Position Of Transmitter Research Articles

Multipole borehole acoustic waveforms: Synthetic logs with beds and borehole washouts

We give a two‐dimensional (2-D) velocity‐stress finite‐difference (vs-fd) formulation for the multipole borehole acoustic logging problem. Irregular boreholes, horizontal bedding, and axially varying alteration are encompassed by the model. Excellent agreement is obtained with transform techniques for constant radius boreholes and homogeneous formations. The method is used to generate waveforms for many positions of transmitter and receiver array relative to beds and washouts as in logging. First motion and semblance techniques are applied to the waveforms to extract formation slownesses, resulting in synthetic multipole logs which demonstrate the response of ideal multipole logging tools and signal processing to several environmental effects. For monopole, compressional, first‐motion logs, residual slowness errors remain at borehole washouts after borehole compensation. These errors increase as the effective measure point in the waveforms is moved back in time from true first motion, admitting greater interference from reflected and mode‐converted waves. Errors at bed boundaries are typically smaller than those at washouts. Stoneley slowness logs are obtained by narrow‐band filtering of low frequency monopole waveforms and application of the semblance slowness extraction algorithm STC. Similar processing applied to low frequency dipole waveforms yields flexural mode slowness logs. A small correction satisfactorily accounts for flexural mode dispersion properties, yielding formation shear slowness. Slowness errors for both Stoneley and dipole shear logs at washouts and bed boundaries are quite small, typically on the order of a few percent. Borehole compensation is of marginal benefit for both of these logs since they are based on modes of the borehole rather than head‐waves.

Optimization of the distance between transducer and scatterer in hydroacoustical modeling

This work was motivated by the need to understand the effect of phase and amplitude variations on the scatterer's surface as well as the reflecting boundaries of the hydroacoustical tank on the structure of the acoustical field in modeling. It is known that the null positions of the spectral characteristics of the backscattered signals from various objects in water can yield information about their shape, dimensions, orientation, and structure. Accuracy of such measurements is affected by the amplitude and phase variations on the scatterer surface and these variations depend on the minimum distance between the transmitter and scatterer positions. Calculations of these distances for acceptable dimensions of acoustical tanks were performed. Expressions were derived to correct the minimum allowable distance to prevent time coincidence of impulses from the scatterer and from the walls of the echoic acoustical tank.

Cellular telemetry by microwaves

A process based on microwave interferometry which allows the determination of the position of a beacon transmitter, and its displacement inside a predefined area is presented. This location is defined in terms of elementary areas or cells.

Time delay techniques for satellite interference location system

Describes the development of a system for inferring the position of uplink ground stations, using existing domestic satellites, with minimal disruption of normal operation. The system uses the differential time delay of a single uplink signal passing through two adjacent spacecraft to infer the relative position of the uplink transmitter. A system for the measurement of such differential time delays is described. Since this technique alone does not provide an unambiguous determination of uplink transmitter location, the use of an interferometer to resolve such ambiguities is discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The Fixed Receiver Electromagnetic (FREM) Method for Drill Hole Surveys

The fixed receiver electromagnetic (FREM) method is the reverse of the fixed transmitter method. The receiver is fixed, the transmitter is moved, and measurements are plotted in profile or plan at the transmitter positions. In drill hole applications the method extends the way in which information can be gathered and provides improved definition of conductive mineralization. In order to predict and interpret anomaly patterns, it is convenient to invoke reciprocity and visualise the receiver as an electromagnetic source, and the transmitter as a signal measurer. Model and field results confirm that a finite conductor causes a dipolar type magnetic field anomaly, which readily gives information on the strike, dip and approximate location of the conductor. However, conductive overburden may also produce a significant down hole electromagnetic response, and a FREM anomaly that is approximately dipolar. It is therefore necessary to identify the overburden effects and perhaps attempt to remove them, before interpretation. In addition to rules of thumb, a dipole source, and a rectangular current filament source, have been used successfully for interpreting conductor geometry from FREM data. The FREM approach is novel; it complements conventional drill hole electromagnetic survey measurements. A further appreciation of its advantages as well as drawbacks will come from experience.

A new method for water suppression in the proton NMR spectra of aqueous solutions

We suggest a new method of obtaining proton NMR spectra of dilute solutes in H20, which suppresses the intense water resonance by more than three orders of magnitude. This is achieved with a sequence of short, strong radiokequency pukes designed to be insensitive to many of the imperfections of Fourier transform NMR spectrometers. High quality spectra can therefore be obtained without the need for fine adjustment of experimental parameters (pulse lengths, phase shifts, delays, and transmitter frequency). The performance of this sequence surpasses all existing methods of solvent suppression. The ability to measure routinely proton NMR spectra of Hz0 sohuions is essential for the observation of exchangeable protons that cannot be seen in D20. Much attention, for example, has focused on the NH protons of nucleic acids and proteins. The problems associated with the detection of weak solute resonances in the presence of an intense signal from the 110 M water protons have been comprehensively reviewed (Z-3). Of the various techniques devised to overcome these difhcuhies, those employing selective excitation (Z-10) are probably the most successful, the most widely used being Redfield’s 2 14 composite soft pulse (2, 6). Other approaches (II) involve presaturation, partial inversion recovery, and rapid scan cotrelation spectroscopy. Solvent suppressions of a few hundred can only be obtained by careful variation of several parameters to minimize the amplitude of the free induction decay or the spectrum baseline curvature. In looking for a more satisfactory selective pulse sequence, we have used the criterion that it must give a broad flat region of near zero excitation around the solvent frequency and yet appreciably excite relatively distant resonances. Thus small static field inhomogeneities and errors in the transmitter position could be tolerated. We were guided in this by the approximate Fourier transform relationship (5-7) between the pulse sequence in the time domain and its frequency domain “excitation spe&rum” (excited transverse magnetization as a function of offset frequency Y). A function in the frequency domain possessing the desired properties is S,(V) = sin”(rv7) with n a positive integer. All derivatives of S,(V) are zero at v = 0 up to and including the (n - I)*, thus satisfying the first part of the above criterion. The Fourier transform of S,,(V) is proportional to

Error Analysis for Relay Type Satellite-Aided Search and Rescue Systems

An analysis is made of the errors in the determination of the position of an emergency transmitter in a satellite-aided search and rescue system. The satellite is assumed to be at a height of 820 km in a near-circular near polar orbit. Short data spans of four minutes or less are used. The error sources considered are measurement noise, transmitter frequency drift, ionospheric effects, and error in the assumed height of the transmitter. The errors are calculated for several different transmitter positions, data rates, and data spans. The only transmitter frequency used was 406 MHz, but the result can be scaled to different frequencies.

Ambiguity Resolution for Satellite Doppler Positioning Systems

The implementation of satellite-based Doppler positioning systems frequently requires the recovery of transmitter position from a single pass of Doppler data. The least-squares approach to the problem yieds conjugate solutions on either side of the satellite subtrack. It is important to develop a procedure for choosing the proper solution which is correct in a high percentage of cases. A test for ambiguity resolution which is the most powerful in the sense that it maximizes the probability of a correct decision is derived. When systematic error sources are properly included in the least-squares reduction process to yield an optimal solution the test reduces to choosing the solution which provides the smaller valuation of the least-squares loss function. When systematic error sources are ignored in the least-squares reduction, the most powerful test is a quadratic form compasison with the weighting matrix of the quadratic form obtained by computing the pseudoinverse of a reduced-rank square matrix. A formula for computing the power of the most powerful test is provided. Numerical examples are included in which the power of the test is computed for situations that are relevant to the design of a satellite-aided search and rescue system.

Error analysis of a satellite interferometer navigation system

An error analysis is performed for a global positioning and navigation system which relies on an orthogonal array of interferometry baselines on board a geostationary satellite. The error analysis involves linearization of a mathematical model which is based on the relationship between the measured phase differences, the known transmitter positions, and other systematic error parameters. According to the error analysis, position accuracy is critically dependent on the baseline length and the magnitude of the random component of the measuring errors. It is shown that a satellite interferometry system with baselines of about 50 m can yield position accuracies on the order of 20 m.

Satellite Interferometer as an Advanced Navigation/Communication System

An orthogonal system of interferometry baselines aboard a geostationary satellite is considered for a variety of applications involving navigation, surveillance, and traffic control. The position determination is based on the relationship between the measured phase differences, the known and unknown transmitter positions and other systematic error model parameters using a generalized Least-Squares estimation procedure. Study of the effects of the various system and error model parameters on the position accuracy reveals that the accuracy is critically dependent on the baseline length and on the magnitude of the random component of the measuring errors. With a 50-m baseline, the obtainable accuracy at a frequency of 1.5 GHz is comparable to that of the NAVSTAR/GPS system. Several trade-offs with respect to the system accuracies, the number of users, data rates, hardware costs, etc., are examined. Simultaneous utilization of the same communication channels for both navigation and data transfer is found feasible. Based principally on the equipment requirements of potential users, five candidate or “strawman” interferometer systems are configured. The overall performance of the interferometer system is considered excellent when compared with other existing or planned navigation systems. Considering the interest and needs of prospective users for a multicapability system, this interferometry system is considered potentially viable in meeting their requirements.

An analysis of the bipole-dipole method of resistivity surveying

Bipole-dipole (B-D) resistivity mapping has been widely used as a reconnaissance method in geothermal exploration. In this technique, apparent resistivities are plotted at roving dipole receiver locations and the current source (bipole) is left fixed. Interpretation to date has been in terms of simple, layered, dike, vertical contact, or sphere models. In the case of more complicated two-dimensional models the interpretation is much more ambiguous and the detection of buried conductors depends very much on the choice of transmitter location. Since apparent resistivities taken on a line collinear with the dipole are roughly equivalent to the apparent resistivities for one sounding in a dipole-dipole (D-D) pseudo-section, the two methods have been compared for several two-dimensional models. A buried quarter space and a buried horizontal cylinder of rectangular cross section, with or without an overburden layer, have been used in the comparison. Unless the target is very shallow or close to the bipole or dipole, the resolution of the horizontal position or depth extent for the B-D method is very poor. Conductive overburden worsens the situation for both methods but the effect is more drastic for the B-D method. The spatial patterns for these models is complex for the B-D method and in fact for certain transmitter positions only subtle differences exist for the buried cylinder and buried quarter space models. Multiple sources improve the resolution of the B-D method, but many sources coupled with the high sampling density of receivers required to define the spatial patterns would greatly reduce the cost effectiveness claimed for this method. Changing the bipole orientation with respect to the strike of the models contributes little if anything to the resolution of the models. A further experiment of calculating a residual map by subtracting the half-space or layered half-space response from the response of the buried models was also unsuccessful in improving the interpretability of the B-D method. Finally, a model representative of a typical Basin-and-Range valley with and without a hypothesized geothermal reservoir shows that in more complex models the B-D map would not, in a practical survey, reveal the reservoir. From these model studies it is clear that, except for some simple geologic situations, the B-D method is not effective for subsurface mapping. Selected D-D lines would be far more useful and more cost effective.

Ultrasonic pelvimetry. A method for preliminary estimation of the pelvic outlet

Vaginal sound, with transmitter crystals of 2 MHz, is used when measuring the interspinous diameter. The echo from the pelvic wall, the effect on the measured spinal diameter by altering the position of the ultrasonic transmitter, and the influence of air or faeces between the ultrasound transmitter and the pelvic wall, have been analysed in a series of model trials on a dummy submerged in water. Thereafter clinical trials were performed on 102 women, pregnant in their 9th month. The results obtained when measuring the interspinous diameter on the ultrasonic tomogram were compared with the results obtained when measuring the same distance on a frontal x-ray picture taken using the orthographic technique according to Borell-Frenström. The method is suitable for selecting those cases with suspect constriction of the pelvic outlet for an x-ray examination by the Borell-Fernström technique.

Error analysis of the Doppler correction factor in underwater communications

One limitation to the attainment of high spectral resolution in underwater communications is the Doppler effect. In principle, this purely geometric, or kinematic, effect can be defined precisely and the attendant Doppler-generated frequency shift can be removed by suitable signal processing. In practice, however, uncertainties in knowledge of instantaneous position and velocity of transmitter and receiver always exist and constitute an instrinsic limitation to spectral resolution. An error analysis is presented here of the Doppler correction factor for underwater communication between the sonar systems of two mobile platforms whose instantaneous positions and velocities, including rotation and other accelerations, are known imprecisely. Doppler errors produced by inhomogeneities in flow structure and sound profile are ignored, but the uncertainty in knowledge of sound speed is recognized. Some simple expressions for rms and worst-case errors are derived for cases which are distinguished by the relative size of transmission time to a characteristic rotational period. An application to spectral resolution by mobile parametric receivers is mentioned.

Local Field of an Acoustic Source in a Submarine Canyon

An exploratory study is presented concerning hydroacoustic signal reception in the locale of a single-frequency CW ultrasonic source situated within an underwater submarine canyon. A first-order laboratory model of a submarine canyon is described together with the hydroacoustic studies that have been made with the simulation setup. For each of several transmitter positions within the canyon, ultrasonic reception has been recorded continuously in (transmitter-to-receiver) range for a variety of orientations and depths of receiver relative to transmitter. Although canyon geometry was arranged to be readily changeable, only canyon width has been varied thus far. Some broad inferences from our study are: (1) a submarine canyon can behave as a waveguide and channel sound almost undiminished for some distance down the canyon, both within and above its confines; (2) the canyon can act as an acoustic horn relative to sound radiation immediately above its confines; and 3) sound reception beyond the locale of the canyon can be appreciably smaller than that realized in the absence of the canyon. Quantitative results depend on the transmitter position within the canyon, canyon geometry and topography, the nature of the sound source, and the relative location of the receiver.

Application of Spherical Trigonometry to Problems in Wireless Direction Finding

Mathematical theory for tackling various problems encountered in Wireless Direction Finding is given. Primary among these problems is locating accurately—by calculation or otherwise—the position of an unknown transmitter, knowing its bearings from two known D/F stations. The theory assumes importance in high frequency D/F work, when the transmitter sought to be located may be very far off from D/F stations and over the area the earth cannot be presumed flat.

Analysis of radio signal interference effects due to ionized layer around a re-entry vehicle

The theoretical section of this paper discusses the electromagnetic properties of the ionized shock layer about a missile re-entering the atmosphere; a treatment is then given of the problem of predicting the transmission, through the shock layer, of electromagnetic waves originating on the vehicle. The major portion of this section is given to outlining the important quantitative aspects for calculating the extent of the attenuation problem. Theoretical curves are given which allow rapid prediction of the attenuation effects due to air ionization once temperature and density are specified in the shock layer. If other sources of free electrons are significant, e.g. ablation products, separate determination of the density distribution must be made. Specific results are given on certain Polaris configurations and trajectories as computed using this method; these predictions are based upon two specific transmitter frequencies. Although the method utilizes the Lorentz theory and the plane wave-plane homogeneous sheet assumption is made, the resulting estimates are shown to agree satisfactorily with signal strength records of actual re-entry tests. A quantitative discussion is given concerning the approximations inherent with the use of the Lorentz theory of conductivity in view of “strong fields” near a transmitter and the velocity dependence of collision cross-sections. A portion is given to possible solutions of the transmission problem suggested by the parameters available in various ranges of temperature and density; particular attention is given to transmitter frequency and position of the antenna. A method is demonstrated for extrapolating the results of a minimum of predictions for a given combination of radiator and re-entry body to include predictions for a wide range of altitudes and velocities.

Absorption and electron distribution in the F2 layer determined from measurements of transmitted radio signals from earth satellites

Comparison is made between measured field strengths of transmitted signals from earth satellites and those theoretically predicted when the transmitter position is in the region of maximum electron concentration of the F 2 layer, below it, and above it. The observed absorption value agrees best for a biparabolic distribution with exponential continuation with K = 8 × 10 −3 where the electron concentration is given by N = N 0 e − kh . The number of electrons per column in the upper region of the F 2 layer is deduced to be 1.5 × 10 13 electrons per cm 2. This value is compared to the findings of Burgess. Curves are given of field strengths at distances greater than 10,000 km. At distances of 16,000 km the formation of ionospheric wave guides make possible the transmission of radio signals.

An Optical Radar for Surveying

An instrument is described which uses radar techniques to make a survey of terrain. Distances are determined by measuring the transit time of pulses of light traveling between the instrument and a retrodirective reflector placed at the point whose relative position is to be found. Angles are measured by adjusting the position of the optical transmitter to obtain a maximum pip on a cathode-ray tube.

Fundamental problems in radio direction-finding at high frequencies (3–30 Mc/s)

The problems of direction-finding at high frequencies may divided for convenience into three groups, (a) those dealing with instrument itself, (b) those dealing with phenomena occurring in course of propagation of the waves, and (c) those concerned with interpretation of the bearings once the readings have been obtained.As to the instrument, the basic type of high-frequency direction-finder during the past decade has been the Adcock, using spaced vertical aerials. During the war years, attempts were made to improve performance of the simple Adcock direction-finder by the use of earth mats or arrangements of radial counterpoise wires. Some reduction of polarization error on sites of low conductivity was thereby achieved. There were advances in bearing display, particularly in regard instantaneous direct-reading types, while improvements in design components such as receivers and goniometers have resulted in all-round improvement in the performance of high-frequency ground station direction-finders.To overcome the difficulties of polarization error inherent in Adcocktype direction-finders, several types of practical spaced-loop directionfinders have been developed in recent years. These are all of the rotating coaxial-aerial type.Future improvements in instrumental design are likely to involve departure from the small-aperture spaced-aerial arrangement, and systems of wide aperture, in which the direction of the wavefront is determined by measurements made at widely separated points are forecast. Reduction of certain types of wave-interference errors, particularly those due to scattering, is likely to be achieved.Recent advances in knowledge of the propagation of waves in the high-frequency band have been concerned chiefly with ionospheric waves. A good deal of information of a statistical nature concerning the deviations suffered by these waves has been accumulated but much still remains to be done, particularly as regards a study of the characteristics and structure of the ionospheric irregularities causing deviations. During the war years various attempts to overcome some the difficulties encountered when dealing with ionospheric waves were made. Of these, the most important were the ray selection technique involving apparatus for the selection of a single ray component of complex signal) and the employment of groups or clusters of directionfinding stations in place of single stations. In the future, the use instruments of large aperture is likely to cause both of these techniques to be outmoded.Once a bearing from a single direction-finding station or a group bearings from a network of direction-finding stations has been obtained, there arises the problem of deciding what information is contained the figures as to the true direction or position of the transmitter. This is the problem of interpretation and it is essentially a statistical one. There are at least two parts to the problem, (a) to determine, a priori, the probable accuracy of the individual bearing or bearings; and (b) with this information to determine the most probable location the transmitter and establish areas within which there is a given probability of finding the transmitter. The first of these two problems is essentially the more difficult, and though there have been attempts at a solution by various schemes for “classifying” the bearings according to probable errors there is still no fully satisfactory solution. Given solution of the first, the second problem is mathematically simple, the solution being found in terms of the principle of least squares. In the future, the development of mechanical, electronic or other devices which will carry out the necessary operations automatically is likely to proceed.

The application of ultra-short-wave direction finding to radio sounding balloons

The paper describes the early portion of an investigation into the possibilities of determining wind velocities at high levels by radio methods It was prepared in the spring of 1939, but publication has been delayed owing to the important part which this technique has contributed to meteorology during the war In the intervening six years considerable progress has been made in the application of the basic principles described in this paper. An account of this later work, leading to the practical techniques now used by the Meteorological Office, will be published later. The position of a radio-sounding balloon transmitter can be determined by the aid of two direction-finders set at a suitable distance apart, together with a measurement of the altitude, which can be obtained from the barometric pressure and the thermometer units attached to the apparatus. The present paper is concerned with an investigation of the accuracy of the direction-finding technique used for the observation of bearings on the signals from radio sounding balloons during actual flight. From a knowledge of the precision of such radio bearings, the accuracy of position location of the balloon can be computed with the aid of curves given in the paper. Preliminary experiments conducted with direction-finders of both the closed-loop and spaced-aerial types on wave-lengths between 8 and 10 metres (frequencies 30 to 38 Mc/s.) showed that a reasonably high instrumental accuracy was obtainable; but that in order to utilize this to the best advantage it was necessary to install the direction-finders on very satisfactory sites. Accordingly, the experiments were continued with the aid of specially designed direction-finders of the rotating-loop type installed on two superior sites situated at the ends of a suitable base-line for balloon location work. As a result of the calibration of these direction-finding installations, it was found that the observational accuracy was of the order of 0°1. The maximum error in bearing obtained in the course of the ground calibrations at a short distance was about 1°, but successive calibrations of the installations over a three-monthly period disclosed a variation in this site error of about 0°5. The results of tests carried out on some twenty balloon flights show that, by taking mean observed bearings over each minute period, 95% of the bearings are correct to within 2° and nearly 80% correct to within 1°; the probable error of such mean observed bearings, after correction for the ground calibration, is about 0°3.