The INFRARED SPACE OBSERVATORY (ISO)

The INFRARED SPACE OBSERVATORY (ISO), a project of the European Space Agency (ESA), will make various astronomical observations in the wavelength range of 2 to 200 μm. Two-thirds of its observing time will be available to guest observers via the traditional route of proposal submission. ISO will be launched in 1995 by an Ariane 4 from Kourou (Guyana) and be brought into a very elongated orbit with a 24hr period of which 16 hr can be used for astronomical observations. The payload module is essentially a large cryostat with a tank that will be filled with over 2000 litres of superfluid helium to keep the instruments cold (2 to 4 K) during an expected lifetime of 18 months. Inside the dewar, there is a Ritchey-Chretien telescope with a primary mirror of diameter 60cm. Four instruments, each provided by a different PI consortium, share the ISO focal plane. These instruments are : a photometer, a camera and two spectrometers — one for the wavelength range 2–45 μm and the other for 45–180 μm.     

SIGMA observations of two new hard X-ray and soft gamma-ray transients: GX 354-0 and Nova Persei

We report the first detection of two soft gamma ray transients GX 354-0 and Nova Persei (GRO J0422+32) by the coded-mask telescope SIGMA. Only preliminary results are presented with regard to Nova Persei while special emphasis is given to the data on GX 354-0 which has been monitored during the 1992 February–April survey of the Galactic Center. GX 354-0 underwent two flares of about two week duration and its average spectrum is well described by a thermal Bremsstrahlung model or a broken power law whereas the Nova Persei spectrum seems to be similar to the one observed for GRS 1124-684 in Musca.     

Antideuterons as an indirect dark matter signature: Si(Li) detector development and a GAPS balloon mission

The General AntiParticle Spectrometer (GAPS) is a novel approach for indirect dark matter searches that exploits cosmic antideuterons. GAPS complements existing and planned direct dark matter searches as well as other indirect techniques, probing a different and unique region of parameter space in a variety of proposed dark matter models. The GAPS method involves capturing antiparticles into a target material with the subsequent formation of an excited exotic atom. The exotic atom decays with the emission of atomic X-rays and pions from the nuclear annihilation, which uniquely identifies the captured antiparticle. This technique has been verified through the accelerator testing at KEK in 2004 and 2005. The prototype flight is scheduled from Hokkaido, Japan in 2011, preparatory for a long duration balloon flight from the Antarctic in 2014.     

DORIS geodesy: A dynamic determination of geocentre location

Geoscience Australia contributed a multi-satellite, multi-year weekly time series to the International DORIS Service combined submission for the construction of International Terrestrial Reference Frame 2008 (ITRF2008). This contributing solution was extended to a study of the capability of DORIS to dynamically estimate the variation in the geocentre location. Two solutions, comprising different constraint configurations of the tracking network, were undertaken. The respective DORIS satellite orbit solutions (SPOT-2, SPOT-4, SPOT-5 and Envisat) were verified and validated by comparison with those produced at the Goddard Space Flight Center (GSFC), DORIS Analysis Centre, for computational consistency and standards. In addition, in the case of Envisat, the trajectories from the GA determined SLR and DORIS orbits were compared. The results for weekly dynamic geocentre estimates from the two constraint configurations were benchmarked against the geometric geocentre estimates from the IDS-2 combined solution. This established that DORIS is capable of determining the dynamic geocentre variation by estimating the degree one spherical harmonic coefficients of the Earth’s gravity potential. It was established that constrained configurations produced similar results for the geocentre location and consequently similar annual amplitudes. For the minimally constrained configuration Greenbelt–Kitab, the mean of the uncertainties of the geocentre location were 2.3, 2.3 and 7.6 mm and RMS of the mean uncertainties were 1.9, 1.2 and 3.5 mm for the X, Y and Z components, respectively. For GA_IDS-2_Datum constrained configuration, the mean of the uncertainties of the geocentre location were 1.7, 1.7 and 6.2 mm and RMS of the mean uncertainties were 0.9, 0.7 and 2.9 mm for the X, Y and Z components, respectively. The mean of the differences of the two DORIS dynamic geocentre solutions with respect to the IDS-2 combination were 1.6, 4.0 and 5.1 mm with an RMS of the mean 21.2, 14.0 and 31.5 mm for the Greenbelt–Kitab configuration and 4.1, 3.9 and 4.3 mm with an RMS 8.1, 9.0 and 28.6 mm for the GA_IDS-2_Datum constraint configuration. The annual amplitudes for each component were estimated to be 5.3, 10.8 and 11.0 mm for the Greenbelt–Kitab configuration and 5.3, 9.3 and 9.4 mm for the GA_IDS-2_Datum constraint configuration. The two DORIS determined dynamic geocentre solutions were compared to the SLR determined dynamic solution (which was determined from the same process of the GA contribution to the ITRF2008 ILRS combination) gave mean differences of 3.3, −4.7 and 2.5 mm with an RMS of 20.7, 17.5 and 28.0 mm for the X, Y and Z components, respectively for the Greenbelt–Kitab configuration and 1.1, −5.4 and 4.4 mm with an RMS of 9.7, 13.3 and 24.9 mm for the GA_IDS-2_Datum configuration. The larger variability is reflected in the respective amplitudes. As a comparison, the annual amplitudes of the SLR determined dynamic geocentre are 0.9, 1.0 and 6.8 mm in the X, Y and Z components. The results from this study indicate that there is potential to achieve precise dynamically determined geocentre from DORIS.     

Structures for radar detection in compound Gaussian clutter

The problem of coherent radar target detection in a background of non-Gaussian clutter modeled by a compound Gaussian distribution is studied here. We show how the likelihood ratio may be recast into an estimator-correlator form that shows that an essential feature of the optimal detector is to compute an optimum estimate of the reciprocal of the unknown random local power level. We then proceed to show that the optimal detector may be recast into yet another form, namely a matched filter compared with a data-dependent threshold. With these reformulations of the optimal detector, the problem of obtaining suboptimal detectors may be systematically studied by either approximating the likelihood ratio directly, utilizing a suboptimal estimate in the estimator-correlator structure or utilizing a suboptimal function to model the data-dependent threshold in the matched filter interpretation. Each of these approaches is studied to obtain suboptimal detectors. The results indicate that for processing small numbers of pulses, a suboptimal detector that utilizes information about the nature of the non-Gaussian clutter can be implemented to obtain quasi-optimal performance. As the number of pulses to be processed increases, a suboptimal detector that does not require information about the specific nature of the non-Gaussian clutter may be implemented to obtain quasi-optimal performance     

Analysis and results of the 1995 Yuma ground penetration SARmeasurements

In July and October 1995, a large-scale airborne SAR experiment was conducted in the Yuma Proving Ground, Yuma, Arizona, to investigate ground penetration radar phenomenology and buried target detection. This paper describes the Yuma experiment and measurement results for many tactical, utility, and environmental targets deployed in the test     

Test System Impact on System Availability

The specifications are presented for an imperfect automatic test system (ATS) (test frequency distribution, reliability, false alarm rate, nondetection rate) in order to account for the availability, readiness, mean time between unscheduled repairs (MTBUR), reliability, and maintenance of the system subject to monitoring and test. A time-dependent Markov model is presented, and applied in three cases, with examples of numerical results provided for preventive maintenance decisions, design of an automatic test system, buffer testing in computers, and data communications.     

Voyager 2 Observations of Corotating Interaction Regions (CIRs) in the Outer Heliosphere

We review observations from Voyager 2 of CIRs and merged CIRs in the outer heliosphere. The rather simple characteristics of the CIR-associated changes in plasma, magnetic field, and particles become more complex as observations are made at greater and greater distances. Pickup ions from charge exchange undoubtedly play an important role in the structure, but the full details are not yet understood. This revised version was published online in August 2006 with corrections to the Cover Date.     

Magnetospheric Models and Trajectory Computations

The calculation of particle trajectories in the Earth's magnetic field has been a subject of interest since the time of Störmer. The fundamental problem is that the trajectory-tracing process involves using mathematical equations that have `no solution in closed form'. This difficulty has forced researchers to use the `brute force' technique of numerical integration of many individual trajectories to ascertain the behavior of trajectory families or groups. As the power of computers has improved over the decades, the numerical integration procedure has grown more tractable and while the problem is still formidable, thousands of trajectories can be computed without the expenditure of excessive resources. As particle trajectories are computed and the characteristics analyzed we can determine the cutoff rigidity of a specific location and viewing direction and direction and deduce the direction in space of various cosmic ray anisotropies. Unfortunately, cutoff rigidities are not simple parameters due to the chaotic behavior of the cosmic-ray trajectories in the cosmic ray penumbral region. As the computational problem becomes more manageable, there is still the issue of the accuracy of the magnetic field models. Over the decades, magnetic field models of increasing complexity have been developed and utilized. The accuracy of trajectory calculations employing contemporary magnetic field models is sufficient that cosmic ray experiments can be designed on the basis of trajectory calculations. However, the Earth's magnetosphere is dynamic and the most widely used magnetospheric models currently available are static. This means that the greatest uncertainly in the application of charged particle trajectories occurs at low energies.     

A method for representing the thermodynamic and thermophysical functions in simulation of powerplant processes

A method for representing thermodynamic and thermophysical functions is presented; the functions make it possible to simulate thermal and gasodynamic processes in powerplants that use different individual substances or their mixtures as a working fluid. The method also involves consideration of real gas properties.