Range Sidelobe Suppression for Barker Codes

The utility of Barker-type phase-reversal codes is extended by the use of sidelobe suppression techniques that can be easily implemented in digital form. It is shown that sidelobe suppression techniques can be found where the tapped delay line used to reduce the sidelobes has only a few distinct tap weights, in which case the complexity of the digital processor is greatly reduced. An example is given where the technique is applied to Barker codes with positive sidelobes, specifically, the 13-element Barker code. If higher pulse compression factors are desired than are obtainable with Barker codes, multistage Barker codes may be used. The sidelobes then may be suppressed for any one or all of the different coding stages.     

Computed Performance of Glide Slope Arrays on Sites with Limited Ground Plane

The computed performance of four different types of glide slope transmitting arrays sited over idealized ground planes consisting of one-dimensional perfectly conducting strips of various lengths in free space is presented. The idealized ground plane approximates the practical case of a site consisting of an expanse of relatively flat ground plane ending in a precipitous dropoff or in rough diffusely reflecting terrain. The computed results show several phenomena which have repeatedly been observed.     

Elimination of electromagnetic radiation in plasma simulation: The Darwin or magneto inductive approximation

For many astrophysical and magnetic fusion applications, the purely electromagnetic modes generated by real as well as simulation “plasma” fluctuations are a source of high frequency radiation that is often irrelevant to the physics of interest. Unfortunately, a numerical CFL stability limit prevents either making c infinite or Δt large while using the usual explicit Maxwell's equations for the fields. A modification of Maxwell's equations, which provides implicitly the field components, circumvents this problem. The solution is to neglect retardation effects so that the electromagnetic propagation speed is effectively infinite. The purely electromagnetic modes in this limit evolve “instantly” to a time-asymptotic configuration about the macroscopic plasma configuration at each new time level. The Darwin or magnetoinduetive approximation effectively provides infinite propagation speeds for purely electromagnetic modes by converting Maxwell's equations from hyperbolic to elliptic in character. In practice, this is accomplished by neglecting the solenoidal part of the displacement current. The elimination of the CFL time step constraint more than offsets the substantially more complicated field solution that is required. The details of a numerical implementation of this model will be presented. Numerical examples will be given and extentions of the Darwin field solution to other plasma models also will be considered. This work was performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.     

Comparative study of spermatogonial survival after x-ray exposure, high LET (HZE) irradiation or spaceflight.

Spermatogonial cell loss has been observed in rats flown on Space Lab 3, Cosmos 1887, Cosmos 2044 and in mice following irradiation with X-ray or with high energy (HZE) particle beams. Spermatogonial loss is determined by cell counting in maturation stage 6 seminiferous [correction of seminferous] tubules. With the exception of Iron, laboratory irradiation experiments (with mice) revealed a similar pattern of spermatogonial loss proportional to the radiation dose at levels less than 0.1 Gy. Helium and Argon irradiation resulted in a 5% loss of spermatogonia after only 0.01 Gy exposure. However, significant spermatogonial loss (45%) occured at this radiation level with Iron particle beams. The loss of spermatogonia during each space flight was less than 10% when compared to control (non-flight) animals. This loss, although small, was significant. Although radiation may be a contributing factor in the loss of spermatogonia during space flight, exposure levels, as determined by dosimetry, were not significant to account for the total cell loss observed.     

U.S. operational space program for climate observations

Satellites provide two important characteristics to earth climate studies not available from other, conventional sources: (1) full global coverage, and (2) consistency within the data set. This latter arises from the fact that the satellite data are usually derived from one instrument (or at least from a small number) whereas other sources involve large numbers of separate instruments and hence exhibit a substantial standard deviation. Satellite data, of course, are more subject to bias and must therefore be carefully validated, usually via ground truth.The ISCCP and ISLSCP are examples of the increasing reliance on satellite data for climate studies. In addition to the multispectral images, quantitative products of importance are: (1) atmospheric temperature structure, (2) snow cover, (3) precipitation, (4) vegetation index, (5) maximum/minimum temperature, (6) insolation, and (7) earth radiation balance. The U.S. civil space program is presently committed to its current geostationary (GOES) and polar (NOAA) programs through this decade and to continue both programs into the next decade with spacecraft carrying improved and augmented instrumentation. GOES VISSR Atmospheric Sounder (VAS) data, presently in research status and available only for special observation periods, will become available operationally in 1987 from the current spacecraft series. GOES-Next will provide additional spectral channels, simultaneous imaging, atmospheric soundings, and possibly increased resolution starting in 1990. The NOAA follow-on spacecraft, in the same time frame, is expected to provide additional spectral channels, improved passive microwave radiometry, and possibly increased spatial resolution. The Landsat program is expected to be continued by a commercial operator following the useful life of Landsat-5. All three follow-on programs are presently at various stages of definition and procurement. Final definition may not be completed until late in 1984. However, their status as of the time of this presentation will be reviewed in detail.     

ISCCP cloud analysis algorithm intercomparison

The International Satellite Cloud Climatology Project (ISCCP) will provide a uniform global climatology of satellite-measured radiances and derive a climatology of cloud radiative properties from these radiances. For this purpose, a pilot study of cloud analysis algorithms was initiated to define a state-of-the-art algorithm for ISCCP. This study compared the results of applying the nine different algorithms to the same satellite radiance data. The comparison allowed for a sharper understanding of the process of detecting clouds and shows that all algorithms can be improved by better information about clear sky radiance values (essentially equivalent to surface property information) and by better understanding of cloud size distribution variations. The dependence of all methods on cloud size distribution led to selection of an advanced bispectral threshold technique for ISCCP because this method is currently better understood and more developed. Further research on cloud algorithms is clearly suggested by these results.     

Aerospace High Voltage Development

High voltage has been used for electrical power system generation, transmission, and distribution for over 75 years and manufacturers have been designing x-rays, radios/television transmitters and receivers for many years with excellent success. High voltage usage in aerospace equipment initiated during World War II with the advent of high power communications and radar for airplanes. About 20 years ago the first high voltage components were built for spacecraft systems. This article is to provide some insight into the status of high voltage for aerospace equipment and the differences between terrestial and aerospace system functions and the attendant problems. What are the basic differences between terrestial/commercial and aerospace equipment? The aerospace environment is defined as that significantly above the Earth's surface: From 5000 feet altitude to deep space. The basic differences are the constraints placed on the user vehicle (airplane, missile, or spacecraft). Constraints include: Atmospheric pressure, temperature, lifting capability, electronic requirements, and volume. Early airplanes needed only radios and mechanical pressurization instruments. Today's sophisticted airplanes require transmitters, receivers, controls, displays, and in the military case, special electronics. The addition of electronic devices has increased the electrical power demand from a few watts (for early aircraft) to well over one megawatt for special applications. There is the need for compact packaging to reduce weight and volume. Spacecraft with booster limitations are ever more restrictive of weight and volume then airplanes while they must maintain complete electrical system integrity for mission durations of several months to years.     

SAMBO-GEOS : Electric field measurements in the disturbed ionosphere and magnetosphere

Measurements of the electric field in the ionosphere and the equatorial plane during the pre-onset and actives phases of a substorm (March 4, 1979) are compared. Correlations and disagrements between the measurements are considered. The preliminary conclusion is reached that the model of electrojet polarisation proposed by CORONITI and KENNEL (1972) could possibly explain part of our observations.