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Complete and accurate data correction for seamless mosaicking of airborne hyperspectral images: A case study at a mining site in Inner Mongolia, China / Kun Tan in ISPRS Journal of photogrammetry and remote sensing, vol 165 (July 2020)  

Public [article]  inISPRS Journal of photogrammetry and remote sensing > vol 165 (July 2020) . - pp 1 - 15 Titre : Complete and accurate data correction for seamless mosaicking of airborne hyperspectral images: A case study at a mining site in Inner Mongolia, China Type de document : Article/Communication Auteurs : Kun Tan, Auteur ; Chao Niu, Auteur ; Xiuping Jia, Auteur ; et al., Auteur Année de publication : 2020 Article en page(s) : pp 1 - 15 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de télédétection [Termes IGN] atténuation [Termes IGN] correction atmosphérique [Termes IGN] distorsion du signal [Termes IGN] distribution du coefficient de réflexion bidirectionnelle BRDF [Termes IGN] image hyperspectrale [Termes IGN] mine [Termes IGN] Mongolie intérieure (Chine) [Termes IGN] mosaïquage d'images [Termes IGN] radiance [Termes IGN] rayonnement infrarouge [Termes IGN] réflectance de surface [Termes IGN] Short Waves InfraRed [Termes IGN] spectroradiométrie [Termes IGN] surveillance écologique Résumé : (auteur) Airborne hyperspectral remote sensing is an important application in the ecological monitoring of the environment in mining areas, and accurate preprocessing of the original images is the key to quantitative information retrieval. The original image data need radiation correction to acquire surface reflectance data. Due to the impact of the field angle, incidental radiance, and the bidirectional reflectance distribution function (BRDF), there can be a brightness gradient between adjacent strips, which leads to radiance difference and obvious chromatic aberration of the mosaicked images. We propose a novel data correction method for seamless mosaicking of airborne hyperspectral images. Firstly, visible and near-infrared (VNIR) and shortwave infrared (SWIR) sensors are calibrated in the laboratory, and the radiation calibration model of the sensor is established by an integrating-sphere system. A correction function is then established by combining the BRDF effect and the radiation attenuation coefficients. We also normalize the exposure time, sun altitude angle, and sensor altitude angle according to the flight strip. The results showed that this method is able to eliminate the signal distortion, allowing the seamless mosaicking of 37 strip images which were taken in different date and conditions in the study area. After the atmospheric correction of the imagery was completed, the accuracy of the preprocessing results was evaluated by field-measured ASD spectroradiometer data. The coefficient of determination R2 of the results for the reflectance was greater than 0.9. The experiments show that the proposed method has a good performance in radiation accuracy, and can provide high-quality hyperspectral data for the follow-up application of the ecological monitoring of a mining area. Numéro de notice : A2020-465 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.isprsjprs.2020.04.022 date de publication en ligne : 16/05/2020 En ligne : https://doi.org/10.1016/j.isprsjprs.2020.04.022 Format de la ressource électronique : url article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=95092 [article]

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FFT swept filtering: a bias-free method for processing fringe signals in absolute gravimeters / Petr Křen in Journal of geodesy, vol 93 n° 2 (February 2019)  

Public [article]  inJournal of geodesy > vol 93 n° 2 (February 2019) . - pp 219 - 227 Titre : FFT swept filtering: a bias-free method for processing fringe signals in absolute gravimeters Type de document : Article/Communication Auteurs : Petr Křen, Auteur ; Vojtech Pálinkáš, Auteur ; Pavel Mašika, Auteur ; Miloš Val’ko, Auteur Année de publication : 2019 Article en page(s) : pp 219 - 227 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] distorsion du signal [Termes IGN] erreur systématique [Termes IGN] filtre passe-bande [Termes IGN] gravimètre absolu [Termes IGN] pesanteur terrestre [Termes IGN] régression linéaire [Termes IGN] transformation rapide de Fourier Résumé : (auteur) Absolute gravimeters, based on laser interferometry, are widely used for many applications in geoscience and metrology. Although currently the most accurate FG5 and FG5X gravimeters declare standard uncertainties at the level of 2−3μGal, their inherent systematic errors affect the gravity reference determined by international key comparisons based predominately on the use of FG5-type instruments. The measurement results for FG5-215 and FG5X-251 clearly showed that the measured g-values depend on the size of the fringe signal and that this effect might be approximated by a linear regression with a slope of up to 0.030μGal/mV. However, these empirical results do not enable one to identify the source of the effect or to determine a reasonable reference fringe level for correcting g-values in an absolute sense. Therefore, both gravimeters were equipped with new measuring systems (according to Křen et al. in Metrologia 53:27–40, 2016. https://doi.org/10.1088/0026-1394/53/1/27 applied for FG5), running in parallel with the original systems. The new systems use an analogue-to-digital converter HS5 to digitize the fringe signal and a new method of fringe signal analysis based on FFT swept bandpass filtering. We demonstrate that the source of the fringe size effect is connected to a distortion of the fringe signal due to the electronic components used in the FG5(X) gravimeters. To obtain a bias-free g-value, the FFT swept method should be applied for the determination of zero-crossings. A comparison of g-values obtained from the new and the original systems clearly shows that the original system might be biased by approximately 3−5μGal due to improperly distorted fringe signal processing. Numéro de notice : A2019-079 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-018-1154-y date de publication en ligne : 19/05/2018 En ligne : https://doi.org/10.1007/s00190-018-1154-y Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=92197 [article]

Modeling canopy reflectance over sloping terrain based on path length correction / Gaofei Yin in IEEE Transactions on geoscience and remote sensing, vol 55 n° 8 (August 2017)  

Public [article]  inIEEE Transactions on geoscience and remote sensing > vol 55 n° 8 (August 2017) . - pp 4597 - 4609 Titre : Modeling canopy reflectance over sloping terrain based on path length correction Type de document : Article/Communication Auteurs : Gaofei Yin, Auteur ; Ainong Li, Auteur ; Wei Zhao, Auteur ; et al., Auteur Année de publication : 2017 Article en page(s) : pp 4597 - 4609 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de télédétection [Termes IGN] distorsion du signal [Termes IGN] figuré du terrain [Termes IGN] méthode de Monte-Carlo [Termes IGN] modèle de simulation [Termes IGN] modèle numérique de surface de la canopée [Termes IGN] montagne [Termes IGN] path length correction [Termes IGN] pente [Termes IGN] réflectance végétale Résumé : (Auteur) Sloping terrain induces distortion of canopy reflectance (CR), and the retrieval of biophysical variables from remote sensing data needs to account for topographic effects. We developed a 1-D model (the path length correction (PLC) based model) for simulating CR over sloping terrain. The effects of sloping terrain on single-order and diffuse scatterings are accounted for by PLC and modification of the fraction of incoming diffuse irradiance, respectively. The PLC model was validated via both Monte Carlo and remote sensing image simulations. The comparison with the Monte Carlo simulation revealed that the PLC model can capture the pattern of slope-induced reflectance distortion with high accuracy (red band: R2 = 0.88; root-mean-square error (RMSE) = 0.0045; relative RMSE (RRMSE) = 15%; near infrared response (NIR) band: R2 = 0.79; RMSE = 0.041; RRMSE = 16%). The comparison of the PLC-simulated results with remote sensing observations acquired by the Landsat8-OLI sensor revealed an accuracy similar to that with the Monte Carlo simulation (red band: R2 = 0.83; RMSE = 0.0053; RRMSE = 13%; NIR band: R2 = 0.77; RMSE = 0.023; RRMSE = 8%). To further validate the PLC model, we used it to implement topographic normalization; the results showed a large reduction in topographic effects after normalization, which implied that the PLC model captures reflectance variations caused by terrain. The PLC model provides a promising tool to improve the simulation of CR and the retrieval of biophysical variables over mountainous regions. Numéro de notice : A2017-500 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1109/TGRS.2017.2694483 En ligne : http://dx.doi.org/10.1109/TGRS.2017.2694483 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=86442 [article]

Investigations on the influence of antenna near-field effects and satellite obstruction on the uncertainty of GNSS-based distance measurements / Florian Zimmermann in Journal of applied geodesy, vol 10 n° 1 (March 2016)  

Public [article]  inJournal of applied geodesy > vol 10 n° 1 (March 2016) . - pp 53 - 60 Titre : Investigations on the influence of antenna near-field effects and satellite obstruction on the uncertainty of GNSS-based distance measurements Type de document : Article/Communication Auteurs : Florian Zimmermann, Auteur ; Christian Eling, Auteur ; Heiner Kuhlmann, Auteur Année de publication : 2016 Article en page(s) : pp 53 - 60 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Termes IGN] antenne GNSS [Termes IGN] distancemètre [Termes IGN] distorsion du signal [Termes IGN] double différence [Termes IGN] étalonnage d'instrument [Termes IGN] trajet multiple [Vedettes matières IGN] Traitement de données GNSS Résumé : (auteur) Antenna near-field effects are one of the accuracy limiting factors on GNSS-based distance measurements. In order to analyse these influences, a measurement campaign at an EDM calibration baseline site with optimum GNSS conditions was performed. To vary the distance between the antenna mount and the absolutely calibrated antennas, spacers with different lengths were used. Due to the comparison of the resulting GNSS-based distance measurements to a reference solution, the influences of the antenna near-field could be analyzed. The standard deviations of the differences to the reference solution, i. e., 0.31 mm for the distance and 0.46 mm for the height component, indicate that equal spacer and antenna combinations at both stations lead to a very high accuracy level. In contrast, different spacer and antenna combinations decrease the accuracy level. Thus, an identical set-up at both antenna stations and the usage of individually calibrated antennas minimize the near-field effects during the double-differencing process. Hence, these aspects can be identified as a prerequisite for highly accurate GNSS-measurements. In addition to near-field effects, the influence of satellite obstructions is investigated. Four realistic shadowing scenarios are numerically simulated on the basis of the observations, which were collected in the optimum surrounding of the EDM calibration baseline site. The comparison to nominal values indicates that a shadowing leads only to a slight decreasing of the accuracy. Consequently, there is a strong suspicion that multipath effects and signal distortions seem to have a greater influence on the accuracy of GNSS-based distance measurements than the satellite constellation. Numéro de notice : A2016-554 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article En ligne : http://dx.doi.org/10.1515/jag-2015-0026 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=81704 [article]

Antenna pilots UAV / Adrien Perkins in GPS world, vol 27 n° 2 (February 2016)

Public [article]  inGPS world > vol 27 n° 2 (February 2016) . - pp 48 - 56 Titre : Antenna pilots UAV Type de document : Article/Communication Auteurs : Adrien Perkins, Auteur ; Louis Dressel, Auteur ; Sherman Lo, Auteur ; Per Enge, Auteur Année de publication : 2016 Article en page(s) : pp 48 - 56 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Acquisition d'image(s) et de donnée(s) [Termes IGN] brouillage [Termes IGN] distorsion du signal [Termes IGN] drone [Termes IGN] navigation aérienne [Termes IGN] radiofréquence Résumé : (éditeur) A jammer hunting UAV employs a radio frequency (RF) detection system and a navigation control scheme. The RF detection component uses a directional antenna and the unmanned aerial vehicle’s (UAV’s) ability to rotate to determine a bearing to the jammer. The navigation control scheme selects a trajectory for making bearing measurements that enable rapid jammer localization, based on three bearing calculation methods: max, cross-correlation, and a modification of max leveraging the shape of the antenna’s main lobe, known as max3. Numéro de notice : A2016-032 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=79479 [article]

Ionospheric scintillations: How irregularities in electron density perturb satellite navigation systems / Satellite-based augmentation system ionospheric working group in GPS world, vol 23 n° 4 (April 2012)

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Aviation grade : New GPS signals, chips off the block IIF / R.E. Phelts in Inside GNSS, vol 5 n° 5 (July - August 2010) 

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