| 1. |
- Martínez, B., et al.
(author)
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Retrieval of daily gross primary production over Europe and Africa from an ensemble of SEVIRI/MSG products
- 2018
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In: International Journal of Applied Earth Observation and Geoinformation. - : Elsevier BV. - 1569-8432. ; 65, s. 124-136
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Journal article (peer-reviewed)abstract
- The main goal of this paper is to derive a method for a daily gross primary production (GPP) product over Europe and Africa taking the full advantage of the SEVIRI/MSG satellite products from the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) sensors delivered from the Satellite Application Facility for Land Surface Analysis (LSA SAF) system. Special attention is paid to model the daily GPP response from an optimized Montheith's light use efficiency model under dry conditions by controlling water shortage limitations from the actual evapotranspiration and the potential evapotranspiration (PET). The PET was parameterized using the mean daily air temperature at 2 m (Ta) from ERA-Interim data. The GPP product (MSG GPP) was produced for 2012 and assessed by direct site-level comparison with GPP from eddy covariance data (EC GPP). MSG GPP presents relative bias errors lower than 40% for the most forest vegetation types with a high agreement (r > 0.7) when compared with EC GPP. For drylands, MSG GPP reproduces the seasonal variations related to water limitation in a good agreement with site level GPP estimates (RMSE = 2.11 g m−2 day−1; MBE = −0.63 g m−2 day−1), especially for the dry season. A consistency analysis against other GPP satellite products (MOD17A2 and FLUXCOM) reveals a high consistency among products (RMSD < 1.5 g m−2 day−1) over Europe, North and South Africa. The major GPP disagreement arises over moist biomes in central Africa (RMSD > 3.0 g m−2 day−1) and over dry biomes with MSG GPP estimates lower than FLUXCOM (MBD up to −3.0 g m−2 day−1). This newly derived product has the potential for analysing spatial patterns and temporal dynamics of GPP at the MSG spatial resolutions on a daily basis allowing to better capture the GPP dynamics and magnitude.
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| 2. |
- Watts, J. D., et al.
(author)
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A satellite data driven biophysical modeling approach for estimating northern peatland and tundra CO2 and CH4 fluxes
- 2014
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In: Biogeosciences. - : Copernicus GmbH. - 1726-4189. ; 11:7, s. 1961-1980
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Journal article (peer-reviewed)abstract
- The northern terrestrial net ecosystem carbon balance (NECB) is contingent on inputs from vegetation gross primary productivity (GPP) to offset the ecosystem respiration (R-eco) of carbon dioxide (CO2) and methane (CH4) emissions, but an effective framework to monitor the regional Arctic NECB is lacking. We modified a terrestrial carbon flux (TCF) model developed for satellite remote sensing applications to evaluate wetland CO2 and CH4 fluxes over pan-Arctic eddy covariance (EC) flux tower sites. The TCF model estimates GPP, CO2 and CH4 emissions using in situ or remote sensing and reanalysis-based climate data as inputs. The TCF model simulations using in situ data explained >70% of the r(2) variability in the 8 day cumulative EC measured fluxes. Model simulations using coarser satellite (MODIS) and reanalysis (MERRA) Records accounted for approximately 69% and 75% of the respective r(2) variability in the tower CO2 and CH4 records, with corresponding RMSE uncertainties of <= 1.3 gCm(-2) d(-1) (CO2) and 18.2 mg Cm-2 d(-1) (CH4). Although the estimated annual CH4 emissions were small (<18 gCm(-2) yr(-1)) relative to R-eco (>180 gCm(-2) yr(-1)), they reduced the across-site NECB by 23% and contributed to a global warming potential of approximately 165 +/- 128 gCO(2)eqm(-2) yr(-1) when considered over a 100 year time span. This model evaluation indi-cates a strong potential for using the TCF model approach to document landscape-scale variability in CO2 and CH4 fluxes, and to estimate the NECB for northern peatland and tundra ecosystems.
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| 3. |
- Abdi, A. M., et al.
(author)
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First assessment of the plant phenology index (PPI) for estimating gross primary productivity in African semi-arid ecosystems
- 2019
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In: International Journal of Applied Earth Observation and Geoinformation. - : Elsevier BV. - 1569-8432. ; 78, s. 249-260
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Journal article (peer-reviewed)abstract
- The importance of semi-arid ecosystems in the global carbon cycle as sinks for CO 2 emissions has recently been highlighted. Africa is a carbon sink and nearly half its area comprises arid and semi-arid ecosystems. However, there are uncertainties regarding CO 2 fluxes for semi-arid ecosystems in Africa, particularly savannas and dry tropical woodlands. In order to improve on existing remote-sensing based methods for estimating carbon uptake across semi-arid Africa we applied and tested the recently developed plant phenology index (PPI). We developed a PPI-based model estimating gross primary productivity (GPP) that accounts for canopy water stress, and compared it against three other Earth observation-based GPP models: the temperature and greenness (T-G) model, the greenness and radiation (GöR) model and a light use efficiency model (MOD17). The models were evaluated against in situ data from four semi-arid sites in Africa with varying tree canopy cover (3–65%). Evaluation results from the four GPP models showed reasonable agreement with in situ GPP measured from eddy covariance flux towers (EC GPP) based on coefficient of variation (R 2 ), root-mean-square error (RMSE), and Bayesian information criterion (BIC). The GöR model produced R 2 = 0.73, RMSE = 1.45 g C m −2 d −1 , and BIC = 678; the T-G model produced R 2 = 0.68, RMSE = 1.57 g C m −2 d −1 , and BIC = 707; the MOD17 model produced R 2 = 0.49, RMSE = 1.98 g C m −2 d −1 , and BIC = 800. The PPI-based GPP model was able to capture the magnitude of EC GPP better than the other tested models (R 2 = 0.77, RMSE = 1.32 g C m −2 d −1 , and BIC = 631). These results show that a PPI-based GPP model is a promising tool for the estimation of GPP in the semi-arid ecosystems of Africa.
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| 4. |
- Laouali, D., et al.
(author)
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Source contributions in precipitation chemistry and analysis of atmospheric nitrogen deposition in a Sahelian dry savanna site in West Africa
- 2021
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In: Atmospheric Research. - : Elsevier BV. - 0169-8095. ; 251
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Journal article (peer-reviewed)abstract
- Experimental data on precipitation chemistry were collected at a semi-arid savanna in Senegal (Dahra) in 2013, 2014 and 2017. The chemical composition of precipitation was analyzed for inorganic and organic ions, using ionic chromatography. The pH values of precipitation range from 4.50 to 8.50 with 89% of the samples having basic pH. The composition of precipitation was controlled by four source contributions: marine, terrigenous, biogenic, and organic acids emissions from vegetation. The terrigenous contribution was the highest accounting for 42% of the total annual Volume Weighted Mean ionic concentrations, due to the proximity of the Saharan desert, followed by the marine source representing 36%, due to the location of Dahra close to the Atlantic Ocean. Nitrogenous (N) contribution represents 16% of the mean annual total ionic charge, from biogenic sources and livestock crossing the site all year round. Finally, the lowest contribution is from organic acidity (5%), due to the low density of vegetation especially during the dry season. Wet deposition fluxes in Dahra for all compounds show larger values than at other Sahelian savanna sites. Dry N deposition in Dahra was also estimated by inferential method using gas concentration measurements and modeled dry deposition velocities. The total N deposition fluxes (wet plus dry) range from 3.80 to 4.81 kgN ha−1 yr−1, comparable to fluxes at other semi-arid savannas in Niger and Mali. Wet deposition contributed with 37–53% of the total N flux, suggesting that wet N deposition is equally important to dry deposition fluxes for direct N loading to savanna ecosystems in the Sahel, with a large contribution of reduced compounds. This study shows that Dahra presents a precipitation chemistry composition with characteristics close to those from other Sahelian sites, with however the specificity of being more influenced by the proximity of the Atlantic ocean and the presence of livestock year round.
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| 5. |
- Martínez, Beatriz, et al.
(author)
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Evaluation of the LSA-SAF Gross Primary Production product derived from SEVIRI/MSG data (MGPP)
- 2020
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In: ISPRS Journal of Photogrammetry and Remote Sensing. - : Elsevier BV. - 0924-2716. ; 159, s. 220-236
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Journal article (peer-reviewed)abstract
- The objective of this study is to describe a completely new 10-day gross primary production (GPP) product(MGPP LSA-411) based on data from the geostationary SEVIRI/MSG satellite within the LSA SAF (Land SurfaceAnalysis SAF) as part of the SAF (Satellite Application Facility) network of EUMETSAT.The methodology relies on the Monteith approach. It considers that GPP is proportional to the absorbedphotosynthetically active radiation APAR and the proportionality factor is known as the light use efficiency ε. Aparameterization of this factor is proposed as the product of a εmax, corresponding to the canopy functioningunder optimal conditions, and a coefficient quantifying the reduction of photosynthesis as a consequence ofwater stress. A three years data record (2015–2017) was used in an assessment against site-level eddy covariance(EC) tower GPP estimates and against other Earth Observation (EO) based GPP products. The site-level comparisonindicated that the MGPP product performed better than the other EO based GPP products with 48% ofthe observations being below the optimal accuracy (absolute error < 1.0 g m−2 day−1) and 75% of these databeing below the user requirement threshold (absolute error < 3.0 g m−2 day−1). The largest discrepanciesbetween the MGPP product and the other GPP products were found for forests whereas small differences wereobserved for the other land cover types. The integration of this GPP product with the ensemble of LSA-SAF MSG
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| 6. |
- Söderholm, Johan D, 1958-, et al.
(author)
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Augmented increase in tight junction permeability by luminal stimuli in the non-inflamed ileum of crohn's disease
- 2002
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In: Gut. - : BMJ. - 0017-5749 .- 1468-3288. ; 50:3, s. 307-313
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Journal article (peer-reviewed)abstract
- Background: Crohn's disease is associated with deranged intestinal permeability in vivo, suggesting dysfunction of tight junctions. The luminal contents are important for development of neoinflammation following resection. Regulation of tight junctions by luminal factors has not previously been studied in Crohn's disease. Aims: The aim of the study was to investigate the effects of a luminal stimulus, known to affect tight junctions, on the distal ileum in patients with Crohn's disease. Patients: Surgical specimens from the distal ileum of patients with Crohn's disease (n=l 2) were studied, and ileal specimens from colon cancer patients (n=l 3) served as controls. Methods: Mucosal permeability to 51Cr-EDTA and electrical resistance were studied in Ussing chambers during luminal exposure to sodium caprate (a constituent of milk fat, affecting tight junctions) or to buffer only. The mechanisms involved were studied by mucosal ATP levels, and by electron and confocal microscopy. Results: Baseline permeability was the same in non-inflamed ileum of Crohn's disease and controls. Sodium caprate induced a rapid increase in paracellular permeability - that is, increased permeation of 51Cr-EDTA and decreased electrical resistance - which was more pronounced in non-inflamed ileum of Crohn's disease, and electron microscopy showed dilatations within the tight junctions. Moreover, sodium caprate induced disassembly of perijunctional filamentous actin was more pronounced in Crohn's disease mucosa. Mucosal permeability changes were accompanied by mitochondrial swelling and a fall in epithelial ATP content, suggesting uncoupling of oxidative phosphorylation. Conclusions: The tight junctions in the non-inflamed distal ileum of Crohn's disease were more reactive to luminal stimuli, possibly mediated via disturbed cytoskeletal contractility. This could contribute to the development of mucosal neoinflammation in Crohn's disease.
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| 7. |
- Tagesson, T., et al.
(author)
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Deriving seasonal dynamics in ecosystem properties of semi-arid savanna grasslands from in situ-based hyperspectral reflectance
- 2015
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In: Biogeosciences. - : Copernicus GmbH. - 1726-4189. ; 12:15, s. 4621-4635
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Journal article (peer-reviewed)abstract
- This paper investigates how hyperspectral reflectance (between 350 and 1800 nm) can be used to infer ecosystem properties for a semi-arid savanna grassland in West Africa using a unique in situ-based multi-angular data set of hemispherical conical reflectance factor (HCRF) measurements. Relationships between seasonal dynamics in hyperspectral HCRF and ecosystem properties (biomass, gross primary productivity (GPP), light use efficiency (LUE), and fraction of photosynthetically active radiation absorbed by vegetation (FAPAR)) were analysed. HCRF data (rho) were used to study the relationship between normalised difference spectral indices (NDSIs) and the measured ecosystem properties. Finally, the effects of variable sun sensor viewing geometry on different NDSI wavelength combinations were analysed. The wavelengths with the strongest correlation to seasonal dynamics in ecosystem properties were shortwave infrared (biomass), the peak absorption band for chlorophyll a and b (at 682 nm) (GPP), the oxygen A band at 761 nm used for estimating chlorophyll fluorescence (GPP and LUE), and blue wavelengths (rho(412)) (FAPAR). The NDSI with the strongest correlation to (i) biomass combined rededge HCRF (rho(705)) with green HCRF (rho(587)), (ii) GPP combined wavelengths at the peak of green reflection (rho(518), rho(556)), (iii) LUE combined red (rho(688)) with blue HCRF (rho(436)), and (iv) FAPAR combined blue (rho(399)) and near-infrared (rho(1295)) wavelengths. NDSIs combining near infrared and shortwave infrared were strongly affected by solar zenith an-gles and sensor viewing geometry, as were many combinations of visible wavelengths. This study provides analyses based upon novel multi-angular hyperspectral data for validation of Earth-observation-based properties of semi-arid ecosystems, as well as insights for designing spectral characteristics of future sensors for ecosystem monitoring.
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| 8. |
- Tagesson, T., et al.
(author)
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Disaggregation of SMOS soil moisture over West Africa using the Temperature and Vegetation Dryness Index based on SEVIRI land surface parameters
- 2018
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In: Remote Sensing of Environment. - : Elsevier BV. - 0034-4257. ; 206, s. 424-441
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Journal article (peer-reviewed)abstract
- The overarching objective of this study was to produce a disaggregated SMOS Soil Moisture (SM) product using land surface parameters from a geostationary satellite in a region covering a diverse range of ecosystem types. SEVIRI data at 15 min temporal resolution were used to derive the Temperature and Vegetation Dryness Index (TVDI) that served as SM proxy within the disaggregation process. West Africa (3°N 26°W; 28°N 26°E) was selected as a case study as it presents both an important North-South climate gradient and a diverse range of ecosystem types. The main challenge was to set up a methodology applicable over a large area that overcomes the constraints of SMOS (low spatial resolution) and TVDI (requires similar atmospheric forcing and triangular shape formed when plotting morning rise temperature versus fraction of vegetation cover) in order to produce a 0.05° resolution disaggregated SMOS SM product at the sub-continental scale. Consistent cloud cover appeared as one of the main constraints for deriving TVDI, especially during the rainy season and in the southern parts of the region and a large adjustment window (105 × 105 SEVIRI pixels) was therefore deemed necessary. Both the original and the disaggregated SMOS SM products described well the seasonal dynamics observed at six locations of in situ observations. However, there was an overestimation in both products for sites in the humid southern regions; most likely caused by the presence of forest. Both TVDI and the associated disaggregated SM product were found to be highly sensitive to algorithm input parameters; especially for conditions of high fraction of vegetation cover. Additionally, seasonal dynamics in TVDI did not follow the seasonal patterns of SM. Still, its spatial heterogeneity was found to be a good proxy for disaggregating SMOS SM data; main river networks and spatial patterns of SM extremes (i.e. droughts and floods) not seen in the original SMOS SM product were revealed in the disaggregated SM product for a test case of July–September 2012. The disaggregation methodology thereby successfully increased the spatial resolution of SMOS SM, with potential application for local drought/flood monitoring of importance for the livelihood of the population of West Africa.
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| 9. |
- Uman, Timur, 1981-, et al.
(author)
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Exploring the antecedents of the mental health of business professionals in Sweden
- 2020
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In: Work. - : IOS Press. - 1051-9815 .- 1875-9270. ; 67:3, s. 665-669
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Journal article (peer-reviewed)abstract
- BACKGROUND: Business professionals are an important occupational group that carries responsibility for the economic welfare of organizations and of society at large. These professionals have recently been reported to be experiencing increased mental strain, which may have a significant effect on the role they play in organizations and in society. Understanding the causes of this strain is thus an important endeavour.OBJECTIVE: This study explores the antecedents of the mental health of business professionals.METHODS: Multiple linear regression analyses were used to examine the relationship between business professionals' mental health and its demographic, work-related, and other triggers. T-tests and descriptive statistics were used to explore the gender of the respondents in relation to these triggers and mental health.RESULTS: Compared with their male counterparts, female business professionals report poorer mental health; however, no gender differences were found in job satisfaction or life satisfaction. According to this study, age, overtime pay, higher salary and position as a manager have a positive relation with mental health, whereas working overtime has a negative relation with mental health. Job satisfaction and life satisfaction are important determinants of the mental health of business professionals.CONCLUSIONS: Business professionals are important to the economic welfare of their organization and of society as a whole. Our study suggests that demographic characteristics, work-related aspects and subjective dimensions of well-being have a profound effect on the mental health of business professionals.
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