Vikram Sarabhai Space Centre

About: Vikram Sarabhai Space Centre is a facility organization based out in Thiruvananthapuram, India. It is known for research contribution in the topics: Aerosol & Ultimate tensile strength. The organization has 2092 authors who have published 3058 publications receiving 47975 citations. The organization is also known as: VSSC.

Simplified Active Array L-Band Radar for Atmospheric Wind Profiling: Initial Results

Abstract: A simple approach is presented to implement an active aperture radar with a constrained beam-forming network that is adequate enough to generate multiple beams for atmospheric wind profiling. In this approach, elements of the antenna array are fed directly by dedicated transceiver modules, which are realized with commercially available communication components, making them low cost. A passive 2D beam-forming network distributes the exciter output signal and feeds the transceivers with appropriate phase distribution to generate different beams. This configuration, which is a simplified active array, eliminates the feed loss and achieves the best signal-to-noise ratio (SNR), thereby increases range coverage. Consequently, this scheme allows for a smaller antenna size when compared to a conventional passive array system, for the given range performance, and makes the wind profiler compact and transportable. A 1280-MHz, 64-element simplified active array radar has been developed, successfully validated, and is being operated at Gadanki, a tropical station in south India. Measured winds are in good agreement with those obtained with a collocated GPS sonde technique. This paper presents the configuration and sample results of the system.

Hybrid Poly(hydroxy urethane)s: Folded-Sheet Morphology and Thermoreversible Adhesion

Abstract: Hybrid poly(hydroxy urethane)s (PHUs) are synthesized by copolymerizing aromatic/alicyclic cyclic carbonates with a polyether amine via addition polymerization. They result into polymers with an av...

Observational assessment of the potential of satellite‐based water vapor and thermal IR brightness temperatures in detecting semitransparent cirrus

Abstract: [1] Satellite observations of brightness temperature in the atmospheric window and water vapor bands are widely used for studying the regional/global distribution of semi-transparent cirrus (STC). The present study provides the first quantitative assessment of the lower limit of cloud optical depth (COD) of STC that can be detected using this method and the conditions under which these observations are reliable, by comparing the STC information derived from the Very High Resolution Radiometer (VHRR) onboard the Indian geostationary satellite KALPANA-1 over the tropical station Gadanki (13.5°N, 79.2°E) with cirrus COD obtained from collocated Lidar observations for 12 nights during different seasons under contrasting cloud conditions. Satellite-derived STC amount is found to be highly reliable when COD > 0.02 and is an underestimate when it decreases below 0.02, especially when they appear as broken clusters. However, in most of the cases, satellite could detect very thin STC with COD < 0.02 when they are widespread.

Fatigue crack growth of AA2219 under different aging conditions

Abstract: The fatigue crack growth of commercial AA2219 has been examined under different aging treatments, namely, naturally aged (NA), under aged (UA), peak aged (PA) and over aged (OA) conditions. From the near threshold stress intensity range (Δ K NTH ), the alloy in the NA condition is found to have the highest resistance to fatigue crack initiation. The crack growth rate increases and the near threshold stress intensity range decreases with advancing aging. This observation is found to be consistent with lower levels of crack closure and decreasing levels of tortuosity in crack path for PA and OA tempers. The inhomogeneous transcrystalline slip in the UA condition results in the slower crack growth at low stress intensity range (Δ K ). The fracture morphology changes from crystallographic facets near the threshold region to clearly developed ductile striations in the Paris power-law regime to microvoid coalescence in the high Δ K regions.