditions. The experimental approach utilized and the post-flight data-processing requirements are discussed and preliminary results from the first manned Skylab mission are presented.

The monitoring of bird movements and flight characteristics by radar can contribute to an understanding of radar clutter and bird migration, can help to alleviate the hazard of collisions between birds and aircraft, and may constitute a useful form of environmental monitoring. Most conventional surveillance radars can detect birds readily but are very much limited in their ability to identify birds. The recording of amplitude and Doppler signatures, however, may allow identification as to size and type and has the potential for increasing knowledge concerning bird flight.

The usefulness of radar as an automotive obstacle detection system is currently being investigated. Possible applications of such a system presently are automatic braking and air bag actuation and eventually the totally automatic highway. One type of radar having possible potential for these short range applications is diplex Doppler radar. The microwave and electronic circuits basic to a diplex Doppler radar obstacle detection system are described in this paper. The system provides Analog outputs proportional to range, velocity, and time to impact relative to an obstacle, as well as indicating whether the velocity is opening or closing.

An X-band radar designed and built by the Naval Research Laboratory and capable of continuously variable transmitted pulse durations down to 1 nsec is being flown on a NASA Wallops Flight Center C-54 aircraft to investigate the interaction of radar altimeter signals with the sea surface. There is good agreement between the observed radar altimeter leading edge rise time for a 1-nsec transmitted pulse and the rise time predicted from the radar parameters and the sea state determined by a laser profilometer. Using a threshold tracker on 29-pulse averages for a transmitted pulse of 24 nsec, we found that the range noise varied linearly with the power level of the threshold over a considerable range. The altimeter range quantization was 9.35 cm and a minimum range noise of 3.9 cm was obtained. A comparison of pulse-to-pulse correlation observed in the radar data with that predicted by a Monte Carlo simulation is used to obtain a measure of sea surface scatterer motion.

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.

The main characteristics of the atmospheric tides observed at St. Santin and Garchy are examined and compared. It is found that the semidiurnal tide is very variable in the meteoric range (80 to 100 km) and more regular above. Some direct comparisons, corresponding to simultaneous measurements, show the same features and exhibit a good agreement in the region where the two types of measurements overlap.

An experiment is described by which the ephemeris of a near-synchronous satellite was determined from passive range observations. The data consist of the measured times of reception at ground tracking stations of electromagnetic signals which are radiated from the satellite at regular intervals. A comparison of the ephemeris to one obtained from Doppler tracking indicates an accuracy of better than 4.9 mrad rms.

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.

Ionospheric refraction is one of the factors limiting the accuracy of radar systems tracking objects in or beyond the ionosphere. In advanced systems it may be desirable to perform accurate corrections for these effects in real time, and because of the extreme variability of the ionosphere, this presupposes real time, local ionospheric measurements, e.g., by a modern digital ionosonde. The ionosonde could then be required to monitor the state of the ionosphere, compare it with model conditions, and forecast the radar refraction environment in real time. One component in this problem is the calculation of the radar refraction effects, given the ionospheric electron density profile, the apparent radar range, and look angle. Assuming that the electron density depends on height only, this paper describes such a procedure suitable for use within the Dynasonde or a similar digital ionosonde interfaced to an active radar system.

The antenna elevation control signal and the associated staticequilibrium equations are analyzed for the case of tracking of lowaltitude targets for both monopulse and conical-scanning radar. Three possible equilibrium positions of the radar antenna under static operating conditions are ascertained. The static solutions suggest certain dynamic solutions that are likely to arise under practical conditions. The extreme values of the pointing error are shown in graphical form.

Radar echoes from meteorological targets have existed almost from the time that radar was first used. In this paper, an equation is presented which relates the echo power to a characteristic of the cloud or precipitation particles within the radar pulse volume. Some examples of how radar has been used for operational purposes are given; these include a description of the utility of radar for storm detection, how radar can be used as an aid to weather forecasting for both the public and aviation interests, and also how radar can be applied to help solve some hydrological problems. Significant research results on the nature of atmospheric structure and processes as derived with the help of radar are presented. Doppler radar has played a prominent role in the investigation of storm dynamics, and high-power high-resolution radars have been used for studying the development and nature of clear-air turbulence and convective processes in the clear air. Recent trends in meteorological radars are indicated and suggestions are set forth which relate to the improved use of radar for operations.

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.

Vertical drift measurements in the topside F region at midlatitudes have confirmed the importance of dynamical processes, but it has been difficult isolating those processes due to E X B drifts from those due to neutral winds. To remove this ambiguity, three-dimensional drift measurements were made at Millstone Hill Observatory with the steerable L-band radar in conjunction with the vertical UHF antenna. The geometry of the experiment is discussed and daytime drifts are presented. Unusual lifting of the F-layer peak was observed on two occasions. A reversal in the deduced meridional neutral wind is observed in one case and an enhanced eastward electric field in the other.

Coherent high-resolution synthetic-aperture radar systems achieve their range resolution by pulse compression and azimuth resolution by compression of naturally generated FM coding due to Doppler shifts as the aircraft flies by the target. If the data is left unprocessed, it is, in effect, a defocused map of the terrain. As such, it should exhibit less dynamic range than if the data is compressed. This paper describes an experimental study to verify the above conjecture. The results of this study indicate that if dynamic range of the data link is a problem, the radar data should be transmitted in its unprocessed form. This might very well be the case for planetary mapping by means of satellites.

Recent developments in airborne Doppler and ground mapping navigation radars and ground and satellite based radio systems are described. Simultaneous lobing and slope tracking techniques can remove the well-known Doppler sea bias error in fast and slowly moving vehicles. Doppler velocity information can be extracted from coherent forward-looking mapping radars, and high position fixing accuracy can be achieved by synthetic aperture radars. In radio navigation systems, such as Loran, Omega, and satellite systems, direct-ranging and differential techniques greatly reduce the geometric dilution and propagation effects which have plagued conventional radio navigation systems. The advantages gained by mixing of the data from these and other navigation sensors in a digital multisensor system are discussed and approaches for processing these data are suggested.

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

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 objectives of the Apollo 17 Lunar Sounder Experiment (ALSE) were to detect subsurface geologic structures, to generate a continuous lunar profile, and to image the moon a radar wavelengths. The first objective is generally impossible on Earth, but is possible on the moon because of the very low EM attenuation found in lunar rocks. A three-wavelength synthetic-aperture radar (SAR) operating at 60 m, 20 m, and 2 m (5, 15, and 150 MHz) was designed to attain these objectives. The design choices reflected a balance of scientific requirements versus Apollo mission and hard-ware constraints. The most difficult choice was that of wavelength, since longer wavelengths have the potential for deeper subsurface penetration at the expense of depth resolution. Shorter wavelengths enhance the ability to generate surface images and accurate profiles. The sounding requirement led to a system requirement for large dynamic range and precise sidelobe control. The radar data from the lunar mission were recorded on photographic film in a conventional SAR format, and were returned to Earth for processing. A combination of optical and digital processing and exploitation techniques was applied to the scientific interpretation of the data. Some preliminary results from the lunar mission have been obtained. The system design and data exploitation techniques developed in support of the ALSE experiment show considerable promise for eventual application to earth-resource survey radar systems.

The effect of soil moisture on the radar backscattering coefficient was investigated by measuring the 4-8 GHz spectral response from two types of bare-soil fields: slightly rough and very rough, in terms of the wavelength. An FM-CW radar system mounted atop a 75-ft truck-mounted boom was used to measure the return at 10 frequency points across the 4-8 GHz band, at 8 different look angles ( 0\deg through 70\deg ), and for all polarization combinations. A total of 17 sets of data were collected covering the range 4-36 percent soil moisture content by weight. The results indicate that the radar response to soil moisture content is highly dependent on the surface roughness, microwave frequency, and look angle. The response seems to be linear, however, over the range 15-30 percent moisture content for all angles, frequencies, polarizations, and surface conditions.

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.

Over-the-horizon (OTH) HF radar using sky-wave propagation via refraction by the ionosphere is capable of detecting targets at distances an order of magnitude greater than conventional microwave radar limited by the line of sight. Some of the characteristics, capabilities, and limitations of OTH radar based on the experience of the MADRE radar as developed by the Naval Research Laboratory are described. Also discussed is the application of OTH radar to air-traffic control and to the remote sensing of sea conditions.

The principles of opto-acoustic signal processing and the advantages of using opto-acoustic correlators to process radar pulses are explained. Various delay line configurations, their design and limitations, are briefly reviewed. These include delay lines folded in two and three dimensions. A prototype correlation receiver employing a 12 segment 350 μs delay line is described.

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.

The design and construction of an electronic-scan phased-array antenna system for use with a clutter-mapping radar system is described. The phased array is capable of \pm-20\deg of electronic beam steerng and full hemispheric mechanical steerability. It is composed of 780 short-backfire radiators with a total gain of 36 dB. It is vertically polarized and has phase-monopulse-tracking ability. The electronic beamforming and steering is controlled by a digital system using a PDP-11/20 general-purpose computer system. The same computer is used to control the digital clutter-mapping system, which is composed of an A/D converter, multiplexer, digital tape recorder, high-speed disk storage, and an intensity-modulated graphic recorder.

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.

Temperature and ion composition results obtained during the eclipse of 7 March 1970 at Millstone Hill are presented. The temperature variations appear to be controlled by the high degree of magnetic activity present on the eclipse day. Ion composition variations may be explained in terms of photochemical processes and the distribution of ionizing radiation across the solar disk. The data indicate the quality of ion composition determination by incoherent scatter radar, and it is concluded that these data are more useful when averaged in quantity to determine diurnal, seasonal, and solar cycle variations rather than short-term temporal variations on a given day.

Various shortcomings of modulated subcarrier attenuator calibrators are discussed. Very precise attenuation measurements on short lengths of waveguide have been obtained by inserting into the subcarrier channel a tuned reflectometer system which contains a waveguide switch for setting the zero. Using this technique, total spreads of less than 0.0013 dB have been obtained at 4 GHz in 10 completely independent measurements on the same unknown. The full theory of this method is given in the Appendix. The total range of a modulated subcarrier system has been extended to over 100 dB by using a 1-W microwave oscillator and placing in the subcarrier channel a rotary attenuator with very good resettability and a fully matched two-path configuration that contains two waveguide switches and the unknown.

The influence of the oscillator noise on the minimum detectable signal of a Doppler RADAR with a self-mixing IMPATT-diode oscillator is evaluated. For very short-range RADARs, it is the AM noise which limits the signal-to-noise ratio and thus the range.

The possible use of multiple wavelength radar systems to determine raindrop size distributions is examined. Pairs of radars at 1, 3, and 10 cm, respectively, are considered; the method involves measurements of rain reflectivities at two wavelength and at two range intervals separated by about one km. Assuming a general exponential form for the drop distribution, equations are derived relating the distribution parameters to the measurements. From these analytical forms the sensitivities of these parameters to radar inaccuracies are examined. The results show that one needs combined 2-radar accuracies of 1 dB to get even marginal drop distribution accuracies. Such accuracies are considered impractical at present. Other impractical constraints implicit in the results are the assumed uniformity of reflectivity over distances of approximately 1 km, and the requirement to average as many as 104 independent power samples.

Test results and key principles are given for a radar altimeter designed for meteorological balloons. The instrument, which weighs 160 g and consumes 0.7 W, will fill a gap in meteorological, sensing using balloons-an area where pressure altitude was formerly the preveiling reference. The instrument is basically a delay-lock radar utilizing a superregenerative RF stage. Long-term absolute accuracy of ±10 m and short-term stability of better than- 2 m rms were measured at altitudes of 20 km.

The modified generalized sign test processor is a nonparametric, adaptive detector for 2-D search radars. The detector ranks a sample under test with its neighboring samples and integrates (on a pulse-to-pulse basis) the ranks with a two-pole filter. A target is declared when the integrated output exceeds two thresholds. The first threshold is fixed and yields a 10-6 probability of false alarm when the neighboring samples are independent and identically distributed. The second threshold is adaptive and maintains a low false-alarm rate when the integrated neighboring samples are correlated and when there are nonhomogeneities, such as extraneous targets, in the neighboring cells. Using Monte Carlo techniques, probability of false-alarm results, probability of detection curves, and angular accuracy curves have been generated for this detector. The detector was built and PPI photographs are used to indicate the detector's performance when the radar is operated over land clutter.

In this paper an exact closed-form expression for the radar detection probability is derived and results are plotted for a frequency diversity radar receiver. The receiver model performs post-detection integration on all received pulses in all diversity channels. The target model assumed is the slow fluctuating Rayleigh-distributed (Swerling case I target) scatterer. Each of the M frequency diverse channels receives N amplitude-correlated returns to give a total of NM post square-law detection integrations. The tabulated data falls between the two extreme cases, that for which all the returns are amplitude-correlated and that for which each return is independent. The plotted results fall close to the figures obtained through simple empirical relationships.

The quality of coherent radar images is affected by several factors inherent in the target scattering phenomenon and in the radar system. Certain of these factors, such as resolution, image fluctuation, assumed amplitude cell statistics, noncoherent smoothing, background noise, and the film response, are investigated in detail. Simple statistical models of an extend target are constructed in order to simulate images and to show how these effects are related. It is shown that resolution is the dominant factor that affects image quality. The relative importance of all other factors is highly dependent on resolution.

The UK incoherent scatter system operates in two modes. The monostatic pulsed system has been in operation since 1968, and a summary of the results obtained in this mode is given. The full multistatic CW system has been operating since September 1972 and among the preliminary results are measurements of the total vector of velocity drift.

A series of experiments was conducted with HF and VHF radars at White Sands, New Mexico, during the months of October 1970 and June 1971 to search for direct RF backscatter from ionospheric irregularities produced by the Platteville heater. The observations were made from White Sands because radars at this location view the heated volume normal to the earth's magnetic field lines. Direct echoes from the heated volume were unquestionably observed. Returns were obtained at frequencies up to the highest available at the HF radar site: 30 MHz during the first series of observations and 54 MHz during the second. The echoes were observed only after sunset, at times when the local plasma frequency over Platteville was of the order of 5 MHz at the layer maximum. The total radar scattering cross section of the heated volume was found to decrease with increasing frequency and to vary from less than 104 m2 (the minimum detectable cross section) to 109 m2, depending on frequency and time of day. The Doppler spectrum of the returns indicated that the drift velocity of the scatterers through the heated volume was greater than the relative velocity between scatterers and comparable to the drift velocity of natural irregularities at midlatitudes.

The production of topographic maps requires two kinds of information. First, the detail to be placed on the map sheet must be identified. Second, the positions of the various objects and features must be measured in three dimensions. Current airborne radar technology provides the means to satisfy both of these requirements in adverse weather and at any time, day or night. Radar used specifically for this purpose employs synthetic-aperture techniques to obtain fine resolution measurement in two dimensions and interferometry to obtain the third measurement.

The paper describes a special combination of high resolution, high accuracy, solid-state radar equipment with a sophisticated computer operated automatic acquisition automatic plot collision avoidance indicator. Technical characteristics and special features that make this equipment particularly suitable for the newer higher speed Merchant Marine vessels are described. A description is given of the separate displaying of high resolution radar and automatic navigational data. Information is also presented concerning application and performance features that make it particularly well suited for service aboard ships.