Studies of Electrostatic Waves, VLF-wave Particle Interactions, and Propagations in the Ionosphere
Abstract : The long-term goal of this project is to study waves, irregularities, and propagation in the earth s ionosphere, particularly with respect to GPS. The project has two foci: first, to understand how the ionosphere affects GPS signals and second, how GPS can be used for remote sensing of the ionosphere. In association with these goals, we additionally conduct in situ experiments on satellites and sounding rockets to directly measure ionospheric waves and irregularities that affect signal propagation.
Medical ultrasound imaging is a non-invasive technique for clinical diagnosis, but its applications are limited by the low image quality. In this paper, the problem of ultrasound imaging is dealt with by a novel deconvolution method which utilizes the envelope of the point spread function (EPSF) instead of the commonly used point spread function (PSF). The EPSF is estimated based on minimum phase assumption without considering phase unwrapping and linear phase elimination, thus it is much efficient and reliable. After obtaining the EPSF, an l 1 -norm regularized optimization model is derived and efficiently solved by an augmented Lagrangian method (ALM). Experiments are conducted on both simulated and in vivo data. The results show that the proposed deconvolution method can provide significantly improved ultrasound images in terms of resolution gain and signal to noise ratio.