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In the course of the past year or so, several papers have been presented here and abroad dealing with the utilization of transponders in ship's navigation. Multiple usage transponder systems are available as aids for both navigation and target recognition by Radar. Extensive research for additional uses of transponders is continuing on a broad scale in the United States and similarly in Great Britain and Holland. A simple system is needed which can operate on present day ships, now-today-with today's personnel. This system must be commercially feasible, in cost and maintenance, and be compatible with presently used instrumentation on board the average ship. The year by year rising losses in life and ships caused by collisions demand it. One proposed system is presented here.

A detailed analysis is made of a laterally displaced interrogator sidelobe suppression (SLS) radar beacon antenna system. This method is recommended as a very economical solution to the FAA requirement for installing interrogator SLS capability at operating beacon systems where no provision had been made for interrogator SLS. The analysis was verified by an actual field test at a joint use (Department of Defense/Federal Aviation Agency) radar site at Sault Ste. Marie, Mich. Sidelobe suppression was practically complete and neither time displacement nor blockage was discernible as predicted by the analysis.

A mathematical model to study target image return frequency spectrums in Doppler radars is described. The model includes the effects of eclipsing, sea surface slope distribution, and surface reflectivity characteristics. The procedure of calculations has been computerized and the analytical results are compared to flight-test values obtained from flights over the ocean. The calculated values of amplitude-frequency spectrums of target image returns correspond reasonably well with the respective recorded flight-test data.

We assume that the backscattered electromagnetic far-field of a perfectly conducting scatterer is known for all aspects and for frequencies greater in magnitude than some positive number m . Then using standard integral equation techniques, we show how numerical instability enters into the Bojarski-Lewis inverse scattering method. Since the assumed knowledge of the backscattered field is even more complete than can be expected with radar, these results show that for radar applications the Bojarski-Lewis method is numerically unstable. Moreover we show, as expected, that the degree of instability depends directly upon m . The more low frequency information we haves (i.e, the smaller m is), the more stable the method is. In the concluding remarks is noted a recent constrained Bojarski-Lewis method that overcomes much of the instability of the original unconstrained method studied here.

The problems of measuring reliable E-region electron density vs. height profiles with a vertically pointing, pulsed incoherent scatter radar are discussed, and profiles from heights of 90 km upward observed at Malvern are presented. The minimum above h/.sub max/E is more pronounced in winter than in summer, and the overall average density in the minimum is 92% of N/sub max/E. From the observationai point of view profiles showing an unresolved sporadic-E layer seen merely to be an extreme case of the normal type. Many layers are present in the E region at night; the behavior of these is erratic except for the principal layer centered just below 100 km, which may be meteoritic in origin. Incoherent scatter offers a new method of investigating the effects of solar flares in the 100 to 130 km range; observations taken during a flare, and also during a partial solar eclipse and on a magnetically disturbed day, are described. (auth)

The present understanding of auroral morphology has been developed in a large part from a vast accumulation of all-sky camera photographs taken at many stations around the world. In order to further our understanding of the concepts of the auroral oval and the auroral substorm and their relation to influences on our atmosphere, one needs to express these concepts in terms of the latitudinal distribution of the type and energy of the associated incident particles. In this review, data are presented on precipitating particles in the evening and midnight sectors in relationship to the electron trapping boundary motion within the substorm. The complex height distribution of ionization associated with particle precipitation shows some of the possible complexities in the interpretation of incoherent scatter radar data obtained in the auroral regions. Data obtained by modern satellite imagery can provide the auxiliary data needed to understand the particle effects in the polar regions. The rapid temporal and spatial changes in the aurora are seen in data from rapid scanning photometer systems and high sensitivity color television systeins. The general review of these data attempts to show that local auroral dynamics and the phase and global extent of the auroral substorm imply drasticmore » changes in the incident particle energies. These in turn produce variable atmospheric effects of direct concern to all incoherent scatter radar studies of the neutral and ion composition, temperature, and motion of the earth's atmosphere. (auth)« less

A new large incoherent scatter radar system has been proposed as the principal element in a binational center for studies of the upper atmosphere. The radar has been designed to yield a sensitivity comparable to the best now available and yet provide a latitude coverage of the F region of ±13°. The radar shall comprise a 100-m diameter parabolic reflector antenna that can be tilted in the magnetic meridian plane by ±85° from the zenith. This antenna will be coupled to a UHF pulse transmitter with a peak power of 10 Mw, and will serve for both transmitting and receiving. Two auxiliary fully steerable antennas will be located northeast and northwest of the main antenna and will also receive the signals. This will enable the velocity of the ion drift to be studied, permitting measurements of neutral winds, electric fields, and fluxes of ions into or from the magnetosphere. The auxiliary antennas will form 10 coplanar pencil beams, so that these drift measurements may be made at 10 heights simultaneously. The paper describes how the above concept was developed and the work of selecting a site for the radar. By locating the main station near L = 4, and the auxiliary stations about 550 km distant, it will be possible to measure the electric fields in the F region over the range 3 ≤ L ≤ 8 to an accuracy of ±2 mv m−1. Thus, the radar should be able to map the electric fields produced by substorms at auroral and subauroral latitudes. In addition, the properties of the ionosphere and many parameters of the atmosphere will be determined over the altitude range 100 to 1000 km.

A multipulse correlator system for the Chatanika, Alaska, incoherent scatter radar is described. The system utilizes a hardware correlator unit that can deliver as many as 40 8-bit by 8-bit lagged products every 20 μsec. The particular lags at which products are computed are patch-wire programmable, and the range gates at which data are taken are set arbitrarily under computer control. The system operates with a fixed bandwidth of 50 kHz, so that the maximum range resolution is 6 km. To obtain sufficient lag resolution for operation at 1290 MHz, we compute lagged products at other than the nominal subpulse spacing. An example of the correlator operation is given.

HF radar signatures have been synthesized from a time-dependent Gaussian ion cloud using a three-dimensional ray-tracing progam that can take into account both electron collisions and the earth's magnetic field. The ion cloud model is based on the theory of ambipolar diffusion and the model parameters are based upon the observations made during a barium cloud test conducted at White Sands, New Mexico. Ray-tracing results have been generated for both ordinary (O) and extraordinary(X) modes as well as for the “no-field” case. The results, presented in the form of a time-history of the Doppler shift and the scattering cross section, are found to be quite similar for all three cases. Relative to the O mode, the X-mode variations lag in time and obtain a maximum cross section which is greater only by about 2 db. The variations for the no-field case fall in between that of the O and X, but closer to the O mode. The results show that the cloud is extremely defocussing with an estimated defocussing factor (relative to free space) for the X mode increasing from 7.6 × 103 to 1.85 × 107 over the interval 5 to 190 sec of cloud's life. The ray-tracing signatures are compared to those synthesized by means of a hard expanding ellipsoid method with a view to evaluating the importance of underlying ionization. The effects are found to be such as to introduce a significant time lag in Doppler history and to cause a cross section reduction by a factor that builds up with time from 5 db to more than 30 db. A comparison drawn between the observed and the ray-tracing signatures leads to the conclusion that good agreement between the two can be expected only when the clouds experience either slow or no deformation and striation but not otherwise.

Solid-state array radar is of gyeat current interest because of the inherent reliability of solid-state devices and the concomitant promise for improvement in system reliability. However, no extensive reliability base has been established for solid-state devices employed under radar operating requirements. In this paper some of the important factors bearing a device reliability are treated. Accelerated life tests under RF conditions are presented for L-band power transistors. Preliminary life-test and failure-analysis data are also presented with recommendations on how the information can be used by the radar systems designer.

A technique to reduce radar pointing errors due to glint using frequency agility and amplitude weighting is presented. The reduction in rms tracking error is developed into an equation dependent upon the original glint tracking error, ?g, and the number of returns weighted, N. The rms tracking error is thereby reduced approximately by a factor of N. Finally, the equation formulated allows one to evaluate the reduction in glint error versus the number of frequencies chosen for frequency agility.

The identification and classification of radar targets is facilitated by a newly developed technique based on measurements of the differential phase shift of the target scattering obtained at harmonic phase-locked frequencies. These phase differences are independent of target range and relative motion. It is mathematically proved that for a smooth conducting body in the Rayleigh region the copolarized terms of the scattering matrix have zero phase shift. Based on this, the absolute target phase can be measured. The differential phase shift between two harmonic frequencies has been measured for various types of targets. The experimental results indicate that the differential phase shift is a useful parameter for classifying or identifying targets, and one that can be readily measured in practical radars.

A systematic, thick refraction medium approach to calculating ionospheric radar refractive effects by means of propagation-related integrals yields equations valid to second order in the tangent of the propagation angle with respect to the straight line between source and target. Significant differences are found from more intuitive developments currently used. When more than one propagation path exists between source and target, alternate propagation paths cannot be located reliably by the propagation integral method. However, inclusion of the higher-order terms responsible for the alternate solutions does significantly improve the accuracy of the primary path solution when those terms can be estimated accurately in a strong refraction situation.

Lacking Compass, sextant, chronometer, radio, radar and inertial navigation aids, “ancient mariners” relied on an observed knowledge of the prevailing winds, tides, and currents; the habits of birds, particularly sea birds; the discontinuities that exist where the sea meets the land; and the stars (1,2). A particularly well developed use of the “natural means” of the Marshallese (3, 4, 5). These Micronesian navigators devised an aid, artistic in execution, but near scientific in design and based primarily on water surface conditions.

the vector analog computer (vac) is a new radio navigational instrument which enables a pilot (1) to fly a rectilinear course either on or off the Victor airways with no appreciable lateral displacement, (2) proceed directly to any given latitude and longitude with exact positional information at all times, (3) navigate directly to any specified holding point and then hold the pattern precisely, (4) make the transition to an ILS approach with extreme versatility, and (5) assist radar traffic controllers by providing more precise information about his aircratt's position in the traffic picture than radar can provide. VAC offers continuous readings of position, bearing, distance, and ground speed with signal reception from only one VORTAC station at a time. After proceeding beyond the range of the VORTAC transmitter it can still navigate for relatively long distances on mechanical memory. It is a superior anti-collision device, is readily adaptable to all aircraft from helicopters to jets, and is capable of directing an automatic pilot independently of the magnetic directional information normally required in beam guidance systems. This paper discusses the limitations of present radio navigation systems, offers a list of criteria for an airborne navigational director with the simplicity and accuracy of visual reference, and then explains the principles of design and operation of the Vector Analog Computer.

The measurement of the radar cross section of full-size targets in flight presents some unique problems. The techniques employed to maintain the dynamic range of the signal, facilitate data handling, and control the target aspect, all contribute to the efficiency with which the requisite data may be gathered and reduced. The approaches taken in solving these problems are discussed in connection with the U. S. Naval Research Laboratory (NRL) dynamic measurement radar. This system is specially designed for simultaneous pulse-by-pulse measurements at L, S, and X bands permitting a high degree of polarization flexibility. Data reduced from film records, when combined with program-derived aspect information, enables a graphical description of radar cross section to be plotted as a function of target aspect. Data from measurements of a C-54 aircraft have been plotted in this manner and show the variation of σVV, σHH at L and S bands, and σVV, σHH, σVH, σHV, σRR, σLL, σRL, σLR at X band. Operating experience with this system indicates the practicability of performing dynamic measurements.

The scattering matrix of a target generalizes the scattering properties to include a description of their dependence upon radar polarization. The matrix may be determined directly through two successive transmissions at orthogonal polarizations, with reception of each at both of the polarizations. In the laboratory, it is possible to eliminate the requirement for phase measurement by an indirect technique using successive measurements at six polarizations (five of which may be linear). In the case where results are to be applied to linearly polarized radars, it is sufficient to determine the "linear restricted matrix" by six linear measurements. Analysis is provided and measurement technology described and evaluated for both classes of indirect measurement.

This paper reports on progress in signal design that has led to improvedresolution capability in radar and communication systems without theuse of complicated signal-processing techniques.Two approaches to the problem of improving resolution capabilityare made. The first approach emphasizes the need to produce sharplypeaked autocorrelation functions. The optimum signal amplitude infrequency is specified to accomplish this, and the spectral density ofthe deterministic signal is shown to satisfy a homogeneous Wiener-Hopfequation. The second approach emphasizes the need to producelow and flattened cross-correlation functions, in order to distinguishthem (since they correspond to error outputs) from the sharply peakedautocorrelation functions. With the use of stationary phase integration,a detailed method for producing any desired cross-correlationamplitude is presented. In particular, the techniques necessary to producesinusoidally modulated cross-correlation functions are discussed.These tools are applied to a realistic N-signal processing system,and the resulting optimum signals are shown to be amplitude-modulatedchirped sinusoids. Detailed examples for physically justifiablesystem parameters are included.

A maneuvering synthetic aperture radar in squint mode, during a loosely piloted maneuver, is simulated with presence of various navigation system errors. The error sources investigated place emphasis on short-term effects, involving platform servo transients, noise and quantization in accelerometers, interaction of angle pickoff uncertainty with the displacement from platform to radar antenna, and uncertainty in this displacement itself. Simulation results are accompained by interpretive discussion, and followed by suggested areas for further study.

Progress in coordinating the design of airborne radar equipment with the airframe is discussed, emphasizing such basic design characteristics as accessibility, form factor, heat dissipation, altitude, shock, vibration. R-F noise and primary power supply. A review of the scope of present-day installation problems follows, giving specific examples of coordinated design. Suggestions for improving current design practices include an early exchange of information among all agencies concerned, close liaison as the design unfolds, and throughout, an appreciative understanding of each others problems.

A radar speed meter operating on doppler principle has been designed and fabricated to measure the speed of vehicles plying on the roads. It comprises of a 2K 25 klystron as a transmitter, a waveguide type leaky wave antenna radiating energy in a beam of 8° in azimuth at 20° to the length of the waveguide which is aligned parallel to the road. The received echo from the moving vehicle crossing the beam is separated by a hybrid T and fed to a detector which is already receiving the reference signal. The doppler output is amplified, limited and is used to drive a multivibrator. The resultant train of pulses is counted by a frequency sensitive network, and the output voltage calibrated in speed is displayed on a meter. The whole unit is mobile and works on car battery. It can measure speeds from 10 to 100 km/hr ± 2 km/hr. Error in speed measurement is not appreciable with ±2° misalignment of the antenna.

The mechanism by which electromagnetic waves are scattered from the sea surface is studied herein. Principal applications for such studies occur in over-water communication channels and radar. Predictions based on rigorous formulations for diffraction from a (moving) time-space periodic surface are correlated with the experimental results of other authors. Such predictions explain the existence of strong coherent scattering from the sea surface in nonspecular directions (grating lobes) and also anticipate the appearance of well-defined, harmonically related, frequency shifts (time-space harmonics) in scattered signals observed in these experiments. On the basis of such manifestations of the periodic nature of the sea surface, a model is formulated for use in calculation of the angular power spectrum of scattered electromagnetic waves. This model, accounting for spatial coherence effects, assumes for the fluctuation of heights on the water surface a Gaussian distribution with a narrow band-pass (nearly sinusoidal) spatial spectrum. Calculations of the angular, scattered spectrum due to this model show strong predominantly coherent wave summation in directions corresponding precisely to the grating lobes of a purely periodic structure of period equal to the center period of the band-pass spectrum. Spectral (angular) spreading increases with increased bandwidth of the spatial spectrum of the surface. Calculations for the present study are made on the basis of a perfectly reflecting boundary and hence do not display the proper distinction of polarization expected for a completely realistic model. The results, however, display the spectral charactral characteristics necessary to explain strong scattering in nonspecular directions by a random surface.

A new technique is described which provides for precision angle tracking of celestial radio sources with a conventional monopulse antenna receiving system. It is shown that this technique is readily adapted to angle tracking radars. The features of conventional monopulse operation are preserved while permitting precise angle tracking of noise sources when signal to noise ratios are much less than unity. Measurements, using a four-horn monopulse feed with a 28-foot parabolic reflector and a "monopulse radiometer" produced the characteristic monopulse angle detection functions when using the sun, the moon, and Cassiopeia A as boresight reference sources. Precision measurements were made to 8 arc second under varying weather conditions using 28-foot radio astronomy antennas. The accuracy of the measurements were limited by the antenna angle encoders, consequently no conclusions are drawn with regard to the absolute accuracy of the measurements. The celestial coordinates of four discrete radio sources and the equations for coordinate transformation to local elevation and azimuth are contained in the Appendixes.

This paper presents results of an early study of the influence of parameters of a pulse radar system on its sensitivity. More specifically, it describes an experimental determination of the absolute value of minimum pulse signal visually detectable through random noise with a probability of 50 per cent for a wide range of the following parameters: pulse-repetition rate r, pulse length t, intermediate-frequency bandwidth B, and video bandwidth b. The following empirical formula expresses the results of the investigation with considerable accuracy: 1/ 1 \/ 1670\ 1/ 6 Vmin =-E. B112I1 +-1 ) 2 \ tB/ r/ where V min is the minimum detectable pulse voltage and E n is the noise voltage per unit intermediate-frequency bandwidth of the receiver. The application of the results to the design of search radar systems is briefly discussed.

In numerous applications it is necessary to observe a target in flight by radar for a short interval and compute its origin or destination. The present-day techniques are mostly dependent on observation of two close points on the trajectory and the transit time of the target between the two points. A new method has been evolved to give a solution from any single point on a part of the trajectory seen by an autofollow radar and is under investigation.

The sun is, after the moon, the simplest major astronomical body to reach by radar, and it is a more interesting object for study than the moon or the planets. In this paper, the process of reflection from the sun is investigated theoretically, together with the manner in which the echo intensity would be expected to depend on the various parameters of a radar system. It is shown that the detection of sun echoes appears technically possible, but a radio-engineering project of considerable magnitude is involved. Orders of magnitude of planetary echoes are also briefly discussed, and a reference is made to several astronomical studies which could be carried out with a very high-power radar.

A method is discussed for tracking the radar cross-section centroid of an ensemble of scatterers, using a raster scan observation technique. Estimation of the mean-squared dimensions of the ensemble is also considered. A maximum permissible beam separation is defined for the scan. Expressions for the bias and variance of the centroid estimates are given. Advantages of the approach are that individual scatterers need not be resolvable, and that the number of beams is independent of the number of scatterers.

Some factors that influence radar target detectability on a cathode-ray tube at high ambient light levels, such as occur in fighter airplanes, have been investigated. The signals considered are those that are intensity-modulated, as in B scopes and PPI. The problem is considered to consist of three parts that should be investigated separately: 1) the ambient brightness at which the indicator shall produce detectable signals, 2) the target spot brightness or intensity required for detection in this surround, and 3) the conversion of electrical signals into visual signals in the CRT. In this paper only 2) and 3) are discussed. It is found that with an intensity-modulated display, target detectability is determined by the spot intensity rather than by the spot brightness. The brightness of a conventional CRT shows an early saturation, but the intensity increases uniformly. Neither brightness nor intensity is a linear function of the radar parameters.

To realize full benefit from a radar, the analyzed echoes must be strong and sharp. Two options are available: Either the transmitted burst must be an intense, short pulse (often not a propitious arrangement) or the onus can be put on the receiver to process the echo into something more than it appears to be. One method for ``upgrading'' the received signal beyond a feeble echo from a not-too-powerful transmitted beam is acoustooptical processing, in which the reflected radar beam is converted to an acoustic wave that is used to modulate a light source. Then with the appropriate operation on the modulated light, the radar echo input is correlated against an optical filter. Of the two acoustooptic correlator classes described here, one works well below 150 MHz and the other is appropriate for frequencies above 150 MHz.

A recent work calculated the probabilities of detection and false alarm for the mean and median detectors for the log-normal and contaminated-normal descriptions of sea clutter. This correspondence extends the previous work by first calculating the performance of the trimmed-mean detector and then calculating the detection performance of all three detectors when the target exhibits Rayleigh fluctuations. Finally, a simple example is used to show that the optimal beamwidth of a radar need not be the smallest obtainable beamwidth.

The development of an unambiguous unit-distance code configuration for automatic altitude reporting via the ATC Radar Beacon System is described. This code provides for compatible altitude reporting in increments of 100, 250, and 500 feet within one common system. The code is developed by using Karnaugh mapping techniques. Some assumptions and requirements are set forth to provide guidance for the determination of the most desirable code. A brief presentation of a developmental code in use in the United Kingdom is also given. It is concluded that the flexibility of the unit-distance code affords a satisfactory compromise which can satisfy the objectives of the various users.

An effective forward step in terminal area air traffic control has been accomplished by development and installation of Radar Approach Control (RAPCON) Center and control tower prototype facilities described. Esoteric complexes detailed provide airport and approach controllers with radar and communication implementation of manual aids to jet and propeller driven traffic control procedures and techniques. Equipment reported also serves as manual backup and override facilities capable of eventual expansion to fully automatic air traffic control system operation dictated by high-speed jet performance characteristics.

This paper presents a method of greatly simplifying the processing of received signals from antenna arrays through the use of a coherent optical system for signal processing. It is shown that a coherent optical system is ideally suited for carrying out beamforming operations. Several other advantages of coherent optics for this application are also discussed. A major result is a technique for forming several unambiguous beams simultaneously by correlating the signals from two linear arrays. The coherent optics technique permits this operation to be carried out with extreme simplicity.

Rocket vehicles are being used to expel passive wind sensors in the altitude range of 100,000 to 300,000 feet. The sensors are tracked with S-band and X-band radars to determine wind direction and velocity. Both chaff and metalized parachutes serve as wind sensors and AGC voltage recordings made on both X-band and S-band radars during tracking periods are presented. The recordings are calibrated in decibels above the radar minimum discernible signal and plotted vs slant range. A short discussion of the effects of chaff dispersion is included. Although chaff dispersion deteriorates the effectiveness of the target at a rate of about 20 db/hour, it is concluded that the effective radar target size of the sensors and the slant ranges over which they are employed are quite compatible when AN/MPQ-12 and AN/MPQ-18 radars are utilized.

Air traffic information collected by long range radars is available to the CAA at the radar sites. This information will be remoted to the air route traffic control center. A theoretical study is made here of resolving power and the information rate inherent in the air traffic, radar video signals, displays, and various transmission techniques. Air traffic provides the basic information and radar video establishes the maximum information rate for the system. On the other hand, a display can show only a limited amount of this information. But if the display magnifies a small area, it can show all the information the radar collects. Between the radar and the presentation, the information may be transmitted by a wide band communication channel that transmits all the radar video information or it may be compressed by analog, digital or manual methods so that it can be transmitted over a much narrower communication channel. The final choice of system components will be decided by the requirements of the basic problem for resolution, off-centered displays and the needs of the traffic controller.

This paper describes some of the early developments in the synthetic aperture technique for radar application. The basic principle and later extensions to the theory are described. The results of the first experimental verification at the University of Illinois are given as well as the results of subsequent experiments. The paper also includes a section comparing some of the important features of real and synthetic aperture systems.

This paper is intended to serve both as an introduction to radar cross-section measurements and as an introduction to the several measurement papers that follow in this issue. We discuss the contribution that experimental work makes to theoretical studies. The history of cross-section measurements is reviewed. Some terms are defined, and the major measurement problems are discussed. It is pointed out that the various range geometries and measurement techniques in use today were based on the approach used to solve the basic measurement problems. Some details are given of the more popular present-day measurement systems, i.e., CW, pulsed, FM-CW, Doppler, and the standing-wave ratio method.

A simple Markov process model of binary, digitized radar clutter returns is assumed. Probability distributions for the number of hits in n observations are developed for small n with a binary parameter describing the process derived for Rayleigh distributed clutter. Tables of distributions are included, along with an example to show the effects of correlation on the false-alarm probabilities of a sliding-window detector.

One of the more difficult requirements to meet in the design of radars is that of accurate angular measurement. In tracking radars the azimuth and elevation of a target can be measured to a high degree of accuracy by a nulling method. Two of the most practical methods for obtaining angular accuracy in search radars are discussed in this paper. The first method is an interferometer technique employing either two receiving antennas for each dimension of angular measurement with two frequencies of transmission for the resolution of ambiguities, or three receiving antennas positioned relative to one another so that the equivalent effect is achieved with only one-frequency transmission. The second method is a combination amplitude comparison and interferometer technique in which the ambiguities are resolved by the amplitude comparison system. An analysis of each of these systems has been made using a statistical approach in which equations are developed relating the probability of error for a specified angular accuracy to SNR power in the receiver. Curves are presented which show this relationship for a 100 to 1 beam-splitting ratio.

This paper is concerned with the navigation of a manned space vehicle during its powered deboost phase of flight prior to landing on the moon. An inertial measurement unit (IMU), which operates continuously, is provided on board the vehicle along with an altimeter and a doppler radar. The basic problem of interest is to determine the best way to navigate the vehicle with these instruments, considering factors such as equipment operating ranges, data rates, random and bias measurement errors, terrain anomalies, and computational complexity. The navigation systems presented are based on the least-squares estimation techniques developed by Kalman and Battin. Up-to-date estimates of the vehicle's state are obtained by comparing altimeter or doppler-radar measurements with IMU-derived estimates of the same physical quantity. The key to the estimation process is the determination of the best weighting to use on these measurement differences in the updating procedure. Several different sets of weighting factors for use in the deboost phase are developed in the paper, using minimization of mean-squared estimation errors as the basic performance criterion. Bias errors in the IMU measurements, uncertainties in the knowledge of the orientation of the radar antennas relative to the IMU, and anomalies of the lunar terrain are assumed to be the predominant navigation-system error sources. The major differences between the weighting factors result from the particular model employed for the navigation sensors, the model used for the lunar terrain, and the methods used to account for measurement bias errors in the weighting-factor computations.

Propagation errors along paths between an array radar and a distribution of targets cause degradations in angle measurements and detection range. The overall objective of the research described in this paper was to analyze and demonstrate the use of conjugate reflections for compensating adverse effects of path errors. The effect of reflecting the conjugate of an incident wave is described mathematically and is demonstrated by computer simulation. Repeated conjugate reflections are shown to result in the formation of a single beam usually focussed on a target highlight. Echoes from this spatial reference, or "beacon" are shown to provide the means by which aperture phase errors may be effectively compensated. Results of radar simulations include two-way patterns computed for an example involving a distribution of three-point targets and half-wave-length Gaussian aperture errors. Without compensation a gain loss of 12 dB is computed; with error correction, based on echoes from an adaptively focussed beam, the two-way pattern is within a small fraction of a dB of the ideal pattern. The effect of noise on adaptive beacon forming was considered for a case involving one target. Repeated conjugate reflections improve signal-to-noise ratio as long as the effect of noise is less than the effect of aperture dephasing on the power reflected back to the target. An example is presented in which signal-to-noise ratio at the output of the receiver combining network is increased from 4 to 11.8 dB.

The equivalence of the vector addition, cross-correlation, and filtering approaches to deriving synthetic array patterns and analyzing processing techniques is demonstrated here. A mathematical model is defined which establishes a geometry, a transmitted and received signal, and a general synthetic array weighting function. A preliminary analysis of this model derives the signals received at the flight-path points where radar pulse transmission and reception occurred, and the effects at these flight-path points of the synthetic array weighting function. The weighted, received signal expression is then summed over the array, and the resultant shown to be a vector addition, a cross-correlation integral, or a filtering operation depending on the changes of variable and formal manipulations employed.

This paper describes the techniques and the measured radar return from "phantom targets" using 8.6 and 4.3- millimeter radars. The radar returns are compared to the measured back-scattering cross section of water drops, insects, steam and other materials at 8.6-mm wavelength as measured by a CW radar at this wavelength. Within the limits of the conditions used in the laboratory, it was impossible to produce returns from synthesized refractive index gradients of sufficient magnitude to account for those noted on the radar. It is concluded, therefore, that for the millimeter wavelengths and the short ranges considered, the observed phantom returns were due to solid or liquid particles in the atmosphere.

Noncoherent Doppler permits determination of the ground course as the azimuth of a null in the clutter Doppler returns and, therefore, can be a frequency insensitive adjunct to a pilotage search radar, especially where weight and/or power is at a premium. This stands in contrast to the customary coherent Doppler navigators which relate the frequency changes upon reflection, fore and aft, to the drift angle. An X-band self-coherent Doppler implementation developed that 88 per cent of the drift-angle measurement was within ± 1° of a concurrent optical measurement.

This paper describes some preliminary results in a study of a twin-channel frequency-modulated radar which is capable of measuring both the range and bearing of a target from a stationary aerial system consisting only of one transmitter and two receiving elements. The basic operation of the system is described along with some experimental results for range measurement. Also the proposed extension of the work to examine the bearing resolution of the system is outlined.

The use of a two-lobe monopulse radar for measuring slant range to the surface of the earth in the absence of discrete targets is analyzed. It is shown that tracking dispersion can be considered as the resultant of two components. One component is independent of range and results from the finite pulse length and gate length and the random nature of the return signals. The other component is due to receiver noise and increases as the signal-to-noise ratio decreases. The dispersion component independent of range is shown to be proportional to the pulse length and tracking gate length. The variable dispersion is shown to be proportional to the five halves power of the range and the three halves power of the cotangent of the depression angle of the antenna boresight axis. Performance calculations for a specific radar are carried out and compared with experimental data.

This paper deals with the cumulative detection probability of a search radar when it is scanning uniformly. This is the probability that a target, approaching the radar at a constant radial velocity, is detected at least once by the time it reaches a given range, as distinguished from the more common blip-scan ratio (a single-scan detection probability). It is shown that for constant-velocity targets the range for a given cumulative-detection probability varies as the cube root of the power-aperture product, rather than as the fourth root. Curves of cumulative detection probability, as a function of normalized range, are given for three different target scintillation models. Also, curves of optimum (normalized) frame time, are given as a function of the desired cumulative detection probability for each of the three target scintillation characteristics.

Techniques are presented for the approximate calculation of optimum midcourse fixed- and variable-time-of-arrival velocity-correction schedules. The theoretical results are compared to those of a simulation program which utilizes Earth-based radar and onboard sextant tracking data processed with a Kalman filter for two typical interplanetary transfets. It is shown that the agreement between theory and simulation improves as the amount of radar data processed is increased and that the theoretical optimum timing equations provide an accurate first estimate for generating interplanetary midcourse velocity-correction schedules.