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Auteur K. Larson |
Documents disponibles écrits par cet auteur (6)
Ajouter le résultat dans votre panier Affiner la recherche Interroger des sources externesVegetation sensing using GPS-interferometric reflectometry: theoretical effects of canopy parameters on signal-to-noise ratio data / C.C. Chew in IEEE Transactions on geoscience and remote sensing, vol 53 n° 5 (mai 2015)
Titre : Vegetation sensing using GPS-interferometric reflectometry: theoretical effects of canopy parameters on signal-to-noise ratio data Type de document : Article/Communication Auteurs : C.C. Chew, Auteur ; E.E. Small, Auteur ; K. Larson, Auteur ; V. Zavorotny, Auteur Année de publication : 2015 Article en page(s) : pp 2755 - 2764 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] couvert végétal
[Termes IGN] humidité du sol
[Termes IGN] rapport signal sur bruit
[Termes IGN] réflectométrie par GNSS
[Termes IGN] signal GPS
[Termes IGN] végétationRésumé : (Auteur) The potential to use GPS signal-to-noise ratio (SNR) data to estimate changes in vegetation surrounding a ground-based antenna is evaluated. A 1-D plane-stratified model that simulates the response of GPS SNR data to changes in both soil moisture and vegetation is presented. The model is validated against observations of SNR data from four field sites with varying vegetation cover. Validation shows that the average correlation between modeled and observed SNR data is higher than the average correlation between concurrent SNR observations from different satellite tracks at a site. The model also reproduces variations in the SNR metrics amplitude, phase, and effective reflector height over a range of vegetation wet weights from 0 to 4 kg · m-2, with r2 values of 0.79, 0.84, and 0.62, respectively. Model simulations indicate that the amplitude of SNR oscillations may be used to estimate vegetation amount when vegetation wet weight is below 1.5 kg · m-2. When vegetation wet weight exceeds 1.5 kg · m-2, the sensitivity of amplitude to changes in vegetation amount decreases. Phase of SNR oscillations also varies consistently with vegetation up to 1.5 kg · m-2. However, phase is also very sensitive to soil moisture variations, thus limiting its utility for estimating vegetation. Effective reflector height is not a consistent indicator of vegetation change. Beyond 1.5 kg · m-2, the constant frequency assumption used to characterize SNR fluctuations does not adequately describe observed data. A more complex approach than the standard SNR metrics used here is required to extend GPS-Interferometric Reflectometry sensing to thicker canopies. Numéro de notice : A2015-517 Affiliation des auteurs : non IGN Thématique : FORET/POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1109/TGRS.2014.2364513 En ligne : https://doi.org/10.1109/TGRS.2014.2364513 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=77523
in IEEE Transactions on geoscience and remote sensing > vol 53 n° 5 (mai 2015) . - pp 2755 - 2764[article]Exemplaires(1)
Code-barres Cote Support Localisation Section Disponibilité 065-2015051 RAB Revue Centre de documentation En réserve L003 Disponible
Titre : It's not all bad, understanding and using GNSS multipath Type de document : Article/Communication Auteurs : A. Bilich, Auteur ; K. Larson, Auteur Année de publication : 2009 Article en page(s) : pp 31 - 39 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement du signal
[Termes IGN] humidité du sol
[Termes IGN] mesurage de phase
[Termes IGN] positionnement par GNSS
[Termes IGN] rapport signal sur bruit
[Termes IGN] récepteur GNSS
[Termes IGN] trajet multipleRésumé : (Editeur) [...] Although the FM "capture effect" provides some margin against multipath, it is not uncommon to lose stereo reception or to experience fading out of the signal while driving in built-up areas as a result of reflections. This same multipath phenomenon also affects GNSS signals. Unlike satellite TV antennas, the antennas feeding our GNSS receivers are omnidirectional. So we have the possibility of not only receiving a direct, line-of-sight signal from a GNSS satellite but also any indirect signal from the satellite that gets reflected off nearby buildings or other objects or even the ground. GNSS antenna and receiver manufacturers have developed techniques to minimize the impact of multipath on the GNSS observables. Nevertheless, there is typically some residual multipath afflicting the pseudorange and carrier-phase observables that limits the precision and accuracy of position determinations. Telltale signs of multipath are the quasi-periodic fluctuations in the signal-to-noise ratios (SNRs) reported by some GNSS receivers, and in this month's column, we learn how an analysis of SNR values can be used to map and better understand the multipath environment surrounding an antenna. And, although an annoyance for most GNSS users, it turns out that multipath is not all bad. By analyzing the SNR fluctuations due to multipath, characteristics of the reflector can be deduced. If the reflector is the ground, then the amount of moisture in the soil can be measured. GNSS for measuring soil moisture? Who would have thought? Copyright Questex Media Group Numéro de notice : A2009-448 Affiliation des auteurs : non IGN Thématique : IMAGERIE/POSITIONNEMENT Nature : Article DOI : sans Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=30079
in GPS world > vol 20 n° 10 (October 2009) . - pp 31 - 39[article]Exemplaires(1)
Code-barres Cote Support Localisation Section Disponibilité 067-09101 SL Revue Centre de documentation Revues en salle Disponible
Titre : Improving the precision and accuracy of geodetic GPS : applications to multipath and seismology Type de document : Thèse/HDR Auteurs : A. Bilich, Auteur ; K. Larson, Directeur de thèse Editeur : Boulder [Etats-Unis] : University of Colorado Année de publication : 2006 Importance : 374 p. Format : 21 x 28 cm ISBN/ISSN/EAN : 978-0-542-94205-1 Note générale : Bibliographie
A thesis submitted to the Faculty of the graduate school of the University of Colorado in partial fulfillment of the requirements for the degree of Doctor of philosophy, department of aerospace engineering sciencesLangues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale
[Termes IGN] égalisation
[Termes IGN] erreur de positionnement
[Termes IGN] filtrage du bruit
[Termes IGN] mesurage de phase
[Termes IGN] mesurage de pseudo-distance
[Termes IGN] positionnement par GPS
[Termes IGN] rapport signal sur bruit
[Termes IGN] réduction
[Termes IGN] séisme
[Termes IGN] sismologie
[Termes IGN] trajet multipleIndex. décimale : THESE Thèses et HDR Résumé : (Auteur) The Global Positioning System (GPS) enables precise and accurate determination of position anywhere on anywhere on the Earth, a boon to the field of geodesy. Although great advances in geodetic GPS positioning precision and accuracy have been made over the last decade, improvements can still be made. This dissertation addresses GPS positioning error from two different directions---understanding and taking advantage of the repeating nature of some errors, or understanding and taking advantage of the relationship between errors in different contemporaneous GPS observables. In the area of high-rate GPS positioning, repeating errors have a substantial impact on the solution. In this dissertation, I study high-rate GPS error reduction using data from the 2002 Denali Fault earthquake. I apply the techniques of modified sidereal filtering and spatial filtering to positions from 25 GPS stations throughout northwestern North America, and I develop improvements to these methods such as data equalization and careful selection of sidereal filtering sites. Substantial reduction in noise magnitude is achieved through proper application of sidereal and spatial filters, and the resulting 'GPS seismograms' show excellent agreement to records from seismometers. Multipath, where GPS signals arrive by more than one path and thereby create a range error, can be understood through the GPS observables. Multipath effects on GPS carrier phase, pseudorange, and signal-to-noise ratio (SNR) measurements are different but linked by the same underlying principles. In this dissertation, I explain multipath effects on the GPS observables and define multipath in terms of conditions specific to geodetic GPS installations and receivers. I develop two approaches to multipath errors, both using SNR measurements---a graphical method for multipath assessment, and a computational method for multipath modeling and carrier phase error reduction. The graphical method shows great promise for understanding spatial and temporal variability in multipath errors, but provides no avenue for removing these errors. The theory behind SNR modeling is robust, but complicated to implement with geodetic GPS measurements of SNR. I discuss the difficulties inherent in SNR modeling and demonstrate how this technique is of limited utility for geodetic GPS even in the most simple of multipath environments. Note de contenu : 1 Introduction
1.1 Global Positioning System Background
1.2 GPS Observables
1.3 Position Estimation with GIPSY
1.3.1 Satellite Orbits
1.3.2 Earth and Observation Models
1.3.3 Removing Ionospheric Effects
1.3.4 Unmodeled Terms
1.3.5 Position Solution
2 Overview of High-Rate Positioning Research
2.1 Comparision of GPS and Seismologic Measurements
2.2 Previous Work in GPS Seismology
2.3 Case Study: 2002 November 3 Denali Fault Event
2.3.1 Denali Fault earthquake
2.3.2 GPS network and analysis
2.3.3 Error-reduction methodology
3 High-rate GPS Techniques
3.1 Sidereal Filtering
3.1.1 Orbital repeat period
3.1.2 Modified sidereal filtering (MSF) method
3.1.3 Variables in sidereal filtering process
3.2 Additional Data Analysis
3.2.1 Ambiguity resolution
3.2.2 Data editing
3.3 Spatial Filtering
3.3.1 Common-mode errors
3.3.2 Spatial filtering method
3.3.3 Spatial filtering sites
3.3.4 Role of the reference site and filter order
4 High-rate GPS Results and Discussion
4.1 Surface Waves Recorded by GPS
4.2 Positioning Noise
4.2.1 Noise floor of GPS receivers
4.2.2 Generalized noise in GPS positions
4.3 Comparison to Seismic Recordings
4.4 Summary and Conclusions
4.5 Future Work
5 Overview of Multipath Research
5.1 Previous Work
5.2 Research Motivation and Overview
6 Principles of Multipath and SNR
6.1 GPS Receiver Signal Tracking
6.2 Multipath Terminology
6.3 Multipath Effects on GPS Observables
6.3.1 Pseudorange multipath
6.3.2 Carrier phase multipath
6.3.3 Effect of multipath on SNR
6.4 Summary of Multipath Theory
7 Multipath Under Geodetic GPS Conditions
7.1 Multipath Geometry for the Geodetic Case
7.1.1 Multipath geometry and errors
7.1.2 Time-varying behavior of ø and SNR
7.1.3 Multipath geometry and periodicity
7.1.4 Resolvable multipath frequencies
7.1.5 Multipath phasor spin
7.1.6 Direct and multipath amplitudes
7.1.7 Summary
7.2 Geodetic GPS Receivers
7.2.1 Computation and reporting of SNR
7.2.2 Characteristics of geodetic GPS SNR
7.2.3 Correlation of SNR and pseudorange multipath
7.2.4 Conclusions
8 Multipath Assessment for Permanent GPS Stations
8.1 SNR Power Spectral Maps
8.1.1 Spectral power estimates
8.1.2 Representation of gridded spectral power
8.2 Examples of Power Spectral Maps
8.2.1 TASH: tall pillar
8.2.2 MKEA: reflections from angled surfaces
8.2.3 CHUR: variable topography
8.3 Discussion and Future Work
9 Estimation of SNR-based Multipath Corrections
9.1 Direct Signal Amplitude and SNR Due to Multipath
9.2 Signal Conditioning
9.3 Multipath Frequency Estimation Via Sliding-Window Fast Fourier Transform (SWFFT)
9.4 Amplitude and Multipath Phase Estimation Via Adaptive Least Squares (ALS)
9.5 Construction of SNR and Multipath Corrections
9.6 Simulations
10 Phase Multipath Mitigation for GPS Stations
10.1 Salar de Uyuni Experiment
10.1.1 Phase errors
10.1.2 Phase multipath corrections
10.1.3 Effect of corrections on residuals and positions
10.2 TASH/KIT3 Network
10.2.1 SNR data
10.2.2 Phase multipath corrections
10.2.3 Phase errors and corrections
10.3 Discussion and Future Work
11 ConclusionsNuméro de notice : 14325 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Thèse française Note de thèse : Thèse de doctorat : philosophy. department of aerospace engineering sciences : Boulder,University of Colorado : 2006 nature-HAL : Thèse DOI : sans Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=45244 Exemplaires(1)
Code-barres Cote Support Localisation Section Disponibilité 14325-01 THESE Livre Centre de documentation Thèses Disponible
Titre : Current status of the doris pilot experiment and the future international doris service Type de document : Article/Communication Auteurs : Gilles Tavernier, Auteur ; Laurent Soudarin, Auteur ; K. Larson, Auteur ; Carey E. Noll, Auteur ; John Ries, Auteur ; Pascal Willis Année de publication : 2002 Article en page(s) : pp 151 - 156 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux
[Termes IGN] données DORIS
[Termes IGN] International DORIS ServiceRésumé : (auteur) The aim of the DORIS Pilot Experiment is to assess the need and feasibility of an International DORIS Service. A Call for Proposals was broadcasted in September 1999 to prompt qualified organizations to submit proposals for components of the future IDS. DORIS Days were held in Toulouse (May 2–3, 2000). This second version of these Doris days was in particular devoted to a review of the start-up of the Doris Pilot Experiment. This paper recalls the objectives of the future IDS, points out its components and structure, and gives information on the current and future activities. Numéro de notice : A2002-403 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/S0273-1177(02)00279-X Date de publication en ligne : 22/08/2002 En ligne : https://doi.org/10.1016/S0273-1177(02)00279-X Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=102909
in Advances in space research > vol 30 n° 2 (July 2002) . - pp 151 - 156[article]
