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A digital camera as a tool to measure colour indices and related properties of sandy soils in semi-arid environments / N. Levin in International Journal of Remote Sensing IJRS, vol 26 n° 24 (December 2005)  

Public [article]  inInternational Journal of Remote Sensing IJRS > vol 26 n° 24 (December 2005) . - pp 5475 - 5492 Titre : A digital camera as a tool to measure colour indices and related properties of sandy soils in semi-arid environments Type de document : Article/Communication Auteurs : N. Levin, Auteur ; Eyal Ben-Dor, Auteur ; A. Singer, Auteur Année de publication : 2005 Article en page(s) : pp 5475 - 5492 Note générale : Bibliographie Langues : Français (fre) Descripteur : [Vedettes matières IGN] Applications de télédétection [Termes IGN] analyse comparative [Termes IGN] caméra numérique [Termes IGN] composition chimique [Termes IGN] couleur du sol [Termes IGN] étalonnage des données [Termes IGN] fer [Termes IGN] image RVB [Termes IGN] particule [Termes IGN] sable [Termes IGN] spectromètre [Termes IGN] zone semi-aride Résumé : (Auteur) Soil colour carries important information regarding the soil's chemical and physical properties. However, common practices for measuring soil colour, either by Munsell charts or by field/laboratory spectrometers, are insufficient, due to the subjective and nonquantitative character of the Munsell charts, and to the high cost and inconvenience of field spectrometers. We present herein, a method to characterize the colour of soil samples, and related chemical and physical properties of the soil, using a digital camera, and an array of coloured plastic chips, that are used for calibration purposes. Using 370 samples of sandy soils, we have demonstrated that both RGB values from digital images and their derived soil indices, correlate highly with similar measurements performed by a field spectrometer. When checked against free iron oxide content and against the percentage of fine particles in a subsample set of 42 soils, the redness index as measured by the digital camera gave similar or better correlations than those obtained from a field spectrometer, against both free iron oxides and fine particle contents (R2 of 89% for the iron oxides, and of for the fine particles). We propose the use of a digital camera as a field analytical tool to determine precisely: soil colour, iron oxide and fine particle content. Further study in this direction, with other soil population and more soil properties, is strongly advised in order to launch this as a vastly applicable and generic method. Numéro de notice : A2005-522 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1080/01431160500099444 En ligne : https://doi.org/10.1080/01431160500099444 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=27658 [article]

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Topographic information of sand dunes as extracted from shading effects using Landsat images / N. Levin in Remote sensing of environment, vol 90 n° 2 (30/03/2004)  

Public [article]  inRemote sensing of environment > vol 90 n° 2 (30/03/2004) . - pp 190 - 209 Titre : Topographic information of sand dunes as extracted from shading effects using Landsat images Type de document : Article/Communication Auteurs : N. Levin, Auteur ; Eyal Ben-Dor, Auteur ; A. Karnieli, Auteur Année de publication : 2004 Article en page(s) : pp 190 - 209 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Photogrammétrie numérique [Termes IGN] analyse comparative [Termes IGN] angle azimutal [Termes IGN] appariement d'histogramme [Termes IGN] dénivelée [Termes IGN] distribution du coefficient de réflexion bidirectionnelle BRDF [Termes IGN] dune [Termes IGN] extraction du relief [Termes IGN] image Landsat-ETM+ [Termes IGN] image Landsat-TM [Termes IGN] image multitemporelle [Termes IGN] image Terra-ASTER [Termes IGN] Israël [Termes IGN] ombre [Termes IGN] pente [Termes IGN] réflectance Résumé : (Auteur) Topographic variations affect the reflectance properties of the Earth's surface and are often removed in remote sensing studies. especially when significant terrain variations exist. In this study, however, we show that shading effects assessed by Landsat can be treated as a signal that stores important topographic information, especially when the spectral characteristics of a surface are homogenous. The coastal transverse dunes of the Ashdod area, and the desert linear dunes of Nizzana (both located in Israel), were selected to investigate the above-mentioned idea. The dune heights in these areas are 10 m on average (relative to their surroundings) and have maximum slopes of 33°. An innovative method for extracting slope, aspect, and height data for sand dunes using Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) images was developed, based on the regularity and periodicity of dunes landscapes. Using two Landsat images representing different sun zenith and azimuth angles, reflectance values of each image were converted to cos(i) values (i =incident angle between the surface normal and the solar beam radiation), applying histogram matching methods. The slope and aspect of each pixel were determined as those that give the best prediction of the observed value of cos(i). Height profiles were then extracted, using simple trigonometric relationships. The accuracies of heights and slopes along selected profile lines were to the order of 1 m and 3°, respectively (at a spatial resolution of 15 m). Best results were obtained when the images included one from the summer and the other from the winter, corresponding to maximum difference in solar zenith and azimuth angles. Errors in heights were attributed to surface heterogeneity (e.g., presence of biogenic soil crusts in the rainy season), geometric correction errors, cast shadows, and Bidirectional Reflectance Distribution Function (BRDF) effects. Comparison to Advanced Thermal Emission and Reflection Radiometer (ASTER) 3D information showed that the proposed method is better in representing the topographic variation of the area than the digital elevation model (DEM) produced by ASTER. Numéro de notice : A2004-141 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.rse.2003.12.008 En ligne : https://doi.org/10.1016/j.rse.2003.12.008 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=26668 [article]