Future Satellite Payloads Research Articles

Classification of satellite-based radio frequency transient recordings using sparse approximations over learned dictionaries

Ongoing research at Los Alamos National Laboratory studies the Earth’s radio frequency (RF) background utilizing satellite-based RF observations of terrestrial lightning. Such impulsive events occur in the presence of additive noise and structured clutter and appear as broadband nonlinear chirps at a receiver on-orbit due to ionospheric dispersion. The Fast On-orbit Recording of Transient Events (FORTE) satellite provided a rich RF lightning database. Application of modern pattern recognition techniques to this database may further lightning research and potentially improve event discrimination capabilities for future satellite payloads. We extend two established dictionary learning algorithms, K-SVD and Hebbian, for use in classification of satellite RF data. Both algorithms allow us to learn features without relying on analytical constraints or additional knowledge about the expected signal characteristics. We use a pursuit search over the learned dictionaries to generate sparse classification features and discuss performance in terms of event classification using a nearest subspace classifier. We show a use of the two dictionary types in a mixed implementation to showcase algorithm distinctions in extracting discriminative information. We use principal component analysis to analyze and compare the learned dictionary spaces to the real data space, and we discuss some aspects of computational complexity and implementation.

An optical link for microwave clock distribution using optical carrier suppression and DC drift compensation

AbstractBias electrode DC drift of LiNbO3 optical modulators becomes a critical problem when these devices operate over a long time period. This article presents a novel system of DC drift compensation for optical microwave transmissions using optical carrier suppression technique. In our case, such a system is dedicated to the optical distribution of high spectral purity microwave signals in future satellite payloads. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1634–1637, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22544