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Radar interferometer calibration of the EISCAT Svalbard Radar and a additional receiver station
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.ORCID iD: 0000-0001-6802-1842
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.ORCID iD: 0000-0003-2422-5426
Department of Physics, University in Tromsø.
Show others and affiliations
2013 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 105-106, 287-292 p.Article in journal (Refereed) Published
Abstract [en]

The EISCAT Svalbard Radar has two parabolic dishes. In order to attempt to implement radar aperture synthesis imaging methods three smaller, passive receive array antennas were built. Several science goals for this new receiver system exist, the primary of which is to study so called naturally enhanced ion acoustic lines. In order to compare radar aperture synthesis imaging results with measurements from optical imagers, calibration of the radar interferometer system is necessary. In this work we present the phase calibration of the EISCAT Svalbard interferometer including one array antenna. The calibration was done using the coherent scatter from satellites passing through the radar beam. Optical signatures of the satellite transits provide accurate position for the satellites. By using transits of a number of satellites sufficient for mapping the radar beam, the interferometric cross-phase was fitted within the radar beam. The calibration technique presented in this work will be applied to all antenna pairs of the antenna configuration for future interferometry studies.

Place, publisher, year, edition, pages
2013. Vol. 105-106, 287-292 p.
Keyword [en]
Radio science (interferometry), Space plasma physics (instruments and techniques)
National Category
Natural Sciences Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-108331DOI: 10.1016/j.jastp.2012.11.017ISI: 000328913100032Scopus ID: 2-s2.0-84889594499OAI: oai:DiVA.org:kth-108331DiVA: diva2:580047
Funder
Swedish Research Council
Note

QC 20140122

Available from: 2012-12-20 Created: 2012-12-20 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Enhanced Radar Backscatter from the Ionosphere
Open this publication in new window or tab >>Enhanced Radar Backscatter from the Ionosphere
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Incoherent scatter radars are powerful ground based instruments for ionospheric measurements. By analysis of the Doppler shifted backscatter spectrum, containing the signature of electrostatic plasma waves, plasma bulk properties are estimated. Occasionally, the backscattered radar power is enhanced several orders of magnitude above the thermal backscatter level. These enhancements occur during naturally disturbed ionospheric conditions and in ionospheric modi_cation experiments, where a powerful radio wave is incident on the ionospheric plasma. In both of the cases the non-linearity is thought to be turbulence of electrostatic Langmuir waves. The Langmuir turbulence theory and models account for many features of enhanced ionospheric radar backscatter reported on in the literature. During disturbed conditions, with precipitation of auroral electrons, Langmuir turbulence is thought to be driven by a low energy electron beam. Optical and radar observations of naturally enhanced radar backscatter indicate Alfvénic type of aurora during events reported on in the literature. However, contrasting conclusions have been drawn from optical observations. While some reports suggest that enhanced radar backscatter is observed at the edge of auroral structures others suggest that the enhanced backscatter region and auroral precipitation are co-located. Optical imagers with a narrow field of view resolve auroral structures with tens of meters scale size. The cross beam resolution of radars, however, is limited by the width of the radar beam, typically several kilometers wide at auroral altitudes. By using several radar receivers for observations - radar interferometry - the cross beam resolution is increased. Simultaneous observations of enhanced radar backscatter with radar interferometry and narrow field of view optical observations will increase the understanding of the physical processes involved and will make it possible to associate auroral structures with the enhanced radar backscatter. An interferometric radar receiver system has been built and a calibration technique for the system developed. In ionospheric modification experiments, the Langmuir turbulence is driven by a powerful electromagnetic wave incident on the ionosphere and electrons are significantly accelerated. The acceleration of electrons is not yet fully understood. Ionospheric modification experiments and ground based measurements, as reported on herein, contribute to the understa

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. xiii, 57 p.
Series
Trita-EE, ISSN 1653-5146
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-116669 (URN)978-91-7501-627-6 (ISBN)
Presentation
2013-02-22, Seminarierummet, Teknikringen 31, KTH, Stockholm, 13:15 (English)
Opponent
Supervisors
Note

QC 20130131

Available from: 2013-01-31 Created: 2013-01-22 Last updated: 2013-08-30Bibliographically approved
2. Radar Signatures of Auroral Plasma Instability
Open this publication in new window or tab >>Radar Signatures of Auroral Plasma Instability
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Incoherent scatter radars are powerful ground based instruments for ionospheric measurements. By analysis of the Doppler shifted backscatter spectrum, containing the signature of electrostatic plasma waves, plasma bulk properties are estimated. At high latitudes the backscattered radar power is occasionally enhanced several orders of magnitude above the thermal backscatter level. These enhancements occur during geomagnetic disturbed conditions and are referred to as naturally enhanced ion acoustic echoes (NEIALs). NEIALs are linked to auroral activity with optical auroral emission observed in the vicinity of the radar measurement volume simultaneously to NEIALs. The backscatter enhancements are thought to be caused by wave activity above thermal level due to instability. A number of theories have been put forward including streaming instabilities and Langmuir turbulence to explain NEIAL observations. NEIALs occur in two classes distinct by their Doppler features. Observations of the first type, which has been studied more extensively, are generally modelled well by the Langmuir turbulence model. The difficulty in trying to understand the driving mechanism of the instability is the limited spatial resolution of the radar measurements. Observations of the second type, reported on more recently, have been interpreted as evidence for naturally occurring strong Langmuir turbulence by means of their Doppler features.

Aperture synthesis is a technique to increase the spatial resolution of the radar measurements to below beam width of the single receiver antennas. The technique is employed to investigate the structure of NEIALs in the plane perpendicular to the magnetic field at sub-degree scale corresponding to hundreds of meters to a few kilometres at ionospheric altitudes. Calibration of the radar interferometer is necessary and a calibration technique is presented in paper I. Interferometry observations of a NEIAL event with receivers deployed at the EISCAT incoherent scatter radar on Svalbard are presented in paper II. The size of the enhanced backscatter region is found to be limited to 900 x 500m in the plane perpendicular to the geomagnetic field. These observations constitute the first unambiguous measurements giving evidence for the limited size of the enhanced backscatter region.

In paper III observations of strong Langmuir turbulence signatures are presented. The apparent turbulent region in these observations is limited to two narrow altitude regions, 2km extent, and electron density irregularities caused by the turbulence are thought to reach down to decimeter scale length. The turbulence observations were obtained during energetic electron precipitation thereby differing from other observations during which a low energy component in the electron precipitation is reported. In paper IV a statistical study of strong Langmuir turbulence radar signatures is presented. The study reveals differing local time distributions for these signatures from type I NEIALs indicating di_ering driving conditions for the two types of NEIALs. It is found that strong Langmuir turbulence signatures are predominantly observed in the pre-midnight sector where auroral break-up aurora prevails.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xv, 65 p.
Series
TRITA-EE, ISSN 1653-5146 ; 2015:007
Keyword
Ionosphere, Particle Precipitation, Instability, Plasma Turbulence
National Category
Fusion, Plasma and Space Physics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-160894 (URN)978-91-7595-442-4 (ISBN)
Public defence
2015-03-27, F3, Lindstedtsvägen 26, KTH, Stockholm, 09:56 (English)
Opponent
Supervisors
Note

QC 20150303

Available from: 2015-03-03 Created: 2015-03-03 Last updated: 2015-03-03Bibliographically approved

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