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Enhanced Radar Backscatter from the Ionosphere
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.ORCID iD: 0000-0001-6802-1842
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. , p. xiii, 57
Series
Trita-EE, ISSN 1653-5146
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:kth:diva-116669ISBN: 978-91-7501-627-6 (print)OAI: oai:DiVA.org:kth-116669DiVA: diva2:600064
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
List of papers
1. Radar interferometer calibration of the EISCAT Svalbard Radar and a additional receiver station
Open this publication in new window or tab >>Radar interferometer calibration of the EISCAT Svalbard Radar and a additional receiver station
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2013 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 105-106, p. 287-292Article 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.

Keyword
Radio science (interferometry), Space plasma physics (instruments and techniques)
National Category
Natural Sciences Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-108331 (URN)10.1016/j.jastp.2012.11.017 (DOI)000328913100032 ()2-s2.0-84889594499 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20140122

Available from: 2012-12-20 Created: 2012-12-20 Last updated: 2017-12-06Bibliographically approved
2. Enhanced EISCAT UHF backscatter during high-energy auroral electron precipitation
Open this publication in new window or tab >>Enhanced EISCAT UHF backscatter during high-energy auroral electron precipitation
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2013 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 31, no 10, p. 1681-1687Article in journal (Refereed) Published
Abstract [en]

Natural enhancements in the backscattered power of incoherent scatter radars up to 5 orders of magnitudes above the thermal backscatter are sometimes observed at high latitudes. Recently observations of enhancements in the backscattered power including a feature at zero Doppler shift have been reported. These enhancements are limited in altitude to tens of kilometers. The zero Doppler shift feature has been interpreted as a signature of electron density cavitation. Enhanced plasma lines during these observations have also been reported. We report on the first EISCAT UHF observations of enhanced backscattered radar power including a zero Doppler shift feature. The enhancements originated from two distinct and intermittent layers at about 200 km altitude. The altitude extent of the enhancements, observed during auroral high-energy electron precipitation, was < 2 km.

Keyword
Ionosphere, Auroral ionosphere
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-116667 (URN)10.5194/angeo-31-1681-2013 (DOI)000326548600007 ()2-s2.0-84885789204 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20131129. Updated from manuscript to article in journal.

Available from: 2013-01-24 Created: 2013-01-22 Last updated: 2017-12-06Bibliographically approved
3. Observations of HF-induced instability in the auroral E region
Open this publication in new window or tab >>Observations of HF-induced instability in the auroral E region
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2013 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 31, no 6, p. 1103-1108Article in journal (Refereed) Published
Abstract [en]

Enhancements were observed in backscattered radar power during an ionospheric heating experiment from two distinct altitude regions in the auroral E region above Tromso. For the experiment the EISCAT Tromso heater was operated with O mode and X mode alternated at 4.04 MHz, close to the 3rd electron gyroharmonic. Ion-line data recorded with the EISCAT UHF radar reveal different temporal evolutions as well as different ion-line characteristics for the enhancements from the two altitude regions. The upper layer is dominated by a strong central feature, whereas the lower layer has three peaks corresponding to the central feature and the two ion lines. The altitude region of the two closely spaced (altitude separation similar to 5 km) but distinct enhancements is close to the critical altitude for the heater wave.

Keyword
Ionosphere, active experiments
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-116668 (URN)10.5194/angeo-31-1103-2013 (DOI)000322290400009 ()2-s2.0-84895810969 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20130830. Updated from manuscript to article in journal.

Previous title: Studies of HF induced instabilities in the auroral E-region

Available from: 2013-01-24 Created: 2013-01-22 Last updated: 2017-12-06Bibliographically approved

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