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This paper reports on part of a general investigation that has been carried out to determine the feasibility and limits of performance of high‐data‐rate underwater digital data communication. Specifically, the paper deals with the amplitude fluctuations that are encountered when high‐frequency 0.8‐msec duration pulses are transmitted under short‐range shallow‐water conditions. In the paper, the results of an analysis of experimentally measured amplitude fluctuations are presented. The results, which are presented in the form of amplitude‐frequency spectra, autocorrelation functions, and probability density functions, are interpreted in terms of the prevailing climatic conditions, and the results are related to existing relevant theories of fluctuations.Subject Classification: 30.20.

ERTS; MSS data of Obon area, Montalban region, Spain were clustered into 14 non-supervised cluster classes. Statistical analysis of frequency distribution of these cluster classes in different units of interest for samples of 25, 50, 100 and 200 pixels was carried out. The results indicate that the variability of distribution is more in rock unils, and a sample size of 100 pixels represents nearest to the mean. The variability is less in non-rock units (e.g. water) and a sample size of 50 pixels is the optimum, at the present level of classification.

An ocean-bottom seismometer capsule containing a 1-Hz vertical seismometer and triggered digital recording system has been developed and tested off the coast of San Diego. The output of the seismometer is continuously digitized at 64, 128, or 256 samples per second. The digital data is mixed with a time code and passed through a 256 sample shift register which acts as a delay line. It is then mixed with synchronization characters, serialized, encoded, and recorded on a SONY TC800B tape recorder which is turned on when a seismic event occurs. The event trigger occurs when the seismic signal jumps to at least twice the time-averaged input signal. Data are recovered using the same recorder for playback and a decoder which provides an analog output for field data interpretation or a digital output for computer analysis. The capsule itself falls freely to the ocean bottom. After a predetermined time it is released from a 150-lb steel tripod and floats to the surface. A dual timer and explosive bolt system provides a high recovery reliability. A number of seismic events have been measured in field tests and the system has proven to be extremely simple to check out, diagnose, and deploy.

This concise paper reports the result of a study on a multiplexing scheme for digital data transmission and switching which can handle both anisochronous and isochronous data traffic of various mix, mainly in one digital channel of PCM primary multiplex level (e.g., 1544 kbits/s) and corresponding time-division switch (TDSW) of data-switching equipment. The study aims to determine a unified scheme which is economical and flexible for intercity heavy-traffic data links, to accommodate a wide range of data speeds. The paper describes various multiplexing schemes and analyzes their features in terms of frame structure, synchronization time, error-correction capability, compatibility with signaling, hardware complexity, etc. A bit-interleaved multiplexing scheme is chosen as suitable and is applied in a laboratory model of a digital data switching system, the DDX-1 System.

A vehicleborne magnetometer enables high resolution magnetic surveying to be conducted with savings in time and labour. Established airborne systems are unsuitable for closely spaced traverses in high resolution mapping. To utilise the full sensitivity of currently available magnetometers on land it has been necessary to carry the instrument by hand and to record individually the data at discrete stations. Described is a method for simply overcoming the magnetic perturbation encountered in close proximity to a vehicle and thus enabling high fidelity analog or digital data to be recorded while driving over the ground. The unit is capable of a rapid rate of traversing, combined with the possibility of immediately investigating the geological significance of an observed anomaly. The technique lends itself ideally to "on site" data presentation providing "visual signal enhancement" of weak spatial anomalies hidden in temporal noise. Quantitative interpretation of the ground level profile may be automatically performed by applying a Hilbert Transform method and use of the "magnetic signature" of rocks is suggested for regional geological mapping.

The studies to measure the unsteady flow by means of a combined probe were shown in the previous papers. However there have been left two problems unsolved: One of them is the convenient procedure to process great many time-series data, and the other is the way to confirm the accuracy of the measuring systems. These means were established by using a digital data processor, improving the experimental devices and developing the computer program. In this paper, the calibration procedure of a combined probe is presented and the error estimation in flow measurements is discussed with the application of characteristic polynomials which are derived from the regression analysis for the calibration data using digital computer. To formulate the probe characteristics as polynomials is greatly useful in measuring unsteady or steady multi-dimensional fluid flows.

The utilitarian aspect of the Digital Data System is discussed with emphasis on performance objectives that will be important when data communications is inserted into a system of data processing. Objectives for the dependability and quality of data communications are quantified and evaluated in terms of their impact on data processing. Characteristics of the several types of channels available are described in detail along with operational features of particular importance at the interface between data communication and data processing.

The mechanical design of equipment required to build the Digital Data System is described. Economic and technical constraints influencing partitioning, electrical interconnection, and styling are related. An overview is given of the hardware used for terminating loops, multiplexing data streams, and testing for system performance.

Effective analyses of performance for detection schemes that optimally decode digital data in the presence of intersymbol interference have been slow in coming. Recently, however, Forney has given an upper bound on the bit error probability for maximum-likelihood sequence estimation. Starting from a standard geometrical framework, we give a much simplified derivation of this upper bound. Our derivation places the validity of this important bound more in evidence in that the concepts of whitened matched filter and error event are not introduced.

The problems of designing and implementing LSI systems for the processing of 2-D digital data, such as images or geophone arrays, are reviewed and discussed. This discussion encompasses both FIR and IIR digital filters and with respect to the latter, the issues of stability testing and filter stabilization are also considered. Techniques are also presented whereby such filtering can be accomplished using either 1 or 2-D LSI systems.

The Digital Data System is synchronized by means of a network in the form of a master-slave tree. Functioning data links are used for distribution of synchronization signals and timing is recovered from the data stream. The master timing supply sets the frequency for the entire network. Each major node contains a nodal timing supply with an extremely long time constant, which phase-locks to the incoming data signal. The nodal timing supply contains frequency memory and sufficient accuracy to free run satisfactorily for several days if its inputs fail. A local or secondary timing supply is designed for operation in distant nodes of the tree. Each timing supply provides common clock signals to all DDS equipment in the office in which it is installed. All timing supply designs include a high degree of redundancy for reliability purposes.

The characteristics of long-period (20 to 200 sec) earth noise have been investigated at the 11 high-gain, long-period (HGLP) seismograph stations using as many as 3 years of analog seismograms and digital data from these stations. A major contribution of this study is the significant increase in the number of long-period earth-noise spectra that are available from areas of vastly differing geological and tectonic settings outside the contiguous United States. This information is important to the study of the long-period portion of the spectra of earthquakes and to the discrimination of earthquakes and underground explosions. A significant feature of earth-noise spectra based on data from all the HGLP stations is a minimum between about 25 and 45 sec. This minimum spectra level is most pronounced at sites with more than 200 m of overburden. The level of earth noise generally recorded by vertical-component seismographs at both the shallow and deep stations is independent of local meteorological conditions if the seismographs are located on competent bedrock and are subject to rigid environmental controls. The level of earth noise recorded by horizontal component seismographs at HGLP stations, however, is dependent on local meteorological conditions. This dependency decreases with increasing depth of overburden. The decay rate with depth of this horizontal earth noise is such that approximately 150 m of competent overbuiden is usually sufficient to attenuate about 90 per cent of the earth noise caused by local atmospheric conditions.

Network design methods are described which determine the multiplexing and digital transmission facilities required to serve a given data-circuit demand. The long-haul network design is based on the definition of a three-level network routing hierarchy, the derivation of intercity bit-stream requirements, and a technique for selecting digital transmission facilities to carry the bit streams. The distribution network design within metropolitan areas makes use of different multiplexing combinations best suited to anticipated demands and techniques for using short-haul digital facilities in an efficient manner.

Forney's asymptotic upper bound for per-bit error probability in the detection of pulse-amplitude-modulated digital data in the presence of additive white gaussian noise was obtained for the case where the duration of the intersymbol interference is bounded. In this paper, we show the validity of Forney's bound under much weaker assumptions that allow unbounded intersymbol interference.

Reliability and maintainability are important aspects of the service objectives for the Digital Data System. Consequently, maintenance planning was an essential element in the DDS development. Maintenance features provided by the system include in-service performance monitoring, protection switching, comprehensive alarms, and the means for rapid fault isolation and repair.

The dynamic behavior of a discrete-time method of synchronizing adigital data communications network is discussed. Necessary conditions for stability of some special cases are derived, and it is shown that, with a constant drift'rate of one or more clocks, the buffer stores eventually overflow, indicating the need for a modified control scheme.

A direct-reading digital ratemeter based on a relatively simple and flexible design is described. It is automatic in its range changing and, when measuring a random pulse sequence, the standard deviation can be selected by a switch in the range 0.2%–7%. Depending upon the range and standard deviation selected, the associated time constants range from 2 mS to 10 000 s. The three modes of readout provided are three-decade numeric indicators, digital data, and analogue.

Development of satellite communication systems for military use involves human factors engineering in such new areas as digital data handling and computer assistance, besides the well-known areas: function allocation, task analysis, control and display arrangement, workplace layout and personnel subsystem test and evaluation. This paper deals with contributions made during definition, design and verification of the Air Force Satellite Communication System and associated Navy and Army versions. The description of system development provides an up-to-date case study of human factors engineering problems in a military procurement setting. Recommendations are made concerning future system planning.

The local distribution portion of the Digital Data System is discussed in this paper. Baseband, bipolar transmission over telephone cable pairs is used to extend the digital channel from the serving central office to the customer's location. The performance and requirements of these local channels are presented. The design and performance of the local distribution hardware are examined. Design features include (i) automatic equalization by means of an automatic line-build-out network and (ii) control mode indication by means of bipolar format violations.

The two-stage multiplexing hierarchy developed for the Digital Data System is described. Included in this hierarchy are three synchronous time-division multiplexers and a new 64-kb/s cross-connect arrangement that offer both flexibility and simplified administrative procedures. Maintenance for the multiplexers is provided on an in-service monitoring basis and includes automatic switching of a “hot” spare in the event a fault is detected.

Rapid changes are planned and occurring in the method of controlling and monitoring the generation and transmission systems of electric utilities. New control centers containing process digital computers and digital data acquisition systems and control equipment are being constructed. New and improved methods of man-machine interface are being employed. Computers receive data from the electric generation and transmission system and accomplish control action and operate interface devices to act as a tool for the system dispatcher. These new tools improve the security and economic operation of bulk power systems. This paper describes the new control system for Commonwealth Edison Company.

Digital computer processing of nuclear medicine scintillation camera dynamic studies can help extract more diagnostic information and make possible new modes of quantitative data presentation. A simple, inexpensive, off-line digital data acquisition and processing system is designed and constructed which has proven both clinically workable and diagnostically useful.

An easily-constructed interface is described that permits acquisition and processing of data by a programmable calculator from a semi-automated atomic absorption spectrophotometer used in trace metal analysis.

We consider the situation in which digital data is to be reliably transmitted over a discrete, memoryless channel (dmc) that is subjected to a wire-tap at the receiver. We assume that the wire-tapper views the channel output via a second dmc). Encoding by the transmitter and decoding by the receiver are permitted. However, the code books used in these operations are assumed to be known by the wire-tapper. The designer attempts to build the encoder-decoder in such a way as to maximize the transmission rate R, and the equivocation d of the data as seen by the wire-tapper. In this paper, we find the trade-off curve between R and d, assuming essentially perfect (“error-free”) transmission. In particular, if d is equal to Hs, the entropy of the data source, then we consider that the transmission is accomplished in perfect secrecy. Our results imply that there exists a C s > 0, such that reliable transmission at rates up to C s is possible in approximately perfect secrecy.

A major difficulty in the development of methodologies for segmentation and classification in automatic recognition of continuous speech is the determination of objective, reliable performance statistics. Compounding this difficulty is the large amount of data necessary to make reasonably accurate performance estimates. The system to be described provides for concurrent objective evaluation of up to five independent segmentation/classification methods against a single, carefully transcribed referent. A basic assumption of the evaluator is that the systems to be compared, as well as the referent, can each use the same digital data as input. Violation of this assumption would lead to time-shift errors, and objective comparison among systems would be exceedingly difficult. For segmentation, the evaluator provides first-order statistics, at the phonetic, class and summary levels, in the form of highly concise tables for the following four types of errors: 1) Missed events; 2) Adventitious events; 3) Misplaced events; and 4) Adventitious and misplaced events. For classification, first-order statistics are derived in the form of confusion matrices at the phonetic, class and summary levels. While the system is still in the developmental process, it is operational and currently used. Examples of output will be presented.

La medición de uno de los fenómenos de más relevancia en el campo de la hidráulica; la velocidad de corrientes en canales de experimentación o en modelos reducidos hidráulicos genera la necesidad de desarrollar un equipo de precisión con tiempos de respuesta mínimos, conservando características de portabilidad para observaciones de campo. El propósito del aparato que se presenta es el de mejorar las cualidades anteriores en precisión, empleando una técnica eficiente y moderna por integración de la medida a una observación digital.

This paper presents an overview of the Digital Data System. The services to be provided are described and the premises for establishing both service and system objectives are discussed. The network concept, planning for its growth and administration, and a description of the network elements are presented as an introduction to the detailed papers which follow.

We describe a digital data acquisition system for laser scattering spectroscopy, which measures the ratio of the scattered signal to either the incident laser power on the sample cell or the total signal incident at the spectrometer entrance aperture. The incident reference that is not used to form the ratio is used to check stability of the scattering sample. This report outlines the philosophy of the technique and gives components and circuit diagrams for its implementation. Digital measurement of light

The AN/GSC-10 (KATHRYN) is a digital data terminal for use on high-frequency radio circuits. In this paper, error rate and redundancy performance are discussed. Experimental data resulting from a cross-country field test are presented.

There are many experimental situations where the response of a physical system is monitored following the application of a step function in the stimulus. The analog or digitized output signal from such experiments often consists of a noisy transient having the form of an exponential decay. In many cases, a baseline signal is not available. A simple computer method, suitable for on-line use is described for treating the digital data and evaluating the exponential time constant. The accuracy of the baseline restoration technique and of the measurement of exponential time constants in general is estimated using data simulated by the same simple computer program. The applicability of the method to other common experimental situations is discussed.

This paper considers the application of satellite relay techniques to provide communication paths for aircraft-ground communication over the ocean. It considers the feasibility of a communication system design for air traffic control (ATC) utilizing the reflex repeater as the basic satellite-borne relay device. Implementation of satellite relay techniques would permit continuous line-of-sight operation for reliable ATC digital data links and voice transmission. The paper describes the basic use of the relay system, the repeater electronics, and the communication link parameters required to accommodate the satellite-aircraft link geometries. Examples of typical aircraft-ground link calculations are presented, and the basic supersonic aircraft communication requirements and satellite contact profiles are discussed.

This paper describes a system of data editing with provisions for computer entry of flight test data as acquired by an integrated digital data system. Also described are system concepts that must be dealt with in solving problems incident to these activities. The computer station described is provided with editing control facilities that permit selection of the desired prime and commutated channels which are essential for data reduction. The editing facilities provide for the most economic use of computer and manpower effort and are so designed that they permit convenient access to all instrumented channels. In addition, peripheral equipment is described as an aid in the editing process for examining the raw data in terms of analog. quick-look, and permanent record equipment.

Development of the PDM-to-digital encoder and associated translator resulted from a requirement to preserve the accuracy of pulse-duration modulation (PDM) telemetered data. Deterioration of accuracy in the data reduction or ?playback? of such data is avoided by digitizing the data directly at the output of the receiver and recording the digitized data in serial form on a standard PDM channel of a magnetic tape recorder such as an Ampex model 309 using Ampex model 303 pulse amplifiers. The pulse duration is measured at the half-amplitude level of the PDM pulses for the digitizing process to minimize the effects of variations in amplitude and rise and fall times. Once the PDM data are digitized, no error is introduced by the PDM circuitry or wow-and-flutter characteristics of the tape recorder. Range timing is recorded on a standard channel adjacent to the PDM channel. A translator is required at the data-reduction facility to convert the digital data recorded on a conventional PDM tape recorder channel into a format suitable for computer or buffer equipment use. The translator, with associated time code reader to read the tape recorded range timing, supplies a time tag with a time resolution of 1 millisecond for each digitized data sample.

This paper describes a procedure for the digital geometric registration of digitized air photographic data. Match points are located visually and used to formulate a global linear conformal transformation for each slave picture. Each transformation then serves to segment the corresponding image into regions such that, for the implementation of the correction, all pixels within a region can be shifted by the same number of rows and columns. In other words, the actual correction is achieved by a series of local translations (zero-order transformations). Remaining problems are then the filling of holes in the output pictures and the finding of a common submatrix. The image registration which results, provides a preprocessing operation needed to combine data from multitemporal and multispectral photography.

A system particularly suitable for the on-line transmission of data derived from semi-automatic tables has been developed to measure the events of high energy particles on bubble chamber photograms. The transmission is done by radio.

A system has developed to make density measurements on particle tracks in nuclear emulsions. The output signal of a videcon viewing the track through a microscope is digitized to detect developed grains in the emulsion. This digitized information is transferred in real time to a computer which selects grains falling in the track and sums their volumes and computes parameters related to their spatial distribution. Analysis of tracks at arbitrary angles is accomplished by rotating the track image in the focal plane with a Pechan prism and by driving the focal plane through the emulsion while taking data.

The accuracy with which an airborne receiver of a low frequency radio navigation system can be located in real time can be improved considerably by combining the position information from the receiver with velocity information from a velocity sensor such as a Doppler radar. Since aircraft maneuvers and hence the dynamics of the aircraft position and velocity are not known apriori, it is advantageous to combine position and velocity in a filter having a distortionless constraint, that is, a filter whose output has no position error resulting from the dynamics of the inputs. The theory of optimization of such distortionless filters, which are by definition analog filters, has been described in the literature. However, the long range and inherently high accuracy of a low frequency radio navigation system dictate a digital filter combination. In this paper, optimum digital filters combining position and velocity information under an approximate distortionless constraint are synthesized. Four types of digital filters are analyzed and compared: filters having a single sample rate and containing zero order or first order integrators, and filters having a dual sampling rate and containing zero order or first order integrators. These filters are optimized for minimum variance in their position outputs in response to band-limited Gaussian noise in their position and velocity inputs. Position error resulting from random noise and aircraft maneuvers are derived as a function of sample rate. Curves of position error versus sampling rate for a typical low frequency radio navigation system are presented.

This magnetometer has been developed by C.S.F. (Compagnie Générale de Télégraphie Sans Fil) and C.G.G. (Compagnie Générale de Géophysique). The magnetic field is measured by an optical pumping sensor giving a frequency proportional to the field. A digital frequency‐meter delivers a reading each second with a sensitivity of ± one period (31.5 periods for one gamma). These readings are recorded on a magnetic tape recorder and on an analog TEXAS recorder. The digital data are processed on a 1620 IBM. During the flight a second magnetometer records the variation of the earth’s field in a ground station located in the center of the area surveyed. The ground record data are subtracted from the airborne data. The following data obtained with this equipment are presented: Analog record with a sensitivity of one gamma for two mm. Restitution with 1620 IBM and CALCOMP of the magnetic record to an analog record with a sensitivity of one gamma for one cm. Isogam maps with a contour interval of one gamma and some intermediate contours at 0.5 gamma.

The performance limitations on the linear control of a linear plant, due to the presence of a feedback channel with finite information capacity, are considered in this paper. This situation may arise in such diverse applications as (a) the remote control of a plant, using a digital data link for feedback, (b) where quantization errors and bit errors of a digital controller may be modelled as occurring in a noisy digital channel in cascade with an ideal controller, and (c) in human-operator modelling, where the sensory feedback channels are characterized by fixed information capacity due to neural noise. The principle result obtained is that, given the state-dimension n of the plant and the channel capacity @e, reliability function E(R), and block encoding time T> >1C, the optimum data-rate R satisfies the equation 2R=nE(R). This rate provides the optimum tradeoff between the effects of quantization errors and message errors. It is seen that R"o"p"t->C as n becomes large, but that good channel performance is retained provided that > >nT.

Crimmins et al. [1] showed how to minimize mean-square error over all 1 - 1 mappings of digital data into binary group code elements when the a priori probability of the data is uniform. This paper shows how to optimize simultaneously over all possible choices of coset leaders for the detection scheme.

The problem of transmitting digital data through electromagnetic environments of high ambient-pulse density is one of growing concern. The appearance of pulsed radar in the lO-Mw range, and sensitive receivers in the - 100-dbm range, will aggravate this situation. This paper discusses three efforts made by the government to predict the status of future environments. In all cases, the basic technique of analytical prediction calls for the solution of mathematical models by digital computer. Results from these analyses are useful to the designer of future systems as well as to the operators who must use them. The responsibility of keeping the signal congestion within bounds rests with the designer and user alike.

An idea for a time-coding analog-to-digital converter using an exponential voltage sweep is presented. The technique inherently offers the possibility of convenient automatic recalibration in order to compensate for long-term drift. Thus, the converter is particularly well suited for on-line use in automatic digital data reduction systems. Attention is paid to the calibration and use of the converter. A design procedure is suggested and the obtainable accuracy evaluated in terms of the design parameters. Some comments are made concerning the merits of the scheme as compared with the most common existing systems.

A practical and functional design is presented for the storage of radioisotope indicator concentration data in digital form on FM analog magnetic tape. The converter is designed to utilize the 12-bit parallel binary output of a Baird Atomic Digital Ratemeter (Model 425) which is converted into a 4 line 1–2–4–8 binary-coded-decimal (BCD) pattern suitable for recording on any multichannel FM instrumentation tape recording. The output levels are set at ± 1 volt compatible with Laboratory Instrument Computer (LINC) external line logic levels. The LINC is used to process the digital ratemeter data on-line and off-line in experiments dealing with tube models and anesthetized animals in which the mean transit time (MTT), appearance time (TΛ), flow (Q) and volume (V) are computed. The stability and reproducibility of the experimental digital data stored in this form far exceeds that of equivalent analog data. This design should further extend the accuracy of blood-flow and cardiac-output determinations using radioisotope indicator-dilution techniques.

A system in which the output of a digital computer is displayed as an arbitrary character on a memotron tube is described. Two sequences of pulses, each consisting of 25 pulses equally spaced in time, each either positive or negative, and all of equal magnitude, are applied to X and Y counters. Each pulse either increases or decreases the contents of the counters by one. The digital data in each counter are then converted to analog data which is applied to the deflection plates of the tube. Eight types of basic lines are traced on the screen and the characters are built out of these basic lines by continuously tracing them one after another in the proper sequence. Details of linking the system with an existing computer are described. Some advantages of the system are: (a) it does not involve any critical and complicated adjustments, (b) the shape of characters can be easily changed, (c) the operation of the system is mainly digital, and (d) the character is written as a continuous trace.