Environment and Radar Operation Simulator

The environment and radar operation simulator (EROS) is a hardware system whose function is to produce realistic synthetic radar backscatter, incorporating both target and clutter. The simulator is electrically connected to a subject radar and responds in real time to the radar's antenna scan angle by producing the correct composite video signal.     

The variability of the sun's ultraviolet radiation

The intensity of continua and emission lines which form the solar UV spectrum below 2100 Å is variable. Continua and emission lines originating from different layers in the solar atmosphere show a different degree of variability. Coronal emission lines at short wavelengths are much more variable than continua at longer wavelengths which originate in lower layers of the solar atmosphere. Typical time-scales of solar UV variability are minutes (flare induced), days (birth of active regions), 27 days (solar rotation), 11 years (solar cycle) and perhaps centuries, caused by long-term changes of the solar activity. UV intensity variations have been determined by either absolute irradiance measurements or by contrast measurements of plages vs. the quiet sun. Plages are the main contributor to the solar UV variability. Typical values for the solar UV variability over a solar cycle are: <1% at wavelengths longer than 2100 Å, 8% at 2080 Å (continuum), 20% at 1900 Å (continuum), 70% at H Lyα, 200% in certain emission lines 1200 < λ < 1800 Å and more than a factor of 4 in coronal lines λ < 1000 Å. Plage models predict the variable component of the solar UV radiation within ±50%. Absolute fluxes are known within ±30%. Several efforts are underway to monitor the solar UV irradiance with a precision better than a few percent over a solar activity cycle.     

Responses of the upper middle atmosphere (60–110 km) to the stratwarms of the four pre-map winters (1978/9–1981/2)

The global developments of the four stratospheric events (～20–50 km) are described, using balloon, satellite and rocket data. Winds data for heights of 60–95 km, derived from L.F. drift (52°N, 15°E; Europe) and M.F. radar (52°N, 107°W; Canada), are then compared with the stratospheric data. There is clear evidence that the preliminary planetary waves often penetrate strongly to ～90 km, and that mean wind reversals also occur. However, there are dramatic differences between European and Canadian mesospheric responses.     

The giant planets and their satellites: Report on the Cospar Symposium,Ottawa, Canada,May 18–21, 1982

A $\text{Symposium on the Giant Planets and Their Satellites}$ was presented in conjunction with the Twenty-fourth Plenary Meeting of the Committee on Space Research. This paper summarizes the talks presented and places the remaining papers of this volume in context.     

Heavy ion action on yeast cells: inhibition of ribosomal-RNA synthesis, loss of colony forming ability and induction of mutants.

The action of heavy ions (Ar to U) accelerated to specific energies up to about 10 MeV/u (u=atomic mass unit) on different functions of yeast cells was studied. Ribosomal-RNA synthesis is inhibited according to a single-hit mechanism. Inactivation cross-sections were linearly related to the ratio of the squares of the effective charge Z* and the velocity of the ions. It is concluded from the analysis that the range of the most energetic delta-electrons is larger than previously assumed. There is no such dependence for survival and induction of mutants. In both cases cross-sections increase with the ion's specific-energy indicating an important contribution of long-range delta-electrons. The analysis shows that diploid yeast is not killed by a single-hit mechanism even by very heavy ions if the track width is too small. The relative importance of the penumbral region is even more pronounced with the more sensitive strains.     

Leading Edge Estimation Errors

The leading edge estimator (LEE) of a pulse signal is defined as the instant at which a filtered version of the received noisy signal passes a preset threshold. A rigorous analysis for a rectangular pulse model of the signal results in an exact probability density function for the LEE, valid within the time interval of the leading edge of the filtered pulse. Possible occurrence of the threshold crossing outside of this interval is considered to be an anomalous estimate, since it leads to a gross error in comparison with the regular cases. It is found that the density function of the LEE error is asymmetrical and therefore biased, that the probability PA of anomalous estimation increases with the filter bandwidth, thus setting a well definable limit to the latter and that, for prespecified PA, the minimum bias and variance are proportional, respectively, to R-1 and R-2, minima being obtained by allowing for the largest bandwidth compatible with PA. On the other hand, for given bandwidth the variance decreases only as R-1. Here R is the signal-to-noise energy ratio. Results are presented in form of parameterized graphs.     

The Resolution Performance of Range Estimators

The theoretical basis and methods of implementation of a moment algorithm for the range separation estimation of two closely spaced point targets are presented. Moment estimation and noise filtering techniques introduced here result in a considerable improvement over Baum's algorithm. The error bounds are established and it is shown that the spectral moment estimator exhibits optimum (zero bias, minimum variance) performance when the target separation normalized to the standard deviation of the Gaussian pulse is 2?1.5. Monte Carlo simulation is performed to verify the approximations made and to demonstrate the feasibility of the working models.     

The Magellan project

Magellan is one of the future space projects being studied by the European Space Agency. The aim is to provide high resolution (λ/Δλ ≥ 2.5 × 10⁴) spectra in the far and extreme UV (between 500 and 1550 Å) of faint galactic and extragalactic objects (V ≤ 16^m). The instrument consists of a mechanical collimator, a concave holographic grating and a bidimensional photon-counting detector. A low resolution mode (λ/Δλ ≥ 10³) will provide spectra of objects as faint as 18^m.5. Magellan is planned as an observatory, operated in real time, and allowing interaction with the observer.     

Dissipation of temperature perturbations in the middle atmosphere

It is often observed that the stratospheric and mesospheric temperature structure undergoes transient disturbances from its averaged steady-state behavior. The causes may be traceable to gravity waves, planetary waves, solar proton and relativistic electron precipitation, etc. We examine the theoretical time behavior of the atmospheric temperature following the cessation of such heating phenomena as it relaxes toward its quiescent steady-state value. We also study the time-dependent response during a model stratospheric-warming/mesospheric-cooling event. In particular, we investigate the roles of eddy heat conduction, non-LTE cooling in the 15μm CO₂ band, and an ambient vertical wind, and their relative importance as they depend upon altitude and time, in modifying temperature changes in this region.     

Comet nucleus sample return: Plans and capabilities

ROSETTA — the Comet Nucleus Sample Return mission — is one of the four Cornerstone missions to which ESA has committed itself in its approved Long-Term Programme Horizon 2000. The mission is currently being studied in collaboration with NASA. The comet-nucleus samples that ROSETTA is to provide will allow us to study some of the most primitive material in the solar system and the physical and chemical processes that marked the beginning of the system 4.6 billion years ago. For ESA, ROSETTA is a new type of mission: one which will return a sample at cryogenic temperature, and where as much effort has to be spent on preparing the laboratory analysis on-ground as has to be invested in preparing the space segment with the sample acquisition and in situ documentation. As part of the preparation for this mission, ESA is now starting to consider Planetary Protection issues.