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Titre : Lidar waveform modeling using a marked point process Type de document : Article/Communication Auteurs : Clément Mallet , Auteur ; Florent Lafarge, Auteur ; Uwe Soergel, Auteur ; Christian Heipke, Auteur ; Frédéric Bretar, Auteur Editeur : New York : Institute of Electrical and Electronics Engineers IEEE Année de publication : 07/11/2009 Conférence : ICIP 2009, 16th IEEE International Conference on Image Processing 07/11/2009 10/11/2009 Le Caire Egypte Proceedings IEEE Importance : 4 p. Format : 21 x 30 cm Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement du signal
[Termes IGN] algorithme du recuit simulé
[Termes IGN] chaîne de Markov
[Termes IGN] données localisées 3D
[Termes IGN] forme d'onde
[Termes IGN] lasergrammétrie
[Termes IGN] méthode de Monte-Carlo
[Termes IGN] milieu urbain
[Termes IGN] processus ponctuel marqué
[Termes IGN] reconstruction du signal
[Termes IGN] semis de points
[Termes IGN] signal laser
[Termes IGN] signal lidarRésumé : (Auteur) Lidar waveforms are 1D signal consisting of a train of echoes where each of them correspond to a scattering target of the Earth surface. Modeling these echoes with the appropriate parametric function is necessary to retrieve physical information about these objects and characterize their properties. This paper presents a marked point process based model to reconstruct a lidar signal in terms of a set of parametric functions. The model takes into account both a data term which measures the coherence between the models and the waveforms, and a regularizing term which introduces physical knowledge on the reconstructed signal. We search for the best configuration of functions by performing a Reversible Jump Markov Chain Monte Carlo sampler coupled with a simulated annealing. Results are finally presented on different kinds of signals in urban areas. Numéro de notice : C2009-048 Affiliation des auteurs : MATIS+Ext (1993-2011) Thématique : IMAGERIE/POSITIONNEMENT Nature : Communication nature-HAL : ComAvecCL&ActesPubliésIntl DOI : 10.1109/ICIP.2009.5413380 En ligne : https://doi.org/10.1109/ICIP.2009.5413380 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=64296 Documents numériques
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Lidar waveform modeling ... - pdf auteurAdobe Acrobat PDF It's not all bad, understanding and using GNSS multipath / A. Bilich in GPS world, vol 20 n° 10 (October 2009)
[article]
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]Réservation
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Code-barres Cote Support Localisation Section Disponibilité 067-09101 SL Revue Centre de documentation Revues en salle Disponible The WAAS L5 signal: an assessment of its behavior and potential end use / H. Rho in GPS world, vol 20 n° 5 (May 2009)
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Titre : The WAAS L5 signal: an assessment of its behavior and potential end use Type de document : Article/Communication Auteurs : H. Rho, Auteur ; R.B. Langley, Auteur Année de publication : 2009 Article en page(s) : pp 42 - 48 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement du signal
[Termes IGN] signal GPS
[Termes IGN] signal multidimensionnel
[Termes IGN] test de performance
[Termes IGN] Wide Area Augmentation SystemRésumé : (Auteur) The recent launch of the GPS Block IIR-20(M) satellite and the commissioning of its L5 demonstration payload herald the beginning of a bright new era in space-based positioning, navigation, and timing. The new satellite signal is anticipated to provide better-quality range measurements and possibly improve the tracking performance of a GPS receiver compared with current civil L1 and L2 signals through use of improved signal structures. The L5 signal will be standard on the future Block IIF and Block III satellites.
However, some readers may be surprised to learn that L5 signals have been continuously transmitted by a pair of satellites for the past several years. The geostationary Earth-orbiting (GEO) satellites used by the U.S. Federal Aviation Administration's (FAA's) Wide Area Augmentation System to provide enhanced integrity and accuracy include not only an L1 payload but an L5 payload as well. While the WAAS L5 signals have been broadcast from space for some time, they did not come from a satellite in medium Earth orbit, and so it was necessary to include the demonstration payload on the GPS Block IIR-20(M) satellite to guarantee the L5 frequency filing with the International Telecommunication Union.
There are some differences between the WAAS L5 signals and the future fully fledged GPS L5 signals. The WAAS L5 signals only use a single-channel carrier (there is no quadrature or Q channel) and the data rate is 250 bits per second (bps) rather than 50 bps. The WAAS signals are actually generated on the ground and relayed through the GEOs using a "bent pipe" approach. The FAA uses the L5 signals, in conjunction with the L1 signals, to compute ionospheric delays as part of the closed-loop control of the broadcast signals.
Although the WAAS L5 signals are not yet intended for end users, can they be used now for positioning and navigation and, if so, are there any caveats? In this month's column, I am joined by one of my graduate students, Hyun-ho Rho, who has looked at the WAAS L5 transmissions, examining their signal strengths, multipath characteristics, and instrumental bias issues. Precise positioning performance of WAAS pseudoranges has also been assessed as an independent check on instrumental bias compensation by the WAAS control segment. The favorable results point to a future of the L5 signal, on both the WAAS satellites and the next-generation GPS satellites, which is bright indeed. Copyright Questex Media GroupNuméro de notice : A2009-178 Affiliation des auteurs : non IGN Thématique : IMAGERIE/POSITIONNEMENT Nature : Article DOI : sans Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=29808
in GPS world > vol 20 n° 5 (May 2009) . - pp 42 - 48[article]Réservation
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Code-barres Cote Support Localisation Section Disponibilité 067-09051 SL Revue Centre de documentation Revues en salle Disponible
contenu dans ISPRS Workshop Laserscanning'09, Paris, France, September 1-2, 2009 / Frédéric Bretar (2009)
Titre : A stochastic approach for modelling airborne lidar waveforms Type de document : Article/Communication Auteurs : Clément Mallet , Auteur ; Florent Lafarge, Auteur ; Michel Roux, Auteur ; Uwe Soergel, Auteur ; et al., Auteur Editeur : International Society for Photogrammetry and Remote Sensing ISPRS Année de publication : 2009 Collection : International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences, ISSN 1682-1750 num. 38-3/W8 Conférence : ISPRS 2009, Workshop LaserScanning 01/09/2009 02/09/2009 Paris France OA Archives proceedings Importance : pp 201 - 206 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement du signal
[Termes IGN] chaîne de Markov
[Termes IGN] données lidar
[Termes IGN] forme d'onde pleine
[Termes IGN] méthode de Monte-Carlo
[Termes IGN] milieu urbain
[Termes IGN] modèle stochastique
[Termes IGN] reconstruction du signal
[Termes IGN] signal laser
[Termes IGN] signal lidarRésumé : (Auteur) In contrast to conventional airborne multi-echo laser scanner systems, full-waveform (FW) lidar systems are able to record the entire emitted and backscattered signals of each laser pulse. Instead of clouds of individual 3D points, FW devices provide ID profiles of the 3D scene, which allows gaining additional and more detailed observations of the illuminated surfaces. Indeed, lidar waveforms are signals consisting of a train of echoes where each of them corresponds to a scattering target of the Earth surface or a group of close objects leading to superimposed signals. Modelling these echoes with the appropriate parametric function is necessary to retrieve physical information about these objects and characterize their properties. Henceforth, the extracted parameters can be useful for subsequent object segmentation and/or classification. This paper presents a stochastic based model to reconstruct lidar waveforms in terms of a set of parametric functions. The model takes into account both a data term which measures the coherence between the proposed configurations and the waveforms, and a regularizing term which introduces physical knowledge on the reconstructed signal. We search for the best configuration of functions by performing a Reversible Jump Markov Chain Monte Carlo sampler coupled with a stochastic relaxation. Finally, the algorithm is validated on waveforms from several airborne lidar sensors, showing the suitability of the approach even when the traditional assumption of Gaussian decomposition of waveforms is invalid. Numéro de notice : C2009-004 Affiliation des auteurs : MATIS+Ext (1993-2011) Thématique : IMAGERIE/POSITIONNEMENT Nature : Communication nature-HAL : ComAvecCL&ActesPubliésIntl DOI : sans En ligne : https://www.isprs.org/proceedings/XXXVIII/3-W8/papers/201_laserscanning09.pdf Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=65044 Interference heads-up: receiver techniques for detecting and characterizing RFI [radio-frequency interference] / P. Ward in GPS world, vol 19 n° 6 (June 2008)
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Titre : Interference heads-up: receiver techniques for detecting and characterizing RFI [radio-frequency interference] Type de document : Article/Communication Auteurs : P. Ward, Auteur Année de publication : 2008 Article en page(s) : pp 64 - 73 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement du signal
[Termes IGN] brouillage
[Termes IGN] interférence
[Termes IGN] rapport signal sur bruit
[Termes IGN] récepteur GNSSRésumé : (Editeur) As we all know, GPS signals are weak. At a receiver's antenna, in the open air, their strength is about-160 dBW or 1 x 10~l6watts. Compare this to a cell-phone signal, which might be 60 dBW or 1 x 10~6 watts, 10 billion times stronger! While code correlation in the receiver lifts the GPS signals above the background noise floor, the signals are still relatively fragile, and building walls and other obstructions can significantly attenuate the received signal power so that they cannot be tracked by a conventional receiver. It is the ratio of the signal power to the noise power per unit band-width that determines the trackability of | the signal. Accordingly, if the receiver's noise floor should increase sufficiently, even in an outdoor environment, the signals may also become untrackable. This can happen when the receiver is subjected to intentional or unintentional radio-frequency interference (RFI) by transmitter operating on or near GPS frequencies. If the interference is strong enough, it can jam the receiver. Although intentional jamming is typically of concern only to military GPS users, unintentional jamming can occur anywhere and any- time and can affect large numbers of users within the range of the jamming transmitter. The jamming incident in San Diego harbor in January 2007, for example, affected all GPS users within a range of about 15 kilometers including a medical services paging network. Such jamming renders a GPS receiver inoperable. But how do users know that their receivers are being jammed and not suffering some other type of malfunction? Clearly it would be advantageous for users to receive a heads-up when jamming signals are present and, if possible, for the receiver to take corrective action automatically. In this month's column, we look at some simple techniques, which can be easily incorporated into the design of a GNSS receiver, to detect, characterize, and actually mitigate RFI. Such receiver enhancements will benefit civilian and military users alike. Copyright Questex Media Group Inc Numéro de notice : A2008-165 Affiliation des auteurs : non IGN Thématique : IMAGERIE/POSITIONNEMENT Nature : Article DOI : sans Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=29160
in GPS world > vol 19 n° 6 (June 2008) . - pp 64 - 73[article]Réservation
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