Ilgin Seker

Tracking F-region plasma depletion bands using GPS-TEC, incoherent scatter radar, and all-sky imaging at Arecibo

F-region plasma dynamics has been one of the main foci of the ionospheric research community for decades. The mid-latitude F-region has been considered to be relatively calm; however recent observations using highly sensitive CCD imaging systems and Global Positioning System (GPS) receivers have revealed that mid-latitude F-region mesoscale electrodynamics are more complex and this region is more active than usually assumed. Here we report combined incoherent scatter radar (ISR), imager, and GPS observations of F-region Medium-Scale Traveling Ionospheric Disturbance (MSTID) structures over the Arecibo Observatory in Puerto Rico. In particular, the plasma structures seen in the narrow-beam ISR cannot be understood fully without the all-sky images, which provide the context for the radar results—specifically, the spatial and temporal properties of the mesoscale structure. The GPS-derived total electron content (TEC) data provide additional information on the intensity of the MSTIDs. Here we present analysis of two specific plasma depletion events, which we prefer to call “MSTID bands”. Important results on the 3D geometry of these structures were found using a newly developed observation technique. For the first time, it is shown that the southern part of MSTID bands reaches higher altitudes than the northern part (vertically tilted by 12° towards magnetic south). These results give a much broader perspective on nighttime, mid-latitude F-region structure and point to new ways of interpreting these structures and how they appear in ISR results.

UWB 3D near-field imaging with a sparse MIMO antenna array for concealed weapon detection

An ultra-wide-band (UWB) multiple-input multiple-output (MIMO) radar with a sparse array is designed and manufactured for three-dimensional near-field imaging applications such as concealed weapon detection. Contrary to existing mmW imaging radars, UWB components working in the lower microwave frequencies are more cost effective and yield images with resolutions satisfactory for contraband detection while not raising concerns related to personal privacy. A UWB sparse array provides resolution values equivalent to a fully populated array with a similar aperture size albeit with much fewer antenna elements, while yielding lower sidelobe levels compared to a narrowband sparse array. Performance of the proposed system is studied using a full-wave electromagnetic simulation environment which is capable of modelling the antenna array, the environment and the target in 3D while allowing modifications in mechanical and electrical properties of the materials. For image reconstruction, Kirchhoff-migration and back-projection algorithms are used and performances of these algorithms are compared. The effects of the spatial and temporal frequency response of the antenna array as well as array calibration on the image quality are also studied. A prototype of UWB MIMO sparse antenna array in Archimedean spiral configuration with an RF switch matrix is manufactured. Measurements are performed using a stepped-frequency continuous waveform (SFCW) transceiver for various metallic and non-metallic targets. It is observed that these targets are identifiable in the images formed based on measurement data. Consequently, promising concealed weapon detection performance is demonstrated with full-wave electromagnetic simulation and experimental results.

Erratum to: Dependence of mesospheric Na and Fe distributions on electron density at Arecibo

Author details Space and Atmospheric Sciences, Arecibo Observatory, SRI International, Arecibo, PR, USA. Electrical and Computer Engineering Department, Miami University, Oxford, OH, USA. Department of Physics, Indian Institute of Technology Roorkee, Roorkee 247667, Uttarakhand, India. Radar Space Sciences Laboratory, The Pennsylvania State University, 323 Electrical Engineering East, University Park, PA, USA. Radar Systems Engineering Department Radar, Intelligence ASELSAN Inc, Ankara, Turkey.

A new 3D display format relating azimuth-scanning radar data and all-sky images

We combine all-sky images of 630 nm airglow with the 3D structure of electron densities in the F-region above Arecibo. The line-of-sight electron densities obtained from the two azimuth-scanning beams of Arecibo incoherent scatter radar (ISR) are plotted in cone-shaped 3D visualizations along with horizontal projections of 630 nm airglow images. Displays of data in this new format from a night with ionospheric plasma irregularities demonstrate the improved perspective of the new format in revealing the 3D structure and evolution of the ionospheric plasma features over that provided by separate 2D plots in latitude and longitude for the all-sky airglow images and in height and time for the ISR electron densities.

Multi-instrument observations of an MSTID over Arecibo Observatory

The Penn State All-Sky Imager (PSASI) at Arecibo Observatory provides planar horizontal context to the vertical ionospheric profiles obtained by the Incoherent Scatter Radar (ISR). Electric field measurements from the Communication/Navigation Outage Forecast System (C/NOFS) satellite are mapped down geomagnetic field lines to the height of the airglow layer, allowing multi-instrument studies of field-aligned irregularities with radar, imager, and satellite. A Medium-Scale Traveling Ionospheric Disturbance (MSTID) was observed during such a conjunction near the December solstice of 2009.