Defence Research Agency

About: Defence Research Agency is a based out in . It is known for research contribution in the topics: Synthetic aperture radar & Radar. The organization has 1211 authors who have published 1109 publications receiving 31542 citations.

On efficient characterization of radar targets with scatterer sets for target recognition using commercial ray tracing software

Abstract: The model-based radar target recognition requires the ability to simulate target signatures with adequate accuracy and computational speed. This paper proposes an entirely novel approach to utilizing readily available ray tracing software in the target characterization. The objective of the proposed approach is to give the target a compact description, from which arbitrary radar response can be simulated with efficiency. Certain essential computational aspects, such as ray density reduction and frequency-independency, are discussed. The simulated radar response is compared with a measurement, covering the case of a single frequency, high range resolution profiles, and inverse synthetic aperture radar images.

Transverse-mode selection in apertured super-Gaussian resonators: an experimental and numerical investigation for a pulsed CO(2) Doppler lidar transmitter.

Abstract: A representative prototype of a high-energy, long-pulse, and narrow-bandwidth pulsed CO2 laser suitable for a spaceborne Doppler wind lidar application has been developed. We obtained 10 J of output energy at greater than 8% efficiency in long, narrow-bandwidth, single-longitudinal, and transverse-mode pulses. We used a positive branch unstable resonator with a fourth-order super-Gaussian mirror as the output coupler. Experiments were carried out to assess the effect of intracavity hard apertures of different diameters that induce diffractive perturbation of the theoretical field and reduce the transverse-mode selectivity of the cavity. An upper limit to the choice of the mirror soft radius has been found, which allows optimization of the trade-off between laser efficiency and beam quality. We determined experimentally that a value of 0.75–0.8 for the ratio between the exp(-1) diameter of the beam intensity and the laser clear aperture gave a single-transverse-mode operation without significant loss of efficiency.

The application of the Graham and Walles creep equation to aeroengine superalloys

Abstract: The paper briefly discusses the charcteristics of creep deformation and the requirements of any creep equation developed to quantify this behavior. It is shown how the Graham and Walles methodology (1)† fulfils the identified objectives and how the equations have been applied to simple and complex variable loading situations.By reference to an appropriate blade alloy it will be shown that the approach can be extended to produce deformation maps and the results will be compared with theoretical creep models such as dislocation shearing of precipitate particles.Finally it is shown how the Graham and Walles model has been applied to single crystal materials to predict creep in randomly oriented crystals.