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Detection and localization of F-layer ionospheric irregularities with the back-propagation method along the radio occultation ray path
Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.ORCID iD: 0000-0002-7769-8641
Beyond Gravity Sweden Ab.
Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.ORCID iD: 0000-0002-2856-6140
Beyond Gravity Sweden Ab.ORCID iD: 0000-0002-0620-7825
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2023 (English)In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 16, no 7, p. 1849-1864Article in journal (Refereed) Published
Abstract [en]

The back propagation (BP) method consists of diffractive integrals computed over a trajectory path, projecting a signal to different planes. It unwinds the diffraction and multipath, resulting in minimum disturbance on the BP amplitude when the auxiliary plane coincides with the region causing the diffraction. The method has been previously applied in GNSS Radio Occultation (RO) measurements showing promising results in the location estimate of ionospheric irregularities but without complementary data to validate the estimation. In this study, we investigate with wave optics propagator (WOP) simulations of an equatorial C/NOFS occultation with scintillation signatures caused by an equatorial plasma bubble (EPB), which was parametrized with aid of collocated data. In addition, a few more test cases were designed to assess the BP method regarding size, intensity and placement of single and multiple irregularity regions. The results show a location estimate accuracy of 10 km (single bubble, reference case), where in multiple bubble scenarios only the strongest disturbance would be resolved properly. The minimum detectable disturbance level and the estimation accuracy depend on the receiver noise level, and in the case of several bubbles on the distance between them. The remarks of the evaluation supported the interpretation of results for two COSMIC occultations.

Place, publisher, year, edition, pages
Copernicus Publications , 2023. Vol. 16, no 7, p. 1849-1864
National Category
Meteorology and Atmospheric Sciences
Research subject
Systems Engineering
Identifiers
URN: urn:nbn:se:bth-22798DOI: 10.5194/amt-2022-57ISI: 000962705900001Scopus ID: 2-s2.0-85152796342OAI: oai:DiVA.org:bth-22798DiVA, id: diva2:1647594
Projects
Swedish National Space Board, NRFP-4
Funder
Swedish National Space BoardAvailable from: 2022-03-28 Created: 2022-03-28 Last updated: 2023-05-01Bibliographically approved
In thesis
1. On the Ionospheric Influence on GNSS Radio Occultation Signals: Modelling and Assessment
Open this publication in new window or tab >>On the Ionospheric Influence on GNSS Radio Occultation Signals: Modelling and Assessment
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Radio Occultation (RO) is a well-established remote sensing technique that uses Global Navigation Satellite System (GNSS) signals to sound the Earth’s atmosphere. GNSS-RO measurements provide high-resolution, vertical profiles of physical parameters from the lower atmosphere (troposphere and stratosphere), e.g., refractivity, dry temperature, pressure, and water vapour, with primary application in weather forecasting and climatology models. The upper atmosphere (ionosphere) is also sounded during measurements, in which information about total electron content, electron density profiles, and scintillation indices compose the RO ionospheric data product.

The ionosphere is a dispersive medium composed of ionized particles. It is extensively conditioned by Solar activity and shows seasonal, geographical, and day- and night-time variation. Despite the benefit of the upper atmospheric data, the ionosphere influences the retrievals in the lower atmosphere by (i) adding an inherent systematic bias in bending angles, i.e., residual ionospheric error (RIE), and (ii) disturbing the signal amplitude and phase, i.e., scintillation, in the presence of irregularities regions on the electron density along the ray path, e.g., equatorial plasma bubbles. In this dissertation, both aspects are investigated by modelling the equatorial ionosphere, and its small-scale irregularities in simulations of occultation events to (i) reproduce the effects observed in measurements and (ii) assess methods that can extract information about the ionosphere and support its monitoring and modelling.

The multiple phase screen method was applied to model the GNSS signal propagation through quiet and disturbed ionospheric conditions. The small-scale irregularities in the F-region were modelled by a single slope power law to yield moderate to strong scintillation in the signals. Results were assessed according to the amplitude and phase scintillation indices, RIE, the standard deviation of the retrieved bending angles, and power spectral density (PSD). A subset of these parameters was taken as features to train a classifier based on the support vector machine algorithm. The purpose of this model was to detect RO measurements affected by ionospheric scintillation. Specifically, those in which PSD could provide further information about the irregularities according to the scintillation theory. Additionally, the back propagation (BP) method and its capability to estimate the mean distance between the receiver and irregularities were evaluated.

Applying spectral analysis techniques to RO measurements may contribute to the characterization of small-scale irregularities in equatorial plasma bubbles. The results from simulations applying the single-slope power law to model the irregularities showed a good agreement with the selected cases. The automatic detection of occultations affected by ionospheric irregularities has achieved similar performance to models trained with ground-based measurements. Furthermore, the BP method can add the estimation of the mean location to the spectral analysis information. Such tools can enlarge the amount of ionospheric data retrieved -- especially for occultations with extended vertical range and when combined with other sounding techniques.

Place, publisher, year, edition, pages
Karlskrona: Blekinge Tekniska Högskola, 2022
Series
Blekinge Institute of Technology Doctoral Dissertation Series, ISSN 1653-2090 ; 2022:03
Keywords
Remote Sensing, Radio Occultation, Ionosphere, Scintillation, Wave Optics Propagator, Spectral Analysis, Plasma Bubble
National Category
Remote Sensing
Research subject
Systems Engineering
Identifiers
urn:nbn:se:bth-22836 (URN)978-91-7295-439-7 (ISBN)
Public defence
2022-05-25, 413A + Zoom, Campus Gräsvik, Karlskrona, 08:15 (English)
Opponent
Supervisors
Projects
NRFP
Funder
Swedish National Space Board
Available from: 2022-04-13 Created: 2022-04-13 Last updated: 2022-05-02Bibliographically approved

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Ludwig Barbosa, ViníciusSievert, ThomasPettersson, MatsVu, Viet Thuy

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