DARWIN Digitale Dissertationen German Version Strich

FU Berlin
Digitale Dissertation

Stefan Heise :
Reconstruction of 3 dimensional electron density distributions based on GPS measurements from CHAMP
Rekonstruktion dreidimensionaler Elektronendichteverteilungen basierend auf CHAMP-GPS-Messungen

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Abstract

The Ionosphere denotes that part of the upper atmosphere which affects significantly radio wave propagation due to its ionization. This property causes as well the scientific interest in the ionosphere. Radio waves used for signal transmission by numerous technical systems are affected by the ionosphere. Above altitudes of about 1000 km the ionosphere fades to the so called plasmasphere. For the correction and simulation of ionospheric/plasmaspheric impacts on radio wave propagation, models of the ionosphere and plasmasphere are needed. A basic requirement for the understanding and modeling of the ionosphere/plasmasphere system are observation data. Due to the difficult observation conditions, the exploration of the upper ionosphere and especially of the plasmasphere is indeed sparse up to now. Existing models are based on comparatively small data sets and are therefore still deficient in some cases. In front of this background, the collection of new ionospheric/plasmaspheric observation data is worthwhile and necessary. The global navigation satellite system GPS uses two different L-band carrier frequencies for signal transmission. The ionosphere represents a dispersive propagation medium for this frequency range. Therefore, simultaneous reception of both GPS signals enables remote sensing of the ionosphere, assuming identical ray paths. Ground based GPS measurements are used successfully since several years to monitor the vertical Total Electron Content (TEC) in an operational manner. The installation of GPS receivers on board of LEO (Low Earth Orbiting) satellites such as CHAMP offers new opportunities of ionospheric/plasmaspheric remote sensing. For precise orbit determination the German small satellite CHAMP performs permanently dual frequency measurements of up to 8 GPS satellites with a sampling rate of 0.1 Hz, using a dedicated zenith looking antenna. These navigation measurements provide for the first time the opportunity of a GPS based monitoring of the upper ionosphere and plasmasphere on global scale. This PhD thesis describes the reconstruction of global three dimensional electron density distributions of the upper ionosphere and plasmasphere based on GPS measurements from CHAMP. The methods and algorithms that have been developed in this frame are pointed out in detail. After preprocessing and calibration, link related TEC measurements are derived from the GPS navigation observations on board CHAMP. The three dimensional electron density distribution is reconstructed by assimilating the integrated TEC measurements of a full CHAMP revolution into the ionospheric/plasmaspheric model PIM. For this purpose the discretization of PIM on a global voxel structure is necessary. The assimilation method which has been developed is based on an iterative algorithm. During this procedure the initial model assumption is modified in an multiplicative manner. Finally, the resulting electron density distribution represents the TEC measurements, which had been to assimilate. The reconstruction results are presented for selected assimilation examples by means of two dimensional slices along the respective CHAMP orbit plane. First validation results using electron density measurements from the Langmuir Probe on board CHAMP, from incoherent scatter radars and from ionosondes are promising and show the fundamental suitability of the presented technique for the reconstruction of adequate electron density information from integrated TEC measurements. Considering especially the reconstruction opportunities using GPS measurements of planned LEO missions in the future, such assimilation results may provide a considerable data base for ionospheric/plasmaspheric modeling and research.

Table of Contents

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TITELBLATT UND INHALT
1. EINFÜHRUNG UND ZIELSTELLUNG 3
2. DIE IONOSPHÄRE UND PLASMASPHÄRE DER ERDE 6
2.1. Einordnung innerhalb der Erdatmosphäre 6
2.2. Der Aufbau der Ionosphäre 9
2.3. Räumliche und zeitliche Variabilität der Ionosphäre 11
2.4. Atmosphärische Beeinflussung elektromagnetischer Wellen 13
2.5. Bedeutung der Ionosphäre 17
2.6. Die Plasmasphäre 19
2.7. Beobachtung der Ionosphäre und Plasmasphäre 21
2.8. Tomographie der Ionosphäre 26
2.9. Modelle der Ionosphäre 31
3. DIE CHAMP-MISSION 35
3.1. Wissenschaftliche Ziele 35
3.2. Satellit und wissenschaftliche Instrumente 35
3.3. Mission und Orbit 37
4. FERNERKUNDUNG DER IONOSPHÄRE MIT GPS 38
4.1. Das Global Positioning System 38
4.2. GPS-Messgrößen und die Beobachtungsgleichung 43
4.3. Bestimmung des TEC aus den GPS-Beobachtungen 45
5. PROZESSIERUNG DER CHAMP-GPS-DATEN ZUR ABLEITUNG VON TEC-INFORMATIONEN 47
5.1. Verwendete Daten 47
5.2. ProzessierungsÜbersicht und automatische Prozessierung 50
5.3. Sicherung der GPS-Datenqualität 54
5.4. Kalibrierung der relativen TEC-Messungen 59
6. ABLEITUNG LOKALER ELEKTRONENDICHTEN AUS DEN INTEGRALEN TEC-INFORMATIONEN 68
6.1. Die Voxel-Struktur 68
6.2. Assimilation der TEC-Daten 73
7. ERGEBNISSE UND DISKUSSION 85
7.1. Ergebnisse der Datenassimilation 85
7.2. Validierung rekonstruierter Elektronendichteverteilungen mit unabhÄngigen ionosphärischen Daten 89
8. ZUSAMMENFASSUNG UND AUSBLICK 101
9. LITERATUR 104

More Information:

Online available: http://www.diss.fu-berlin.de/2002/273/indexe.html
Language of PhDThesis: german
Keywords: ionosphere, plasmasphere, GPS, CHAMP, electron density
DNB-Sachgruppe: 31 Geowissenschaften
Date of disputation: 03-Dec-2002
PhDThesis from: Fachbereich Geowissenschaften, Freie Universität Berlin
First Referee: Prof. Dr. Horst Malberg
Second Referee: Prof. Dr. Justus Notholt
Contact (Author): stefan.heise@dlr.de
Date created:05-Dec-2002
Date available:17-Dec-2002

 

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