| 1. |
- Hickler, Thomas, et al.
(författare)
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Precipitation controls Sahel greening trend
- 2005
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Ingår i: Geophysical Research Letters. - 1944-8007. ; 32:21
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Tidskriftsartikel (refereegranskat)abstract
- The Sahel region has been identified as a "hot spot'' of global environmental change, but understanding of the roles of different climatic and anthropogenic forcing factors driving change in the region is incomplete. We show that a process-based ecosystem model driven by climatic and atmospheric CO2 data alone closely reproduces the satellite-observed greening trend of the Sahel vegetation and its interannual variability between 1982 and 1998. Changes in precipitation were identified as the primary driver of the aggregated simulated vegetation changes. According to the model, the increasing carbon uptake through vegetation was associated with an increasing relative carbon sink; but integrated over the whole period, the Sahel was predicted to be a net source of carbon.
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| 2. |
- Moberg, Christina, et al.
(författare)
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De unga gör helt rätt när de stämmer staten
- 2022
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Ingår i: Aftonbladet. - 1103-9000.
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- 1 620 forskare och lärare i forskarvärlden: Vi ställer oss bakom Auroras klimatkrav
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| 3. |
- Eklundh, Lars, et al.
(författare)
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Analysing vegetation changes in the Sahel using sensor data from Landsat and NOAA
- 2005
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Konferensbidrag (refereegranskat)abstract
- The semi-arid Sahel zone of Africa has suffered several periods of severe drought since about 1950. We have analyzed AVHRR Normalized Difference Vegetation Index (NDVI) over the Sahel for the period 1982-2002, and found extensive areas of increasing NDVI. To verify these changes we have analyzed Landsat TM and ETM+ scenes from 1984-1986 and 1999-2001 for areas in the Sudan, Central African Republic, Niger, Mali and Mauritania. Changes in the Landsat data were analysed by visual interpretation and change vector analysis. In areas of positive AVHRR NDVI change the analysis of Landsat data generally showed a transition from barren or sparse vegetation to a denser vegetation cover. Rainfall had increased over the course of time in several of these areas. In some areas visual interpretation indicated an expansion of agricultural land.
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| 4. |
- Eklundh, Lars, et al.
(författare)
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High resolution mapping of vegetation dynamics from Sentinel-2
- 2012
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Ingår i: Proceedings of 1st Sentinel-2 Preparatory Symposium. - 0379-6566. - 9789290922711 ; 707 SP
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Konferensbidrag (refereegranskat)abstract
- The aim of this work is to develop and test a method for generation of information on vegetation dynamics from high-spatial resolution data, such as Sentinel-2. In order to accomplish this, Sentinel-2 data were simulated from existing SPOT HRG and HRVIR scenes over Sweden. We used TIMESAT, a well-tested computer package for generating smooth seasonal profiles and generation of seasonality parameters, like start and end, length, amplitude, integrated values, seasonal maximum, derivatives, etc. The processing works on a pixel-by-pixel basis and is resistant to clouds and noise. Data gaps are handled, and quality information can be included to increase the fidelity of the fits. The pilot study demonstrated that TIMESAT was successful in fitting smooth model functions to the data, and generating seasonality parameters for the test area at 10 × 10 m resolution. We conclude that TIMESAT will be useful for generating vegetation dynamics data from high-spatial resolution data such as Sentinel-2. The smooth seasonal profiles will be extremely useful for driving high-resolution biophysical vegetation models, and the seasonality parameters will be excellent for change detection, and for studying trends in vegetation productivity and seasonality.
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| 5. |
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| 6. |
- Sjöström, Martin, et al.
(författare)
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Evaluation of satellite based indices for gross primary production estimates in a sparse savanna in the Sudan
- 2009
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4189. ; 6:1, s. 129-138
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Tidskriftsartikel (refereegranskat)abstract
- One of the more frequently applied methods for integrating controls on primary production through satellite data is the Light Use Efficiency (LUE) approach. Satellite indices such as the Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI) and the Shortwave Infrared Water Stress Index (SIWSI) have previously shown promise as predictors of primary production in several different environments. In this study, we evaluate NDVI, EVI and SIWSI derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite sensor against in-situ measurements from central Sudan in order to asses their applicability in LUE-based primary production modeling within a water limited environment. Results show a strong correlation between vegetation indices and gross primary production (GPP), demonstrating the significance of vegetation indices for deriving information on primary production with relatively high accuracy at similar areas. Evaluation of SIWSI however, reveal that the fraction of vegetation apparently is to low for the index to provide accurate information on canopy water content, indicating that the use of SIWSI as a predictor of water stress in satellite data-driven primary production modeling in similar semi-arid ecosystems is limited.
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| 7. |
- Sjöström, Martin, et al.
(författare)
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Exploring the potential of MODIS EVI for modeling gross primary production across African ecosystems
- 2011
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Ingår i: Remote Sensing of Environment. - : Elsevier BV. - 0034-4257. ; 115:4, s. 1081-1089
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Tidskriftsartikel (refereegranskat)abstract
- One of the most frequently applied methods for integrating controls on primary production through satellite data is the light use efficiency (LUE) approach, which links vegetation gross or net primary productivity (GPP or NPP) to remotely-sensed estimates of absorbed photosynthetically active radiation (APAR). Eddy covariance towers provide continuous measurements of carbon flux, presenting an opportunity for evaluation of satellite estimates of GPP. Here we investigate relationships between eddy covariance estimated GPP, environmental variables and the enhanced vegetation index (EVI) from the Moderate Resolution Imaging Spectroradiometer (MODIS) across African savanna ecosystems. EVI was found to correlate well with estimated GPP on a site-by-site basis. Combining EVI with tower-measured PAR and evaporative fraction (EF, a measure of water sufficiency) improved the direct relationship between GPP and EVI at the majority of the sites. The slope of this relationship was strongly related to site peak leaf area index (LAI). These results are promising for the extension of GPP through the use of remote sensing data to a regional or even continental scale.
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