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.

A statistical description of polarimetric and interferometric synthetic aperture radar data

Abstract: This paper provides a nearly complete analysis of the key distributions encountered in single- and multi-look polarimetric synthetic aperture radar data under the bivariate Gaussian and K -distribution models. It contains new analytic results on the moments of the amplitude and phase difference in single look data and on the moments of the amplitude in multi-look data. As yet no analytic results for the moments of multi-look phase difference have been found, except in limiting cases. The maximum likelihood estimators of the covariance matrix elements of two jointly Gaussian channels are derived, together with their asymptotic variances. The problems in extending this analysis to the bivariate K distribution are also discussed.

Knowledge elicitation using discourse analysis

Abstract: This paper is concerned with the use of discourse analysis and observation to elicit expert knowledge. In particular, we describe the use of these techniques to acquire knowledge about expert problem solving in an information provision environment. Our method of analysis has been to make audio-recordings of real-life information interactions between users (the clients) and human intermediaries (the experts) in document retrieval situations. These tapes have then been transcribed and analysed utterance-by-utterance in the following ways: assigning utterances to one of the prespecified functional categories; identifying the specific purposes of each utterance; determining the knowledge required to perform each utterance; grouping utterances into functional and focus-based sequences. The long-term goal of the project is to develop an intelligent document retrieval system based on a distributed expert, blackboard architecture.

Novel techniques for high-capacity 60-GHz fiber-radio transmission systems

Abstract: A broad-band 60-GHz fiber-radio transmission experiment has been performed using a combination of novel techniques. The 60-GHz carrier signal was generated using a master/slave (M/S) distributed-feedback (DFB) laser configuration, which gave high purity and high power with very wide frequency tunability. The data path was separated in the wavelength domain from the carrier path so that a remote upconversion scheme could be used to provide a fully transparent link. An electroabsorption modulator (EAM) was used as a full duplex transceiver so that bidirectional optical transmission could be implemented without the need for a laser at the remote site. Transmission of a 120-Mb/s QPSK signal over a fiber span of 13 km and a radio path of 5 m was demonstrated. Furthermore, the downstream optical signal contained the 120-Mb/s QPSK signal multiplexed with 20 channels of TV. The upstream optical signal consisted of 120-Mb/s QPSK data only. Good error performance was simultaneously achieved in both directions.