Browsing by Author "Close, Sigrid"
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Item Restricted Inverse filtering of radar signals using compressed sensing with application to meteors(American Geophysical Union, 2012-09-12) Volz, Ryan; Close, SigridCompressed sensing, a method which relies on sparsity to reconstruct signals with relatively few measurements, provides a new approach to processing radar signals that is ideally suited to detailed imaging and identification of multiple targets. In this paper, we extend previously published theoretical work by investigating the practical problems associated with this approach. In deriving a discrete linear radar model that is suitable for compressed sensing, we discuss what the discrete model can tell us about continuously defined targets and show how sparsity in the latter translates to sparsity in the former. We provide details about how this problem can be solved when using large data sets. Through comparisons with matched filter processing, we validate our compressed sensing technique and demonstrate its application to meteors, where it has the potential to answer open questions about processes like fragmentation and flares. At the cost of computational complexity and an assumption of target sparsity, the benefits over pulse compression using a matched filter include no filtering sidelobes, noise removal, and higher possible range and Doppler frequency resolution.Item Open Access Measuring MLT winds by tracking meteor trails with incoherent scatter radar: a new method observes rapidly changing winds exceeding 500km/Hr(Instituto Geofísico del Perú, 2009) Oppenheim, Meers; Sugar, Glenn; Slowey, Nick; Bass, Elizabeth; Chau Chong Shing, Jorge Luis; Close, SigridDiapositivas presentadas en: CEDAR Workshop 2009 del 28 de junio al 2 de julio de 2009 en Santa Fe, Nuevo México, USA.Item Open Access Remote sensing lower thermosphere wind profiles using non-specular meteor echoes(American Geophysical Union, 2009-05-12) Oppenheim, Meers M.; Sugar, Glenn; Slowey, Nicholas O.; Bass, Elizabeth; Chau Chong Shing, Jorge Luis; Close, SigridThis article describes a new method of measuring wind velocity profiles between 93 km and 110 km altitude by tracking non‐specular meteor echoes as neutral winds transport the plasma trails. This requires a large VHF radar with interferometric capability able to point nearly perpendicular to the geomagnetic field. A small data sample from the Jicamarca Radio Observatory allows the measurement of horizontal wind speeds and directions with a range resolution of a few hundred meters. These observations show speeds reaching 150 m/s and sometimes changing by as much as 100 m/s over a 6 km altitude range. At the best times, these measurements can be made with only a few minutes of data. With some refinement of the data collection and analysis techniques, this technique should produce high resolution images of lower thermospheric winds as they change in both altitude and time.Item Open Access Using non-spectacular radar meteor echoes to monitor lower thermosphere wind profiles(Instituto Geofísico del Perú, 2009) Oppenheim, Meers; Sugar, Glenn; Bass, Elizabeth; Slowey, Nick; Chau Chong Shing, Jorge Luis; Close, SigridWe present a new method of measuring lower thermospheric wind velocity profiles by tracking non‐specular meteor echoes in time. This approach relies on having a radar following plasma irregularities as they are dragged by the neutral wind. This requires a VHF radar with interferometric capability able to point close to perpendicular to the geomagnetic field. Using a small sample of data from the Jicamarca Radio Observatory, we calculated wind speeds and directions between 90 and 110\ km with a range resolution of a few hundred meters. The measurements taken show speeds reaching 150m/s and someAmes changing by as much as 100m/s over a 6km altitude range. With some refinement of the data collection and analysis techniques, we expect that one could obtain high resolution images of lower thermospheric winds as they change in both altitude and time. We will discuss these results, the physics underlying these measurements, and the limitations.