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A GA-based stacking algorithm for predicting soil organic matter from vis-NIR spectral data
摘要： It has been demonstrated that diffuse reflectance spectroscopy in the visible and near-infrared (vis–NIR) can be exploited to predict chemical and physical soil properties. Immense soil spectral libraries (SSL) are being developed, therefore more elaborate tools that capitalize on contemporary knowledge and techniques need to be established to provide accurate predictions. In this paper, we propose a novel genetic algorithm-based stacking model that makes synergetic use of multiple models developed from different pre-processed spectral sources (termed L1 models). This is a form of ensemble learning where multiple hypotheses are combined to create a more robust and more accurate ensemble hypothesis. The genetic algorithm automatically defines the configuration of the stacked model, by selecting the best cooperating subset of the initial models. Our methodology was tested on the newly developed GEO-CRADLE SSL to predict soil organic matter (SOM). Results showed that the accuracy of prediction of the proposed method ( =0.76, and ratio of performance to inter quartile range RPIQ=2.22) was better than the one attained by the best L1 model ( =0.65, RPIQ=1.93). This approach can thus be effectively utilized to enhance the predictions of soil properties in small and large soil spectral libraries alike.
关键词： model stacking,North Africa,GEO-CRADLE,vis–NIR spectroscopy,soil spectroscopy,Middle East,Balkans
更新于2025-09-10 09:29:36
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Mapping the Leaf Economic Spectrum across West African Tropical Forests Using UAV-Acquired Hyperspectral Imagery
摘要： The leaf economic spectrum (LES) describes a set of universal trade-offs between leaf mass per area (LMA), leaf nitrogen (N), leaf phosphorus (P) and leaf photosynthesis that influence patterns of primary productivity and nutrient cycling. Many questions regarding vegetation-climate feedbacks can be addressed with a better understanding of LES traits and their controls. Remote sensing offers enormous potential for generating large-scale LES trait data. Yet so far, canopy studies have been limited to imaging spectrometers onboard aircraft, which are rare, expensive to deploy and lack fine-scale resolution. In this study, we measured VNIR (visible-near infrared (400–1050 nm)) reflectance of individual sun and shade leaves in 7 one-ha tropical forest plots located along a 1200–2000 mm precipitation gradient in West Africa. We collected hyperspectral imaging data from 3 of the 7 plots, using an octocopter-based unmanned aerial vehicle (UAV), mounted with a hyperspectral mapping system (450–950 nm, 9 nm FWHM). Using partial least squares regression (PLSR), we found that the spectra of individual sun leaves demonstrated significant (p < 0.01) correlations with LMA and leaf chemical traits: r2 = 0.42 (LMA), r2 = 0.43 (N), r2 = 0.21 (P), r2 = 0.20 (leaf potassium (K)), r2 = 0.23 (leaf calcium (Ca)) and r2 = 0.14 (leaf magnesium (Mg)). Shade leaf spectra displayed stronger relationships with all leaf traits. At the airborne level, four of the six leaf traits demonstrated weak (p < 0.10) correlations with the UAV-collected spectra of 58 tree crowns: r2 = 0.25 (LMA), r2 = 0.22 (N), r2 = 0.22 (P), and r2 = 0.25 (Ca). From the airborne imaging data, we used LMA, N and P values to map the LES across the three plots, revealing precipitation and substrate as co-dominant drivers of trait distributions and relationships. Positive N-P correlations and LMA-P anticorrelations followed typical LES theory, but we found no classic trade-offs between LMA and N. Overall, this study demonstrates the application of UAVs to generating LES information and advancing the study and monitoring tropical forest functional diversity.
关键词： hyperspectral,spectroscopy,West Africa,tropical forest,UAV,Ghana,leaf traits,PLSR,leaf economic spectrum
更新于2025-09-10 09:29:36
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Show me (more than) the money! Assessing the social and psychological dimensions to energy efficient lighting in Kenya
摘要： Despite economic, social and environmental benefits, the uptake of energy-saving compact fluorescent lamp light bulbs (CFLs) in Kibera, an informal settlement in Nairobi, remains low. We conducted a randomized controlled field experiment involving 651 Kibera residents assessing whether the joint impact of monetary incentives and behavioral interventions (pre-commitment and simplified information highlighting CFL benefits) could increase CFL uptake. A monetary incentive covering the incremental cost of a CFL compared to an incandescent bulb positively impacted uptake. However, adding simplified information more than tripled the impact of the monetary incentive alone, resulting in a remarkable uptake rate of about 84%. While a post endline survey conducted two years following the administration of the randomized control trial does not find lasting effects, this paper provides evidence for additional behavioral hypotheses in developing countries, also assessing the contribution of intelligence and measured discount rates to account for potential household present bias. It is to date the only intervention of its type that explores the extent to which behavioral interventions can complement monetary incentives.
关键词： Energy efficiency,Randomized controlled field trial,Behavioral intervention,Africa
更新于2025-09-10 09:29:36
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Barriers to Large-scale Solar Power in Tanzania
摘要： The Tanzanian official power system expansion plan shows a dominant dependence on fossil fuel-fired power plants till 2040. Hence identifying and analysing the underlying barriers for the deployment of large-scale renewables are essential. This study investigates the barriers to large-scale solar power in Tanzania. Key institutional, financial, and technological barriers are identified at different levels. The study uses a qualitative methodology where primary data is collected through 30 semi-structured interviews with experts representing the main electricity sector's stakeholders from public institutions, research institutions, private investors, civil society organizations, development partners, and financial institutions. A stakeholder-based approach which emphasizes the different perceptions of the stakeholder's groups is used to identify the barriers. Institutional barriers for the diffusion of large-scale solar power technologies are found to be predominant, and they often trigger financial and technological barriers. The study consolidates the view that foreign investment and aid directed to expand electrification in Sub-Saharan Africa need to be reshaped in order to be a driving force towards sustainable energy transition in the region. The study argues for the possibility to work on the compatible interests between the pro-renewables development partners and the Tanzanian government (which considers expanding electrification as a political priority) through introducing large-scale solar power projects that help in expanding electrification while being technically and financially supported by the development partners.
关键词： Renewable energy,Qualitative research,Tanzania,Barrier analysis,Stakeholder-based approach,Sub-Saharan Africa
更新于2025-09-10 09:29:36
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AIP Conference Proceedings [Author(s) SolarPACES 2017: International Conference on Concentrating Solar Power and Chemical Energy Systems - Santiago, Chile (26–29 September 2017)] - Systems approach to concentrated solar power (CSP) technology adoption in South Africa
摘要： To meet its future energy demand, the government of South Africa set up an Integrated Resource Plan (IRP) with the primary objective of determining its long-term electricity demand, and indicating how this demand should be met, in terms of generation type and timing. The IRP in 2010 presented the favoured energy generation techniques in SA, and it allocated 17 800 MW (42%) of the total energy mix in 2030 to renewable energy technologies (RETs). To achieve this target, the Renewable Energy Independent Power Producer Procurement Programme (REI4P) was launched and wind, solar photovoltaic (PV) and concentrating solar power (CSP) have been favoured mostly in the bids rolled out thus far. South Africa has been identified as one of the world’s best destinations for CSP because of the available solar resources, and a total of 600 MW of CSP had been purchased in the REIPPPP bids. However, the IRP update of 2016 threw CSP out of the future energy plans, when it gave no share to new electricity generation from it beyond 2030. This has created growing uncertainty of the future of CSP in South Africa. There is therefore an urgent need for collective efforts to present a broad and detailed value proposition in terms of present and prospects of CSP, and how it can be developed and deployed in the country to foster a lower tariff, encourage adoption, and ensure its return to the IRP. The study presented in this paper used a system dynamics approach to analyse the unique, critical and complex factors that affect the deployment of CSP in South Africa, as identified by concerned policy-makers, CSP experts, and existing studies. The result from this study shows that improved support for research is the most effective way to open new methods and ways in which the CSP technologies can be deployed, which will foster further CSP adoption in South Africa.
关键词： Renewable Energy Technologies (RETs),Integrated Resource Plan (IRP),South Africa,System Dynamics,Concentrated Solar Power (CSP)
更新于2025-09-09 09:28:46
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Inherited retinal disorders in South Africa and the clinical impact of evolving technologies
摘要： Retinal degenerative disorders (RDDs) encompass a group of inherited diseases characterised by vision loss. The genetic and clinical complexity poses a challenge in unravelling the molecular genetic aetiology of this group of disorders. Furthermore, the population diversity in South Africa (SA) presents researchers with a particularly complicated task. Rapid advances in the development of cutting-edge technological platforms over the past two decades, however, have assisted in overcoming some of the challenges. The RDD research team has utilised these escalating technologies, which has facilitated a corresponding increase in molecular diagnoses. A biorepository has been established and comprises ~3 200 patient DNA samples archived with many forms of RDD (including retinitis pigmentosa, macular dystrophies, Stargardt disease, Leber congenital amaurosis, Usher syndrome and Bardet Biedl syndrome). A comprehensive review is presented of the SA journey spanning 25 years, into elucidating the molecular genetic basis of various forms of RDD in SA.
关键词： molecular genetics,biorepository,genetic diagnosis,Retinal degenerative disorders,South Africa
更新于2025-09-04 15:30:14
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Adjustment of Sentinel-2 Multi-Spectral Instrument (MSI) Red-Edge Band Reflectance to Nadir BRDF Adjusted Reflectance (NBAR) and Quantification of Red-Edge Band BRDF Effects
摘要： Optical wavelength satellite data have directional re?ectance effects over non-Lambertian surfaces, described by the bidirectional re?ectance distribution function (BRDF). The Sentinel-2 multi-spectral instrument (MSI) acquires data over a 20.6? ?eld of view that have been shown to have non-negligible BRDF effects in the visible, near-infrared, and short wave infrared bands. MSI red-edge BRDF effects have not been investigated. In this study, they are quanti?ed by an examination of 6.6 million (January 2016) and 10.7 million (April 2016) pairs of forward and back scatter re?ectance observations extracted over approximately 20? × 10? of southern Africa. Non-negligible MSI red-edge BRDF effects up to 0.08 (re?ectance units) across the 290 km wide MSI swath are documented. A recently published MODIS BRDF parameter c-factor approach to adjust MSI visible, near-infrared, and short wave infrared re?ectance to nadir BRDF-adjusted re?ectance (NBAR) is adapted for application to the MSI red-edge bands. The red-edge band BRDF parameters needed to implement the algorithm are provided. The parameters are derived by a linear wavelength interpolation of ?xed global MODIS red and NIR BRDF model parameters. The ef?cacy of the interpolation is investigated using POLDER red, red-edge, and NIR BRDF model parameters, and is shown to be appropriate for the c-factor NBAR generation approach. After adjustment to NBAR, red-edge MSI BRDF effects were reduced for the January data (acquired close to the solar principal where BRDF effects are maximal) and the April data (acquired close to the orthogonal plane) for all the MSI red-edge bands.
关键词： Landsat,NBAR,POLDER,bidirectional re?ectance distribution function (BRDF),Africa,Sentinel-2,red-edge,MODIS
更新于2025-09-04 15:30:14