On the breakdown of wave fronts of characteristics in an ideal dissociating gas

Using the method of characteristics, the problem of breaking or non-breaking of waves is studied in a plane cylindrically or spherically symmetric flow of an ideal dissociating gas. It is investigated as to how the effects of dissociation and that of the wave front curvature influence the breaking or non-breaking of waves. In a symmetrical converging gas motion a remarkable difference between the behaviours of cylindrical and spherical waves is discovered.     

Potential of IRNSS/NavIC L5 signals for ionospheric studies

Indian Space Research Organization (ISRO) has developed an indigenous system named Indian Regional Navigation Satellite System (IRNSS) or NavIC (Navigation with Indian Constellation), that consists of 7 satellites and transmits navigation signal in L and S bands. ISRO, for validation of the system, has installed many IGS (IRNSS/GPS/SBAS) receivers scattered over the Indian region. Using preliminary data from two geographically widely separated stations over India, this paper presents the results on studies on parameters of IRNSS signal quality and discusses how these parameters may be used to study the ionospheric behavior over the Indian region. The results show the importance and advantages of using IRNSS data for such studies.     

An Artificial Neural Network based approach for estimation of rain intensity from spectral moments of a Doppler Weather Radar

By using a Doppler Weather Radar (DWR) at Shriharikota (13.66°N & 80.23°E), an Artificial Neural Network (ANN) based technique is proposed to improve the accuracy of rain intensity estimation. Three spectral moments of a Doppler spectra are utilized as an input data to an ANN. Rain intensity, as measured by the tipping bucket rain gauges around the DWR station, are considered as a target values for the given inputs. Rain intensity as estimated by the developed ANN model is validated by the rain gauges measurements. With the help of a developed technique, reasonable improvement in the estimation of rain intensity is observed. By using the developed technique, root mean square error and bias are reduced in the range of 34–18% and 17–3% respectively, compared to Z–R approach.     

Occurrence of equatorial plasma bubbles over Kolhapur

This paper reports the nightglow observations of OI 630.0 nm emissions, made by using all sky imager operating at low latitude station Kolhapur (16.8°N, 74.2°E and dip lat. 10.6°N) during high sunspot number years of 24th solar cycle. The images are analyzed to study the nocturnal, seasonal and solar activity dependence occurrence of plasma bubbles. We observed EPBs in images regularly during a limited period 19:30 to 02:30 LT and reach maximum probability of occurrence at 22:30 LT. The observation pattern of EPBs shows nearly no occurrence during the month of May and it maximizes during the period October–April. The equinox and solstice seasonal variations in the occurrence of plasma bubbles show nearly equal and large differences, respectively, between years of 2010–11 and 2011–12.     

Evolution of periodic orbits near the Lagrangian point L2

A study of the evolution of the periodic and the quasi-periodic orbits near the Lagrangian point L₂, which is located to the right of the smaller primary on the line joining the primaries and whose distance from the more massive primary is greater than the distance between the primaries, in the framework of restricted three-body problem for the Sun–Jupiter, Earth–Moon (relatively large mass ratio) and Saturn–Titan (relatively small mass ratio) systems is made. Two families of periodic orbits around the smaller primary are identified using the Poincaré surface of section method – family I (initially elliptical, gradually becomes egg-shaped with the increase in the Jacobi constant C and elongated towards the more massive primary) and family II (initially egg-shaped orbits elongated towards L₂ and gradually becomes elliptical with the increase in C). The family I in the Sun–Jupiter and Saturn–Titan systems contains two separatrix caused by third-order and fourth-order resonances, while the Earth–Moon system has only one separatrix which is caused by third-order resonances. Also in the Sun–Jupiter and the Saturn–Titan systems, family I merge with family II, around Jacobian constant 3.0393 and 3.0163, respectively, while in the Earth–Moon system, family II evolves separately from two different branches. The two branches merge at C = 3.184515. In the Earth–Moon system, the family II contains a separatrix due to third-order resonances which is absent in the other two systems.     

Venus atmospheric circulation: Observations and implications of the thermal structure

Continued analysis of Pioneer Venus imaging and polarimetry data indicates that the average cloud-top level circulation is mainly zonal (east to west) with a small meridional component. Presence of planetary scale waves and a possible sun-related component are evident in the data. If the tracked features refer to the same vertical level, then some variability of the circulation would have to be present to account for the Pioneer and Mariner 10 cloud-tracking results. However, the implied balanced flow from the observed thermal structure analysis strongly suggests that at least some of the variations in these observations is due to apparent cloud-top variations and that the circulation itself is relatively stable.Direct cyclostrophic calculations based on the observed thermal structure of the atmosphere yield a balanced zonal circulation with distinct mid-latitude jets (peak velocities about 110–120 ms^?1) located between 50 and 40 mb in each hemisphere of the planet near 45° latitude. The calculations which extend to about 40 km altitude from 80 km above the surface agree well with the observed entry probe zonal components and indicate breakdown of the balance condition near the upper and lower boundaries at low latitudes.The balanced flow results are consistent with the Mariner 10 and Pioneer cloud tracked estimates of the zonal circulation provided the effective altitude of the tracked features is slightly different at different observation periods. The features in the Pioneer Venus data would then lie on a sloping surface that extends from about 68 km (40 mb) at low latitudes to about 75 km (10 mb) in mid-latitudes. The polarization features would occur on a roughly parallel surface that is 1–2 km above the effective cloud-height surface, and Mariner 10 features would have effective altitudes somewhat lower than the Pioneer ultraviolet features. A slight asymmetry is evident in the balanced zonal circulation arising out of an asymmetry in the thermal field.Finally, the solenoids formed by intersecting isobaric and isosteric (constant specific volume) surfaces deduced from the Pioneer Venus radio occultation data show distinct evidence of a direct meridional circulation that may be important in sustaining the Venus atmospheric circulation.     

Aeronautical use of semiconductor lasers for short optical pulses

In this paper, we investigate the feasible schemes to generate periodic optical pulses of width between several picoseconds (ps) and tens ps. Gain-switched semiconductor laser diodes are shown to be more suitable for avionics applications than mode-locked laser diodes. In the experiment, we use a low-cost Fabry-Perot laser diode to generate short optical pulse streams. A simple optical injection-locking scheme is then used to reduce the timing jitter and frequency chirp in such laser diodes, which in turn can improve the transmission performance of the generated optical pulses. It is expected that the use of gain-switched semiconductor lasers can meet the requirement of high-speed airborne communication networks or ground supporting systems at airports. Moreover, we discuss the possibility of using the pulsed semiconductor lasers to generate millimetre-wave (mm-wave) signals for future applications to airborne high-resolution, mm-wave radars.     

The Scanning Sky Monitor (SSM) on ASTROSAT

The Scanning Sky Monitor is one of the experiments onboard the ASTROSAT, an Indian multiwavelength astronomy satellite mission. This experiment will detect and monitor X-ray transients in the energy band 2–10 keV. It is similar in design to the ASM on RXTE. It consists of position-sensitive proportional counters with one-dimensional mask. We describe the configuration of the experiment. We also discuss some of the results obtained using a detector which has already been fabricated and tested in our laboratory.     

Avionics data buses: an overview

An overview of military avionics data buses and their applications, with the emphasis on optical fiber networking techniques. The evolution of military avionics data buses is discussed. The development trend actually reflects an increasing demand on such data buses, which requires the change from low-speed to high-speed transmissions, from single-rate to dual-rate operations, and from centralized control to distributed control. Recent progress in military avionics networks is described.     

India's EO infrastructure for disaster reduction: Lessons and perspectives

India has established a ‘critical mass’ in terms of EO infrastructure for disaster management. Starting from IRS 1A in 1980s to the most recent CARTOSAT-2, India's EO series of satellites are moving away from the generic to thematic constellations. The series of RESOURCESAT, CARTOSAT, OCEANSAT and forthcoming Radar Imaging Satellite (RISAT) satellites exemplifies the thematic characters of the EO missions. These thematic constellations, characterized with multi-platform, multi-resolution and multi-parameter EO missions, are important assets for disaster reduction. In the more specific term, these constellations in conjunction with contemporary EO missions address the critical observational gaps in terms of capturing the catastrophic events, phenomena or their attributes on real/near real time basis with appropriate spatial and temporal attributes.Using conjunctively the data primarily emanating these thematic constellations and all weather radar data from aerial platform and also from RADARSAT as gap-fillers has been a part of India's EO strategy for disaster management. The infrastructure has been addressing the observational needs in disaster management. The high resolution imaging better than one-meter spatial resolution and also Digital Elevation Models (DEM) emanating from Cartosat series are providing valuable inputs to characterize geo-physical terrain vulnerability. Radar Imaging Satellite, with all weather capability missions, is being configured for disaster management. At present, the current Indian EO satellites cover the whole world every 40 h (with different resolutions and swaths), and the efforts are towards making it better than 24 h. The efforts are on to configure RESOURCESAT 3 with wider swath of 740 km with 23 m spatial resolution and also to have AWiFS type of capability at geo-platform to improve the observational frequencies for disaster monitoring.India's EO infrastructure has responded comprehensively to all the natural disasters the country has faced in the recent times. As a member of International Charter on Space and Major Disasters, India has also been instrumental in promoting the related UN initiatives viz., RESAP of UN ESCAP, SPIDER of UN OOSA, Sentinel Asia of JAXA initiative and also of GEOSS initiative. The paper intends to illustrate India's EO strategy for disaster reduction.