Tracking Performance of a Monopulse Radar in the Presence of Multiple Targets

The equations derived by A. J. Rainal for the probability density function of the angle error output of a monopulse radar excited by a Gaussian signal and Gaussian thermal noise are generalized to include the presence of multiple targets. The examples given demonstrate the radar's behavior for various combinations of target and noise parameters.     

Airglow in the Visible and Infrared Spectral Ranges of the Disturbed Upper Atmosphere under Conditions of High-Velocity Plasma Jet Injection: I. Experimental data

The measurements of infrared emission from an artificial structure, which was generated during the Fluxus experiment with plasma jet injection into the atmosphere, are obtained and discussed for the first time. Additional experimental data on the airglow in the visible spectral band of the disturbed region of the atmosphere are presented. A generalized analysis of the data is given.     

Conjugate features of magnetospheric electron dynamics observed at balloon altitudes

Analysis of recent observations (from balloons, spacecraft, and surface observatories) demonstrate regional, shell, and nearpoint conjugacy at L ～ 7 during precipitative events which were characterized by local acceleration as well as release of gradient-drifted electrons injected during substorms. A number of new features of magnetospheric dynamics relating to substorm development and sudden-commencement effects, have been brought to light which, though poorly understood at present, may prove of considerable importance and are worthy of further investigation.

1. During the initial period of instability in substorm evolution, preceding the slower magnetotail convective injection, precipitation of waves of electrons in rapid polewards motion exhibit L-shell conjugacy near midnight.
2. Transient, large scale expansions of the magnetospheric electron population accompanied by temporally imbedded substorms display large scale regional conjugacy and are simultaneously observed as similarly transient intensity dropouts at balloon altitudes.
3. Precipitation from gradient-drifting electrons in the dayside magnetosphere exhibits near point-conjugacy, at least down to the order of 50 km and quite probably less.

Similarly tight conjugacy applies to the release of electrons showing a specific local response to sudden commencements.

1. Analysis of the approach to and attainment of spectral equilibrium in the precipitation observed from drifting electrons may provide information about either, or both, the source spectrum at injection and the process of local release.
2. The specific precipitation effect sometimes observed at the time of an SC remains a rather puzzling feature, although it seems clear now that the acceleration and/or release process responsible is of a highly local nature and works selectively at small pitch angles well within the magnetospheric boundary. Coupling of the interplanetary shock with the magnetosphere must be an important aspect, but the details are not clear as yet.
3. On at least one occasion, a large part (perhaps all) of the magnetospheric electron population varied in a nearly synchronous manner in response to solar wind induced distortions during the variable compressive phase of a sudden commencement geomagnetic storm.

In the ongoing effort to identify and understand acceleration and release mechanisms involved in magnetospheric dynamics, balloon-borne experiments will continue to be useful, providing essential information presently unattainable by other means.     

Transforming solar system exploration: The origins of the Discovery Program, 1989–1993

The Discovery Program is a rarity in the history of NASA solar system exploration: a reform program that has survived and continued to be influential. This article examines its emergence between 1989 and 1993, largely as the result of the intervention of two people: Stamatios “Tom” Krimigis of the Johns Hopkins University Applied Physics Laboratory (APL), and Wesley Huntress of NASA, who was Division Director of Solar System Exploration 1990–92 and the Associate Administrator for Space Science 1992–98. Krimigis drew on his leadership experience in the space physics community and his knowledge of its Explorer program to propose that it was possible to create new missions to the inner solar system for a fraction of the existing costs. He continued to push that idea for the next two years, but it took the influence of Huntress at NASA Headquarters to push it on to the agenda. Huntress explicitly decided to use APL to force change on the Jet Propulsion Laboratory and the planetary science community. He succeeded in moving the JPL Mars Pathfinder and APL Near Earth Asteroid Rendezvous (NEAR) mission proposals forward as the opening missions for Discovery. But it took Krimigis's political skill and access to Sen. Barbara Mikulski in 1993 to get the NEAR into the NASA budget, thereby likely ensuring that Discovery would not become another one-mission program.     

Sources of Interference in Spatial Long-Term Memory Retrieval

Three experiments are reported that used an interference paradigm to test the extent to which perceptual orientation to a task environment interfered with retrieval from long-term spatial memory. Visual and spatial sources of interference were tested. The findings were consistent with a spatial locus of interference and showed that orientation to the task environment disrupted the accessibility of relative direction under two retrieval conditions: when the imagined viewpoint was 180 degrees misaligned with the actual viewpoint and when the actual body location was anterior to the imagined body location. While the former finding replicates previous reports of interference in perspective-taking tasks, the latter finding is new and difficult for current models of spatial long-term memory retrieval to explain. More research is needed to articulate further the constraints that perceptual orientation to the task environment place on spatial retrieval and their implications for models of spatial memory.     

The team ROC curve in a binary hypothesis testing environment

We consider the distributed detection problem, in which a set of decision makers (DMs) receive observations of the environment and transmit finite-valued messages to other DMs according to prespecified communication protocols. A designated primary DM makes the find decision on one out of two alternative hypotheses. All DMs make decisions, in order to maximize a measure of organizational performance. We discuss three different types of decision rules (deterministic, independent randomization, and dependent randomization), and their implications on the organizational performance. Each DM is described by its individual receiver operating characteristic (ROC) curve, which is concave. We determine that concavity is not guaranteed for the case of the ROC curve of a team of DMs, even if the decision rules are perfectly continuous and if the individual ROC curves are strictly concave and smooth unless dependent randomization is allowed     

Introduction

Space Science Reviews -     

The Effect of Pulse Shape and Duty Cycle on Laser Binary Communication Systems

The result of an investigation of the effects of pulse shape and duty cycle on the probability of error are presented for a pulse-gated binary modulation (PGBM) laser communication system when the background irradiance has the important Lorentzian spectral shape.