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Uncertainties in tree cover maps of Sub-Saharan Africa and their implications for measuring progress towards CBD Aichi Targets / Dorit Gross in Remote sensing in ecology and conservation, vol 4 n° 2 (June 2018)    

Public [article]  inRemote sensing in ecology and conservation > vol 4 n° 2 (June 2018) Titre : Uncertainties in tree cover maps of Sub-Saharan Africa and their implications for measuring progress towards CBD Aichi Targets Type de document : Article/Communication Auteurs : Dorit Gross, Auteur ; Frédéric Achard, Auteur ; Grégoire Dubois, Auteur ; Andreas Brink, Auteur ; Herbert H.T. Prins, Auteur Année de publication : 2018 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de télédétection [Termes IGN] Afrique subsaharienne [Termes IGN] analyse diachronique [Termes IGN] carte forestière [Termes IGN] habitat (nature) [Termes IGN] image Landsat-ETM+ [Termes IGN] image Landsat-TM [Termes IGN] image Terra-MODIS [Termes IGN] incertitude géométrique [Termes IGN] politique de conservation (biodiversité) Résumé : (auteur) The growing access to Earth Observations and processing capabilities have stimulated the production of global and regional products that are commonly used to assess tree-covered habitats and their changes. The popularity of these products has led to their use for defining baselines and to assess progress in conserving natural habitats, in particular, in the context of the conservation targets to 2020 set by the UN Convention on Biological Diversity. In this paper, we reviewed three tree cover products commonly used over Sub-Saharan Africa: (1) MODIS Vegetation Continuous Field percent tree cover map, (2) Global Forest Change map and (3) TREES product. Over a systematic sample of 2045 map subsets, each having a size of 10 × 10 km², we calculated the extent and change of tree cover from each product for the period between 2000 and 2010. Our statistical and spatial comparison shows noticeable discrepancies between the three products, which lead to uncertainties when assessing tree cover across varying ecosystems. These differences are highest in habitats where tree cover is fragmented or reaches medium density levels and overlap with areas of high economic development potential, where habitat changes are likely to occur in the near future. We discuss these findings in the context of using these remotely sensed tree cover products to support current global biodiversity conservation policies. Numéro de notice : A2018-004 Affiliation des auteurs : non IGN Thématique : FORET/IMAGERIE Nature : Article DOI : 10.1002/rse2.52 En ligne : https://doi.org/10.1002/rse2.52 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=88737 [article]

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Continuum removed band depth analysis for detecting the effects of natural gas, methane and ethane reflectance / M.F. Noomen in Remote sensing of environment, vol 105 n° 3 (15/12/2006)  

Public [article]  inRemote sensing of environment > vol 105 n° 3 (15/12/2006) . - pp 262 - 270 Titre : Continuum removed band depth analysis for detecting the effects of natural gas, methane and ethane reflectance Type de document : Article/Communication Auteurs : M.F. Noomen, Auteur ; Andrew K. Skidmore, Auteur ; Freek Van Der Meer, Auteur ; Herbert H.T. Prins, Auteur Année de publication : 2006 Article en page(s) : pp 262 - 270 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de télédétection [Termes IGN] bande visible [Termes IGN] gaz naturel [Termes IGN] photosynthèse [Termes IGN] réflectance végétale [Termes IGN] santé [Termes IGN] spectrophotométrie [Termes IGN] végétation Résumé : (Auteur) It is known that natural gas in the soil affects vegetation health, which may be detected through analysis of reflectance spectra. Since natural gas is invisible, changes in the vegetation could potentially indicate gas leakage. Although it is known that gas in soil affects plant reflectance, the relationship between natural gas and the development and reflectance properties of plants has not been studied. The objective of this study was to test whether natural gas and its two main components, methane and ethane, affect vegetation reflectance in the chlorophyll and water absorption regions. An experiment was carried out in which maize (Zea mays) plants were grown in pots that were flushed with 10 l of gas per day for 39 + 4 days. Leaf reflectance was measured once a week with a spectrophotometer. The reflectance was analysed using continuum removal of the blue (400–550 nm), red (550–750 nm) and two water absorption features (1370–1570 nm and 1870–2170 nm), after which the band depths and normalized band depths were analyzed for each treatment. The band depth analysis showed that ethane caused an initial increase of 10% in reflectance between 560 and 590 nm, followed by a decrease during the course of the experiment. Normalized band depth analysis showed that ethane caused a reflectance shift of 1 to 5 nm towards longer wavelengths compared to the control reflectance in the visible region. All gases caused an increase in reflectance in the water absorption bands. The physiological reflectance index, PRI, which has previously linked water stress to photosynthetic activity, suggested that the hydrocarbon gases (particularly ethane) decreased the photosynthetic activity of the plants. The combination of reduced band depths in the chlorophyll and water absorption regions and the increased PRI suggests that ethane gas in the soil hampered a normal water uptake by maize plants in an early stage of their growth. Although further research is necessary to upscale the results from the laboratory to the field, the increased reflectance in the 560–590 nm region caused by ethane together with the increased PRI are promising indicators for gas leakage. Copyright Elsevier Numéro de notice : A2006-558 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.rse.2006.07.009 En ligne : https://doi.org/10.1016/j.rse.2006.07.009 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=28281 [article]

Predicting in situ pasture quality in the Kruger National Park, South Africa, using continuum-removed absorption features / Onisimo Mutanga in Remote sensing of environment, vol 89 n° 3 (15/02/2004)  

Public [article]  inRemote sensing of environment > vol 89 n° 3 (15/02/2004) . - pp 393 - 408 Titre : Predicting in situ pasture quality in the Kruger National Park, South Africa, using continuum-removed absorption features Type de document : Article/Communication Auteurs : Onisimo Mutanga, Auteur ; Andrew K. Skidmore, Auteur ; Herbert H.T. Prins, Auteur Année de publication : 2004 Article en page(s) : pp 393 - 408 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement d'image optique [Termes IGN] Afrique du sud (état) [Termes IGN] azote [Termes IGN] biochimie [Termes IGN] carbone [Termes IGN] forêt tropicale [Termes IGN] image hyperspectrale [Termes IGN] parc naturel national [Termes IGN] paturage [Termes IGN] phosphore [Termes IGN] potassium [Termes IGN] prairie [Termes IGN] réflectance végétale [Termes IGN] régression linéaire [Termes IGN] savane [Termes IGN] spectroradiomètre [Termes IGN] zone intertropicale Résumé : (Auteur) The remote sensing of pasture quality as determined by nitrogen, phosphorous, potassium, calcium and magnesium concentration is critical for a better understanding of wildlife and livestock feeding patterns. Although remote sensing techniques have proved useful for assessing the concentration of foliar biochemicals under controlled laboratory conditions, more investigation is required to assess their capabilities in the field where inconsistent results have been obtained so far. We investigated the possibility of determining the concentration of in situ biochemicals in a savanna rangeland, using the spectral reflectance of five grass species. Canopy spectral measurements were taken in the field using a GER 3700 spectroradiometer. We tested the utility of using four variables derived from continuum-removed absorption features for predicting canopy nitrogen, phosphorous, potassium, calcium and magnesium concentration: (i) continuum-removed derivative reflectance (CRDR), (ii) band depth (BD), (iii) band depth ratio (BDR) and (iv) normalised band depth index (NBDI). Stepwise linear regression was used to select wavelengths from the absorption-feature-based variables. Univariate correlation analysis was also done between the first derivative reflectance and biochemicals. Using a training data set, the variables derived from continuum-removed absorption features could predict biochemicals with R2 values ranging from 0.43 to 0.80. Results were highest using CRDR data, which yielded R2 values of 0.70, 0.80, 0.64, 0.50 and 0.68 with root mean square errors (RMSE) of 0.01, 0.004, 0.03, 0.01 and 0.004 for nitrogen, phosphorous, potassium, calcium and magnesium, respectively. Predicting biochemicals on a test data set, using regression models developed from a training data set. resulted in R2 values ranging from 0. 15 to 0.70. The error of prediction (RSE) in the test data set was 0.08 (+ 10.25% of mean), 0.05 (+ 5.2% of mean), 0.02 (+ 11.11% of mean), 0.05 (+ 11.6% of mean) and 0.03 (+ 15% of mean) for nitrogen, potassium, phosphorous. calcium and magnesium, respectively, using CRDR. When data was partitioned into species groups, the R2 increased significantly to >0.80. With high-quality radiometric and geometric calibration of hyperspectral imagery, the techniques applied in this study (i.e. continuum removal on absorption features) may also be applied on data acquired by airborne and spacebome imaging spectrometers to predict and ultimateIy to map the concentration of macronutrients in tropical rangelands. Numéro de notice : A2004-020 Affiliation des auteurs : non IGN Thématique : FORET/IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.rse.2003.11.001 En ligne : https://doi.org/10.1016/j.rse.2003.11.001 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=26548 [article]