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Sievert, T., Rasch, J., Carlström, A. & Pettersson, M. (2018). Analysis of reflections in GNSS radio occultation measurements using the phase matching amplitude. Atmospheric Measurement Techniques, 11(1), 569-580
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
Sievert, T., Rasch, J., Carlström, A., Pettersson, M. & Vu, V. T. (2018). Comparing reflection signatures in radio occultation measurements using the full spectrum inversion and phase matching methods. In: Comeron A.,Kassianov E.,Picard R.H.,Schafer K.,Weber K. (Ed.), PROCEEDINGS VOLUME 10786; Remote Sensing of Clouds and the Atmosphere XXIII: . Paper presented at Remote Sensing of Clouds and the Atmosphere XXIII 2018; Berlin; Germany; 12 September 2018 through 13 September 2018. SPIE - International Society for Optical Engineering, Article ID 107860A.
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
Sievert, T., Rasch, J., Anders, C., Pettersson, M. & Vu, V. T. (2017). Determining the refractivity at the bottom of the atmosphere using radio occultation. In: 2017 IEEE International Geoscience and Remote Sensing Symposium (IGARSS): . Paper presented at 2017 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), Fort Worth (pp. 4433-4436). IEEE
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
Danielsson, M., Sievert, T., Grahn, H. & Rasmusson, J. (2016). Feature Detection and Description using a Harris-Hessian/FREAK Combination on an Embedded GPU. In: : . Paper presented at 5th Int’l Conf. on Pattern Recognition Applications and Methods (ICPRAM), Rome. Springer
Open this publication in new window or tab >>Feature Detection and Description using a Harris-Hessian/FREAK Combination on an Embedded GPU
2016 (English)Conference paper, Published paper (Refereed)
Abstract [en]

GPUs in embedded platforms are reaching performance levels comparable to desktop hardware, thus it becomes interesting to apply Computer Vision techniques. We propose, implement, and evaluate a novel feature detector and descriptor combination, i.e., we combine the Harris-Hessian detector with the FREAK binary descriptor. The implementation is done in OpenCL, and we evaluate the execution time and classification performance. We compare our approach with two other methods, FAST/BRISK and ORB. Performance data is presented for the mobile device Xperia Z3 and the desktop Nvidia GTX 660. Our results indicate that the execution times on the Xperia Z3 are insufficient for real-time applications while desktop execution shows future potential. Classification performance of Harris-Hessian/FREAK indicates that the solution is sensitive to rotation, but superior in scale variant images.

Place, publisher, year, edition, pages
Springer, 2016
Keywords
GPU, Feature Detection, Feature Description, Mobile devices
National Category
Computer Sciences Computer Vision and Robotics (Autonomous Systems)
Identifiers
urn:nbn:se:bth-11444 (URN)
Conference
5th Int’l Conf. on Pattern Recognition Applications and Methods (ICPRAM), Rome
Projects
BigData@BTH - Scalable resource-efficient systems for big data analyticsIndustrial Excellence Center EASE - Embedded Applications Software Engineering
Funder
Knowledge Foundation, 20140032VINNOVA
Available from: 2016-01-19 Created: 2016-01-19 Last updated: 2018-02-02Bibliographically approved
Danielsson, M., Grahn, H., Sievert, T. & Rasmusson, J. Comparing Two Generations of Embedded GPUs Running a Feature Detection Algorithm.
Open this publication in new window or tab >>Comparing Two Generations of Embedded GPUs Running a Feature Detection Algorithm
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Graphics processing units (GPUs) in embedded mobile platforms are reaching performance levels where they may be useful for computer vision applications. We compare two generations of embedded GPUs for mobile devices when run- ning a state-of-the-art feature detection algorithm, i.e., Harris- Hessian/FREAK. We compare architectural differences, execu- tion time, temperature, and frequency on Sony Xperia Z3 and Sony Xperia XZ mobile devices. Our results indicate that the performance soon is sufficient for real-time feature detection, the GPUs have no temperature problems, and support for large work-groups is important.

National Category
Computer Systems
Identifiers
urn:nbn:se:bth-16554 (URN)
Projects
BigData@BTH - Scalable resource-efficient systems for big data analyticsEASE - Embedded Applications Software Engineering
Funder
Knowledge Foundation, 20140032VINNOVA
Available from: 2018-06-19 Created: 2018-06-19 Last updated: 2018-06-27Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-2856-6140

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