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GNSS Radio Occultation Inversion Methods and Reflection Observations in the Lower Troposphere
Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.ORCID iD: 0000-0002-2856-6140
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

GNSS Radio Occultation (GNSS-RO) is an opportunistic Earth sensing technique where GNSS signals passing through the atmosphere are received in low Earth orbit and processed to extract meteorological parameters. As signals are received along an orbit, the measured Doppler shift is transformed to a bending angle profile (commonly referred to as bending angle retrieval), which, in turn, is inverted to a refractivity profile. Thanks to its high vertical resolution and SI traceability, GNSS-RO is an important complement to other Earth sensing endeavors. In the lower troposphere, GNSS-RO measurements often get degraded and biased due to sharp refractive gradients and other complex structures. The main objective of this thesis is to explore contemporary retrieval methods such as phase matching and full spectrum inversion to improve their performance in these conditions. To avoid the bias caused by the standard inversion, we attempt to derive additional information from the amplitude output of the examined retrieval operators. While simulations indicate that such information could be found, it is not immediately straightforward how to achieve this with real measurements. The approach chosen is to examine reflected signal components and their effect on the amplitude output.

Place, publisher, year, edition, pages
Karlskrona: Blekinge Tekniska Högskola, 2019. , p. 77
Series
Blekinge Institute of Technology Licentiate Dissertation Series, ISSN 1650-2140 ; 4
Keywords [en]
GNSS Radio Occultation (GNSS-RO)
National Category
Remote Sensing
Identifiers
URN: urn:nbn:se:bth-17484ISBN: 978-91-7295-368-0 (print)OAI: oai:DiVA.org:bth-17484DiVA, id: diva2:1277418
Presentation
2019-02-01, J1650, Blekinge Tekniska Högskola, Karlskrona, 09:00 (English)
Supervisors
Funder
Knowledge Foundation, 20140192Swedish National Space Board, 241/15Available from: 2019-01-11 Created: 2019-01-10 Last updated: 2019-03-05Bibliographically approved
List of papers
1. Determining the refractivity at the bottom of the atmosphere using radio occultation
Open this publication in new window or tab >>Determining the refractivity at the bottom of the atmosphere using radio occultation
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2017 (English)In: 2017 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), IEEE, 2017, p. 4433-4436Conference paper, Published paper (Refereed)
Abstract [en]

High accuracy of impact height is important to get reliableRadio Occultation (RO) measurements of the atmosphere refractivity.We have made an investigation on how accuratelywe can measure the impact height at ground level using waveoptics simulations, realistic refractivity profiles, a realisticsimulator for an advanced RO instrument including noise,and using phase matching for the inversion. The idea of theinvestigation is to increase the measurement accuracy of impactheight at low altitudes and to give reliable measurementseven in cases of super-refractive layers. We present statisticson the accuracy and precision of the determination of theimpact height at ground, as well as the resulting accuracy andprecision in the measured refractivity.

Place, publisher, year, edition, pages
IEEE, 2017
Series
IEEE International Symposium on Geoscience and Remote Sensing IGARSS, ISSN 2153-6996
Keywords
radio occultation, GPS, marine boundary layer
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:bth-15745 (URN)10.1109/IGARSS.2017.8127984 (DOI)000426954604121 ()978-1-5090-4951-6 (ISBN)
Conference
2017 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), Fort Worth
Available from: 2018-01-11 Created: 2018-01-11 Last updated: 2019-01-10Bibliographically approved
2. Analysis of reflections in GNSS radio occultation measurements using the phase matching amplitude
Open this publication in new window or tab >>Analysis of reflections in GNSS radio occultation measurements using the phase matching amplitude
2018 (English)In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 11, no 1, p. 569-580Article in journal (Refereed) Published
Abstract [en]

It is well-known that in the presence of super-refractive layers in the lower-tropospheric inversion of GNSSradio occultation (RO) measurements using the Abel trans-form yields biased refractivity profiles. As such it is problem-atic to reconstruct the true refractivity from the RO signal.Additional information about this lower region of the atmo-sphere might be embedded in reflected parts of the signal. Toretrieve the bending angle, the phase matching operator canbe used. This operator produces a complex function of theimpact parameter, and from its phase we can calculate thebending angle. Instead of looking at the phase, in this paperwe focus on the function’s amplitude. The results in this pa-per show that the signatures of surface reflections in GNSSRO measurements can be significantly enhanced when usingthe phase matching method by processing only an appropri-ately selected segment of the received signal. This signatureenhancement is demonstrated by simulations and confirmedwith 10 hand-picked MetOp-A occultations with reflectedcomponents. To validate that these events show signs of re-flections, radio holographic images are generated. Our resultssuggest that the phase matching amplitude carries informa-tion that can improve the interpretation of radio occultationmeasurements in the lower troposphere.

Place, publisher, year, edition, pages
Nicolaus Copernicus University Press, 2018
National Category
Remote Sensing Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:bth-15843 (URN)10.5194/amt-11-569-2018 (DOI)000449173700001 ()
Funder
Knowledge Foundation, 20140192Swedish National Space Board, 241/15
Note

open access

Available from: 2018-01-31 Created: 2018-01-31 Last updated: 2019-01-10Bibliographically approved
3. Comparing reflection signatures in radio occultation measurements using the full spectrum inversion and phase matching methods
Open this publication in new window or tab >>Comparing reflection signatures in radio occultation measurements using the full spectrum inversion and phase matching methods
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2018 (English)In: PROCEEDINGS VOLUME 10786; Remote Sensing of Clouds and the Atmosphere XXIII / [ed] Comeron A.,Kassianov E.,Picard R.H.,Schafer K.,Weber K., SPIE - International Society for Optical Engineering, 2018, article id 107860AConference paper, Published paper (Refereed)
Abstract [en]

Global Navigation Satellite System Radio Occultation (GNSS-RO) is an important technique used to sound the Earth's atmosphere and provide data products to numerical weather prediction (NWP) systems as well as toclimate research. It provides a high vertical resolution and SI-traceability that are both valuable complements toother Earth observation systems. In addition to direct components refracted in the atmosphere, many received RO signals contain reflected components thanks to the specular and relatively smooth characteristics of the ocean. These reflected components can interfere the retrieval of the direct part of the signal, and can also contain meteorological information of their own, e.g., information about the refractivity at the Earth's surface. While the conventional method to detect such reflections is by using radio-holographic methods, it has been shown that it is possible to see reflections using wave optics inversion, specically while inspecting the amplitude of the output of phase matching (PM). The primary objective of this paper is to analyze the appearance of these reflections in the amplitude output from another wave optics algorithm, namely the much faster full spectrum inversion (FSI). PM and FSI are closely related algorithms - they both use the method of stationary phase to derive the bending angle from a measured signal. We apply our own implementation of FSI to the same GNSS-RO measurements that PM was previously applied to and show that the amplitudes of the outputs again indicate reflection in the surface of the ocean. Our results show that the amplitudes output from the FSI and PM algorithms are practically identical and that the reflection signatures thus appear equally well.

Place, publisher, year, edition, pages
SPIE - International Society for Optical Engineering, 2018
Keywords
radio occultation, wave optics, re ections, full spectrum inversion
National Category
Meteorology and Atmospheric Sciences Signal Processing
Identifiers
urn:nbn:se:bth-17132 (URN)10.1117/12.2325386 (DOI)000453909700007 ()9781510621558 (ISBN)
Conference
Remote Sensing of Clouds and the Atmosphere XXIII 2018; Berlin; Germany; 12 September 2018 through 13 September 2018
Available from: 2018-10-16 Created: 2018-10-16 Last updated: 2019-01-10Bibliographically approved

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Citation style
  • apa
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Output format
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