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GPS receiver phase biases estimable in PPP-RTK networks : dynamic characterization and impact analysis / Baocheng Zhang in Journal of geodesy, vol 92 n° 6 (June 2018)  

Public [article]  inJournal of geodesy > vol 92 n° 6 (June 2018) . - pp 659 – 674 Titre : GPS receiver phase biases estimable in PPP-RTK networks : dynamic characterization and impact analysis Type de document : Article/Communication Auteurs : Baocheng Zhang, Auteur ; Teng Liu, Auteur ; Yunbin Yuan, Auteur Année de publication : 2018 Article en page(s) : pp 659 – 674 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Navigation et positionnement [Termes IGN] caractérisation [Termes IGN] données GPS [Termes IGN] erreur systématique [Termes IGN] filtre de Kalman [Termes IGN] filtre passe-bas [Termes IGN] GPS en mode cinématique [Termes IGN] impact sur les données [Termes IGN] phase GPS [Termes IGN] positionnement cinématique en temps réel [Termes IGN] positionnement ponctuel précis [Termes IGN] récepteur bifréquence Résumé : (Auteur) The integer ambiguity resolution enabled precise point positioning (PPP-RTK) has been proven advantageous in a wide range of applications. The realization of PPP-RTK concerns the isolation of satellite phase biases (SPBs) and other corrections from a network of Global Positioning System (GPS) reference receivers. This is generally based on Kalman filter in order to achieve real-time capability, in which proper modeling of the dynamics of various types of unknowns remains crucial. This paper seeks to gain insight into how to reasonably deal with the dynamic behavior of the estimable receiver phase biases (RPBs). Using dual-frequency GPS data collected at six colocated receivers over days 50–120 of 2015, we analyze the 30-s epoch-by-epoch estimates of L1 and wide-lane (WL) RPBs for each receiver pair. The dynamics observed in these estimates are a combined effect of three factors, namely the random measurement noise, the multipath and the ambient temperature. The first factor can be overcome by turning to a real-time filter and the second by considering the use of a sidereal filtering. The third factor has an effect only on the WL, and this effect appears to be linear. After accounting for these three factors, the low-pass-filtered, sidereal-filtered, epoch-by-epoch estimates of L1 RPBs follow a random walk process, whereas those of WL RPBs are constant over time. Properly modeling the dynamics of RPBs is vital, as it ensures the best convergence of the Kalman-filtered, between-satellite single-differenced SPB estimates to their correct values and, in turn, shortens the time-to-first-fix at user side. Numéro de notice : A2018-151 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-017-1085-z Date de publication en ligne : 13/11/2017 En ligne : https://doi.org/10.1007/s00190-017-1085-z Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=89764 [article]

An assessment of algorithmic parameters affecting image classification accuracy by random forests / Dee Shi in Photogrammetric Engineering & Remote Sensing, PERS, vol 82 n° 6 (June 2016)  

Public [article]  inPhotogrammetric Engineering & Remote Sensing, PERS > vol 82 n° 6 (June 2016) . - pp 407 - 417 Titre : An assessment of algorithmic parameters affecting image classification accuracy by random forests Type de document : Article/Communication Auteurs : Dee Shi, Auteur ; Xiaojun Yang, Auteur Année de publication : 2016 Article en page(s) : pp 407 - 417 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement d'image optique [Termes IGN] algorithme d'apprentissage [Termes IGN] classification [Termes IGN] classification par forêts d'arbres décisionnels [Termes IGN] impact sur les données [Termes IGN] occupation du sol [Termes IGN] précision de la classification Résumé : (Auteur) Random forests as a promising ensemble learning algorithm have been increasingly used for remote sensor image classification, and are found to perform identical or better than some popular classifiers. With only two algorithmic parameters, they are relatively easier to implement. Existing literature suggests that the performance of random forests is insensitive to changing algorithmic parameters. However, this was largely based on the classifier's accuracy that does not necessarily represent the resulting thematic map accuracy. The current study extends beyond the classifier's accuracy assessment and investigate how the algorithmic parameters could affect the resulting thematic map accuracy by random forests. A set of random forest models with different parameter settings was carefully constructed and then used to classify a satellite image into multiple land cover categories. Both the classifier's accuracy and the map accuracy were assessed. The results reveal that these parameters can affect the map accuracy up to 9 ∼16 percent for some classes, although their impact on the classifier's accuracy was quite limited. A careful parameterization prioritizing thematic map accuracy can help improve the performance of random forests in image classification, especially for spectrally complex land cover classes. These findings can help establish practical guidance on the use of random forests in the remote sensing community. Numéro de notice : A2016-440 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article DOI : 10.14358/PERS.82.6.407 En ligne : http://dx.doi.org/10.14358/PERS.82.6.407 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=81345 [article]

Analysis of star camera errors in GRACE data and their impact on monthly gravity field models / Pedro Inácio in Journal of geodesy, vol 89 n° 6 (June 2015)  

Public [article]  inJournal of geodesy > vol 89 n° 6 (June 2015) . - pp 551 - 571 Titre : Analysis of star camera errors in GRACE data and their impact on monthly gravity field models Type de document : Article/Communication Auteurs : Pedro Inácio, Auteur ; Pavel Ditmar, Auteur ; Roland Klees, Auteur ; Hassan Hashemi Farahani, Auteur Année de publication : 2015 Article en page(s) : pp 551 - 571 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] acquisition de données [Termes IGN] analyse diachronique [Termes IGN] anomalie de pesanteur [Termes IGN] capteur spatial [Termes IGN] champ de pesanteur terrestre [Termes IGN] données GRACE [Termes IGN] erreur de mesure [Termes IGN] impact sur les données [Termes IGN] modèle d'erreur [Termes IGN] orientation du capteur [Termes IGN] propagation d'erreur Résumé : (auteur) Star cameras (SCs) on board the GRACE satellites provide information about the attitudes of the spacecrafts. This information is needed to reduce the K-band ranging data to the centre of mass of the satellites. In this paper, we analyse GRACE SC errors using two months of real data of the primary and secondary SCs. We show that the errors consist of a harmonic component, which is highly correlated with the satellite’s true anomaly, and a stochastic component. We built models of both error components, and use these models for error propagation studies. Firstly, we analyse the propagation of SC errors into inter-satellite accelerations. A spectral analysis reveals that the stochastic component exceeds the harmonic component, except in the 3–10 mHz frequency band. In this band, which contains most of the geophysically relevant signal, the harmonic error component is larger than the random component. Secondly, we propagate SC errors into optimally filtered monthly mass anomaly maps and compare them with the total error. We found that SC errors account for about 18 % of the total error. Moreover, gaps in the SC data series amplify the effect of SC errors by a factor of 5. Finally, an analysis of inter-satellite pointing angles for GRACE data between 2003 and 2010 reveals that inter-satellite ranging errors were exceptionally large during the period February 2003 till May 2003. During these months, SC noise is amplified by a factor of 3 and is a considerable source of errors in monthly GRACE mass anomaly maps. In the context of future satellite gravity missions, the noise models developed in this paper may be valuable for mission performance studies. Numéro de notice : A2015-350 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-015-0797-1 Date de publication en ligne : 03/03/2015 En ligne : https://doi.org/10.1007/s00190-015-0797-1 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=76724 [article]

Assessing the effect of snow/water obstructions on the measurement of tree seedlings in a large-scale temperate forest inventory / C. W. Woodall in Forestry, an international journal of forest research, vol 86 n° 4 (October 2013)  

Public [article]  inForestry, an international journal of forest research > vol 86 n° 4 (October 2013) . - pp 421 - 427 Titre : Assessing the effect of snow/water obstructions on the measurement of tree seedlings in a large-scale temperate forest inventory Type de document : Article/Communication Auteurs : C. W. Woodall, Auteur ; James A. Westfall, Auteur ; et al., Auteur Année de publication : 2013 Article en page(s) : pp 421 - 427 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Termes IGN] Etats-Unis [Termes IGN] forêt tempérée [Termes IGN] impact sur les données [Termes IGN] inventaire forestier étranger (données) [Termes IGN] neige [Vedettes matières IGN] Inventaire forestier Résumé : (auteur) National-scale forest inventories have endeavoured to include holistic measurements of forest health inclusive of attributes such as downed dead wood and tree regeneration that occur in the forest understory. Inventories may require year-round measurement of inventory plots with some of these measurements being affected by seasonal obstructions (e.g. snowpacks and seasonal flooding). In order to assess the potential effects that snow/water obstructions may have on the measurement/analysis of forest seedlings across large scales, the differences in seedling abundance between two inventory measurements (∼5-year remeasurement period) and as affected by snow/water depth was ascertained using a repeated forest inventory across the eastern US. Results indicate that there is a general trend of decreasing seedling density over time (−33.16 seedlings ha−1 year−1) in the eastern US, with snow/water depths in excess of 15 cm significantly affecting resulting estimates of seedling abundance. Although snow/water obstruction to seedling measurement occurred on ∼9 per cent of inventory plots across the eastern US, snow was a much more common situation occurring on nearly 50 per cent of plots (at time 1, 2 or both) at high latitudes (>45°). Given the statistically significant effect of snow/water on seedling abundance estimates, tree regeneration assessments should not include observations obstructed by snow/water depths that exceed minimum seedling heights. Furthermore, seedling abundance inventories may mitigate the influence of measurement obstructions by sampling only during the summer or incorporating climate information into their sampling logistics. Numéro de notice : A2013-788 Affiliation des auteurs : non IGN Thématique : FORET Nature : Article DOI : 10.1093/forestry/cpt013 En ligne : https://doi.org/10.1093/forestry/cpt013 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=78312 [article]

Space weather and the Australian ionospheric prediction service: ready for the Solar Max 2012 / Dave Neudegg in Space research today, n° 184 (01/08/2012)

Public [article]  inSpace research today > n° 184 (01/08/2012) . - pp 16 - 24 Titre : Space weather and the Australian ionospheric prediction service: ready for the Solar Max 2012 Type de document : Article/Communication Auteurs : Dave Neudegg, Auteur Année de publication : 2012 Article en page(s) : pp 16 - 24 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] atmosphère terrestre [Termes IGN] Australie [Termes IGN] impact sur les données [Termes IGN] propagation ionosphérique [Termes IGN] signal GNSS [Termes IGN] surveillance Résumé : (Auteur) [Introduction] The Ionospheric Prediction Service (IPS) is the "Radio and Space services" branch of the bureau of meteorology. IPS monitors the solar-terrestrial space environment to predict its varaibility and effect on technological systems. Numéro de notice : A2012-692 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=32138 [article]

Evaluation of the impact of atmospheric pressure loading modeling on GNSS data analysis / Rolf Dach in Journal of geodesy, vol 85 n° 2 (February 2011)  

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An evaluation of the impact of cartographic generalisation on length measurement computed from linear vector databases / Jean-François Girres (2011)  

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Inépuisable INSPIRE / Françoise de Blomac in SIG la lettre, n° 107 (mai 2009)

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Développements de grandes déviations pour des sommes pondérées appliqués à un problème géographique / Olivier Bonin (2005)    

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