Solar-cometary relations and the events of June–August 1972

Evidence for correlations of brightness fluctuations of heads of comets with solar and solar-related phenomena is presented, and the examples of Comet Schwassmann-Wachmann (1) and Giacobini-Zinner in 1959 and 1972 are examined. Brightness behavior of comets and the general level of solar activity in the eleven-year cycle appear to be statistically related. At present the responses of individual comets to solar events are not sufficiently well calibrated to permit using them as reliable interplanetary probes.     

Cryptographic Digital Communication

This paper reviews the fundamentals of cryptographic digital systems and defines and discusses the two basic types of ciphers. The remainder of this article examines the word and bit error rates in digital al communication systems with block or stream ciphers. Upper bounds and ensemble averages of the error rates are obtained for both ciphers. The effect of modulation type on the degradation in communication system performance caused by the addition of cryptography is analyzed. A comparison is made between block and stream ciphers with respect to their effects on degradation.     

Compensators for Bandpass Nonlinearities in Satellite Communications

The characteristics of optimum compensators for bandpass non-linearities are described. A predistortion compensator to reduce the nonlinear phase and envelope distortion at the output of a traveling-wave tube (TWT) is developed, and a possible implementation as a simple network of power law devices in cascade with the input to the TWT is given. The overall compensated characteristic of the TWT approximates that of a piecewise linear limiter with a small phase shift. A computer simulation shows that the compensated system yields 0.3 to 0.5-dB improvement in performance of a 2-phase coherent phase shift keying (CPSK) system over the uncompensated system.     

Effective Antenna Pattern of Scanning Radars

It is shown that weather radar signal averaging causes a broadened apparent pattern of the scanning radar antenna. The apparent pattern is obtained by convolving the original pattern with the averaging circuit impulse response. Echo displacement and pattern broadness are examined for square law, linear, and logarithmic detectors having exponential and finite time integrators.     

Dwelltime Minimization for Radar Target Detection in the Clear

Consider the design of a minimum dwelltime set of coherent, range-unambiguous pulse bursts that will provide a specified target detection performance in a clutter-free ("clear") range interval [Rmin,Rmax]. Practical procedures are presented here for finding these optimal waveform sets versus Rmax/Rmin, subject to a peak transmit power constraint. It is always possible to design a multiple-PRF clear mode that achieves the same effective use of energy as a single-PRF waveform with a 33 percent duty ratio. Slightly higher effective duty ratios can be achieved if the radar is capable of transmitting and processing two interleaved pulse bursts at the same PRF.     

Numerical simulation of the solar granulation

The solar granulation has been simulated by numerical solution of the multidimensional, time-dependent, nonlinear Navier-Stokes equations applied to the solar atmosphere. Granules may be explained as buoyantly rising bubbles created at the level where T = 8000 K, and which have collapsed into vortex rings. The calculation is in quantitative agreement with observations and has a number of implications for solar physics and convection theory.     

Effect of Sensor Errors on Automatic Gunfire Control

A formal approach is introduced toward mathematically relating errors in processed sensor data to their impact on error in gunfire of ground based, antiaircraft defense systems. An initial budget for sensor errors is formulated in terms of the accuracy requirements imposed upon the gunfire. The analysis is applicable to gun sites that are remotely located from the sensor as well as to colocated gun sites. Here, the radial components of sensor errors (along the sensor track line) are found to affect the target-miss distance of a remote gun by at least an order of magnitude more than their effect on the miss distance of a colocated gun. However, the effects of the traverse components of sensor errors (across the sensor track line) are found comparable in magnitude between remote and colocated guns.     

Open systems architecture for integrated RF electronics

The Integrated Sensor System (ISS) program is defining an Open System Architecture (OSA) for Radio Frequency (RF) electronics, which represent the largest portion of an advanced aircraft's avionics flyaway cost. An integrated architecture is used to reduce costs in a number of ways, including time-sharing, centralization of resources, and reduction of the number of unique module types. The OSA approach extends these cost reductions by simplifying technology insertion, using well-understood standards, and increasing use of commercial hardware and software. This paper describes interim results. The work was funded by the Open Systems Joint Task Force (OS-JTF)     

A robust exponential mixture detector applied to radar

Exponential mixture probability density functions (pdfs) are shown to be useful models of radar sea clutter. The variability of certain parameters leads to estimation error and degradation in the performance of detection algorithms derived from this model. Robust implementations are introduced by assuming that parameters are known within certain intervals and selecting values to prevent an excessive number of false alarms. An empirical study demonstrates an average 6-9 dB gain in comparison with a constant false-alarm rate (CFAR) processor