• Use of Sonobuoys in Ocean Earthquake Studies

      Reichle, Michael; Bradner, Hugh; University of California (International Foundation for Telemetering, 1975-10)
      U.S. Navy anti-submarine-warfare telemetering sonobuoys have recently become an important tool in the study of earthquakes at sea. Earthquake ground motion converts to sub-audio compressional waves in the water and is detected by the sonabuoy hydrophones. The frequency-modulated sonobuoy signals are monitored with commercial VHF receivers on shipboard, aircraft or land, and are recorded on f.m. magnetic tape or strip chart. Subsequent analysis of the seismic signals gives information on location and depth of the earthquake as well as direction of fault motion, stress release and other characteristics of the event. The accuracy of epicenter location is usually limited by the precision of ship navigation but may also be limited by uncertainties in sonobuoy position measured from the ship. Events large enough to be detected on land have been located with better accuracy by sonobuoys than by the land arrays. This paper describes the techniques of using sonobuoys for earthquake research, and gives results of observations of microearthquake swarms in the Gulf of California along the extension of the San Andreas Fault.
    • Atmospheric Propagation Effects on a Laser Ship Mast Detector

      Curtis, Harold O. (International Foundation for Telemetering, 1975-10)
      The performance of a laser gate ship mast detector is evaluated. The laser gate consists of transmitting optics and laser on one side of a shipping channel and receiving optics and detector on the other side of the channel. Expressions relating the probability of detection and the false alarm rate to laser power, noise, visibility or atmospheric attenuation of the beam are developed. Finally, at power levels meeting safety standards and for useful probabilities of detection and false alarm rates, the visibilities which limit system performance are determined as a function of laser gate path length. The gate, at visible wave lengths, will function at visibilities only slightly less than the path length. In the next step, the expected performance of the laser gate using a CO₂ laser radiating at 10.6μ in the infrared is analyzed. The extinction coefficient, which is only a fraction of that in the visible case, is estimated for poor visibility conditions (RVR = 1,000 ft.) from a combination of attenuation measurements relating attenuation to total water content and meterological results relating visibility to total water content. Then, for the infrared system, the same arguments as above are invoked and, in this case, it is shown that the infrared system will provide the required performance at much longer path lengths.
    • Advanced Communications Experiments for Spacelab

      Ehrlich, Eugene; NASA Headquarters (International Foundation for Telemetering, 1975-10)
      The joint NASA-ESA Spacelab project offers the space engineer the opportunity to develop and test advanced communications technology in a new environment. The large volume and weight carrying capability of the Spacelab, plus the presence of an astronaut-engineer, means that large-diameter deployable antennas can be developed; multiple antennas operating at differing frequencies can be employed for propagation experiments and the detection of radio frequency noise sources on earth; and comparative, side-by-side telemetry experiments can be performed employing differing modulation techniques. The zero-gravity, high altitude and frequent flights into space make Spacelab a new tool for the communication engineer to employ for telemetry/ communications research.
    • System Alternatives for the Public Service Satellite Consortium

      Janky, James M.; Potter, James G.; Lusignan, Bruce B.; The Federation of Rocky Mountain States, Inc.; Stanford University- (International Foundation for Telemetering, 1975-10)
      The purpose of the Public Service Satellite Consortium is to foster the shared use of satellites as a distribution mechanism for social services in health and education for public and private non-profit users. The utility of a consortium lies in its ability to aggregate a large number of small, diverse users into a market group which can then share the costs for the space segment and take advantage of the economies of scale in procurement of ground equipment. A summary of the technical analysis of the alternatives for both the space and ground segment equipments is presented, along with cost estimates. The recommended configuration consists of 20-watt transponders and on the ground, eight- to fifteen-foot diameter antennas, using parametric amplifiers. The capital cost for the electronics alone for a Community Antenna is under $9,500 in quantities of 1000 units. This low relative cost makes it possible for many new users to benefit from satellite technology.
    • Application of the LANDSAT Data Collection System in Alaska

      Anderson, Duwayne M.; McKim, Harlan L.; U.S. Army Cold Regions Research & Engg. Lab. (International Foundation for Telemetering, 1975-10)
      LANDSAT data collection platforms have been interfaced with a variety of environmental and water quality sensors to test performance, reliability and versatility of the LANDSAT data collection system. Signal conditioning interfaces were required for sensors selected to measure: ground, soil and air temperatures; wind passage and speed; snow accumulation and ablation; pore water pressures; salinity; pH; dissolved oxygen; and water stage. System performance was found to be excellent; system reliability was high. Considering technical aspects only, exploitation of this satellite system for automated environmental and water quality data collection is hindered most by the relatively immature state of sensor and interface development. Notwithstanding, well prepared, two man field parties had no difficulty in deploying DCPs with their associated antennae and sensor subsystems in remote subarctic locations. Environmental data acquired at the various sites are being used in the assessment of the environmental impacts associated with the proposed construction of two hydropower dams on the Susitna River in interior Alaska, on the effects of impoundments over permafrost, and in assessing the effects associated with the construction and operation of the trans-Alaska pipeline.
    • Evaluation of a Random Access System with Hardware Simulation

      Delmas, G. G.; Centre National d’Etudes Spatiales (International Foundation for Telemetering, 1975-10)
      The purpose of this study is to solve the problem of the determination of the exact capacity and performances of a satellite location and data collection system using random access. Here is described the method we apply in the particular case of the ARGOS system; the TIROS-N and NOAA-A to G satellites will be equiped with the ARGOS on-board experiment and will ensure an operational service from 1978 to 1985 at least. The results we obtained are significantly better than the first estimations and should allow us to increase the number of the platforms.
    • L-Band, 1.2 m Parabolic Antenna-Noise Temperature Measurement

      Taylor, Ralph E.; Hill, James S.; NASA, Goddard Space Flight Center; RCA Service CO (International Foundation for Telemetering, 1975-10)
      Extensive antenna-noise temperature measurements at 1.6 GHz (L-Band) were made using a 1.2 m (4 ft. diameter) parabolic dish antenna mounted on the Flying Bridge of a modern 15,690-ton, commercial-container ship owned by the United States Lines. Both in-harbor and at-sea radiometer measurements were made that indicated a steady background, antenna-noise temperature value slightly less than 70 degrees kelvin (K) at elevation angles of 5°, and greater, at 1.6 GHz. A comparison of theoretical and measured values indicate excellent agreement within about 5K for at-sea data. These measurements should be especially helpful to RF equipment designers of maritime, L-Band shipboard terminals for operation with the two, geostationary, maritime satellites, Marisat-A and -B.
    • Performance of Some Block Codes on a Gaussian Channel

      Baumert, L. D.; McEliece, R. J.; Caltech's Jet Propulsion Laboratory (International Foundation for Telemetering, 1975-10)
      In this paper we use a recent technique of Chase to evaluate the performance of several block codes, notably BCH codes of lengths 63 and 95, on a Gaussian channel. We conclude that such codes are close to being serious competition for convolutional codes on this channel.
    • Asymptotic Performance of Three Hard-Limiting Noncoherent Correlator-Envelope Detectors

      Viterbi, Andrew J.; LINKABET Corp. (International Foundation for Telemetering, 1975-10)
      Three suboptimal correlator-envelope detectors are analyzed for the noncoherent detection of one of M signals. Suboptimality is introduced in each case by hard limiters which serve the dual purpose of providing automatic gain control (AGC) and simplifying mechanization. The first two, bandpass limiter preceding the detector and hard limiter in each channel, are well known and included for comparison. The third which is like the second, but with the additional feature of comparison weighting of the limiter outputs, is shown to exhibit an asymptotic performance within 0.25 dB of the bandpass limiter.
    • Intersatellite (Nd:YAG) Laser Communications; A System For The 1980's

      Barry, J. D.; Wright-Patterson AFB (International Foundation for Telemetering, 1975-10)
      It is now a certainty that laser communication systems will be operating in space within this decade. The development of a laser communications satellite package began this fall and is to be launched in 1979. The system is to operate at 1000 megabits per second. Laser communications technology has proceeded from purely exploratory research just over five years ago to the successful completion and operation this year of an engineering feasibility model of the satellite system. Laboratory tests have verified the system capability at a serial data rate of 1000 megabits per second. Thermal and vibrational tests have been successfully completed to the test levels of the Defense Meteorological Satellite program.
    • Data Collection Using Adaptive Phased Array

      Noji, T. T.; AIL (International Foundation for Telemetering, 1975-10)
      Adaptive Ground Implemented Phased Array or AGIPA provides a rapid and cost effective means to read out and interrogate a very large number of earth based sensors. AGIPA locates an array in space but locates all of its beam forming and beam steering network on the ground; thereby providing multiple high gain beams to be formed with minimal complexity in space. AGIPA offers: * Less total system cost by placing a high gain array on a central data collection system and reducing the cost of each of the thousands of sensors. * Rapid data collection due to electronic beam steering as well as through formation of multiple beams. * Nulling of unintentional RFI that can disable the entire data collection system.
    • The Influence of an Ambient Magnetic Field on Magnetic Tape Recorders

      Jorgensen, Finn; TRW Systems (International Foundation for Telemetering, 1975-10)
      Magnetic recorders are susceptible to external magnetic fields and hence prone to data degradation. This is primarily observed in instrumentation (space and ground) and computer recorders, where little or no shielding of the heads is provided. The magnetic core material in the heads attracts flux lines and will with certain orientations concentrate these in the record, play back or erase gaps. During recordings a foreign field may therefore be superimposed on the intended recording field and may cause errors in the form of phase shift and dc offset; these affects are agravated when AC bias is used in the recording process. If an external field is present during playback only, partial or complete erasure may take place. One external field is always present: The earth s magnetic field which has a magnitude of roughly one Gauss (or Oersted). The writer is not aware of any errors per se caused by this field, but it has numerous times caused difficulties in achieving a perfect demagnetization of heads (An oscillating and simultaneously decreasing field from a degausser does then in essence record a permanent magnetization into the heads, which in turn will result in noisy and distorted recordings). Other fields are man made, such as originating from heavy currents in cable harnesses. The analysis presented in this paper was undertaken to establish susceptibility limits for a field generated by a magnetic attitude control system for spacecrafts. This is illustrated in Figure 1, where three orthogonal electromagnets on board a spacecraft generate a magnetic moment (M), variable in magnitude and orientation. The attitude correcting torque (T) on the spacecraft is expressed as the cross product between this moment and the earth's field. Recording equipment may be located within a few feet of the center of the attitude control field, which must be limited in magnitude or the recorder shielded to avoid data errors and/or erasure.
    • Prospect for International Standardization

      Henriques, Vico E. (International Foundation for Telemetering, 1975-10)
      The prospects for international standardization depend largely on activities of a number of official and semi-official international programs for standards. Many of the national standards developed by the technologically advanced countries are proposed for international standardization and the process of compromise and modification is necessary to make specific standards acceptable on a broad basis. A second area of dialogue is necessary for education so that the parties to a standardization effort are capable of talking at the same level of technological detail. And, thirdly, the specific types of standards that are needed fall into areas which range from easily quantifiable to agreements on communication and national standardization are on a continuum which ranges from technical refinement to preliminary discussion and candidate standard identification.
    • Performance of Coded MFSK in a Rician Fading Channel

      Modestino, J. W.; Mui, S. Y.; R.P.I. (International Foundation for Telemetering, 1975-10)
      The performance of convolutional codes in conjunction with noncoherent multiple frequency shift-keyed (MFSK) modulation and Viterbi maximum likelihood decoding on a Rician fading channel is examined in detail. While the primary motivation underlying this work has been concerned with system performance on the planetary entry channel, it is expected that the results are of considerably wider interest. Particular attention is given to modeling the channel in terms of a few meaningful parameters which can be correlated closely with the results of theoretical propagation studies. Fairly general upper bounds on bit error probability performance in the presence of fading are derived and compared with simulation results using both unquantized and quantized receiver outputs. The effects of receiver quantization and channel memory are investigated and it is concluded that the coded noncoherent MFSK system offers an attractive alternative to coherent BPSK in providing reliable low data rate communications in fading channels typical of planetary entry missions.
    • The Mars Penetrator Telemetry and Control System

      Bentley, R. D.; Campbell, A. B.; Sandia Laboratories (International Foundation for Telemetering, 1975-10)
      A new method for exploring the planet Mars has been proposed* that will use ground-penetrating vehicles to carry scientific instruments below the Martian surface. The subsurface performance of various sequences of complicated experiments poses challenges in the design of the telemetry and control links. This article describes the overall mission, the penetrator, the constraints imposed by the mission and the penetrator, and a design for the telemetry/control system. This design uses a microprogrammed microprocessor; the sequences of commands are stored in a Read-Only-Memory (ROM), and a particular sequence is initiated by transmitting from the Earth the address in the ROM that contains the first of the commands for the specific sequence to be performed. Data from the experiments are stored in a memory for later transmission to an orbiter that serves as a relay station for the command and data links with Earth.
    • The Geostationary Operational Environmental Satellite/GOES/Imaging Communication System

      Baker, W. L.; Savides, J.; Aeronutronic Ford Corporation (International Foundation for Telemetering, 1975-10)
      The SMS/GOES Satellite obtains day and night weather information from synchronous geostationary orbit by means of (a) earth imaging, (b) collection of environmental data from ground based sensors, platforms, and (c) monitoring of the space environment. SMS-1 and SMS-2 have been in orbit for 17 months and 8 months respectively and are presently taking full earth disc images in the visible and infrared every 30 minutes. SMS-1 is positioned to cover the eastern portion of the United States while SMS-2 is positioned to cover the western portion. This paper provides a general overview of the imaging communication portions of the SMS/GOES, related to the image data encoding and transmission as well as the method of the data time multiplexing and the manner in which the scan line to line synchronization is achieved.
    • Telecommunications, Health and Education

      Christenson, Ralph P.; Mountain States Health Corp. (International Foundation for Telemetering, 1975-10)
      Prior to 1971 there were many experiments conducted in order to demonstrate or test the feasibility, acceptance and effectiveness of communications technology applied to health care and education systems. Within the past year two groups of experiments were completed. One, utilizing terrestrial broad band systems, included seven separate applications. The other, which utilized the National Aeronautics and Space Administration's Applications Technology Satellite Six (ATS-6), had five experiments in health care and education. Each of these experiments is briefly described. Further experimentation is needed with special emphasis being given to the impact of technology on human systems. There is growing acceptance of the fact that demonstrations of feasibility are no longer needed. This particular session is concerned with "Telemetry for the Benefit of Mankind." I will assume that telecommunications is not excluded and that I can spend my time in describing some of the applications of communications technology to health care delivery and health education. I will not attempt to include all applications but will limit my attention to those that seem most timely and effective. Since all applications that will be mentioned were experimental in nature, concerned largely with feasibility and effectiveness, cost-benefits were incidental considerations.
    • On The Concatenation of Self-Orthogonal Codes

      Wu, W. W.; COMSAT Labs (International Foundation for Telemetering, 1975-10)
      The concatenation of convolutional self-orthogonal codes with threshold decoding is suggested on the basis of extensive error run length statistical observations at the outputs of the decoders. Simulation results are reported and some discussion is provided.
    • Tape Tracking and Handling for Magnetic Tape Recorders

      Paroby, Walter; DiSilvestre, Raymond; NASA, Goddard Space Flight Center (International Foundation for Telemetering, 1975-10)
      One of the critical performance and life limiting elements of a spacecraft tape recorder instrumentation system which has received little attention in technical literature is magnetic tape tracking and handling technology. This technology is required to understand how to gently transfer tape from one reel to another with proper alignment and a desirable uniform velocity at the read and write transducer heads. The increased demand for high data rate (i.e. multi-track spacecraft recording instrumentation systems), coupled with performance under extreme environmental conditions, requires a thorough knowledge of the various parameters which establish an optimum designed tape tracking and handling system. Stress analysis techniques are required to evaluate these parameters substantiated with test tape tracking data, to show the effect of each parameter on a tape recorder instrumentation tracking system. The technology is applicable to ground type tape recorders where the detrimental effects of edge guidance can be eliminated.
    • Digital Clock Recovery Scheme Masks Tape Errors

      Welch, James P.; Odetics, Inc. (International Foundation for Telemetering, 1975-10)
      The bit error rate (BER) of the tape recorder is a primary factor in determining the overall accuracy of a space to ground PCM data link. The ultimate goal is to obtain a recorder BER signature that is dependent solely on tape quality; however, in practice, the BER may be several orders of magnitude worse than the goal. Usually this occurs when the data transfer rate is not preserved during dropout intervals - intervals where the net signal-to-noise ratio is insufficient to guarantee valid data cell boundary detection. This paper investigates tape dropout signatures and addresses the problem of maintaining time coherency between reproduced data and clock assurance throughout the dropout interval. A digital approach is presented that utilizes a dual threshold detector in conjunction with a clock recovery generator. The generator is synchronized to the tape signal by a clock, N-times the data transfer rate, coherent with the transport servo reference. Implementation of the approach is discussed for two popular PCM formats. The effectiveness of the approach as a function of cell boundary detection, system signal-to-noise ratio, and transport time base error (TBE) is considered.