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Visar resultat 1 - 5 av 12 avhandlingar som matchar ovanstående sökkriterier.

1. 1. Mapping Primary Production for the West African Sahel with Satellite Data

   Författare :Jonathan Seaquist; Institutionen för naturgeografi och ekosystemvetenskap; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Physical geography; Sahel; CENTURY; Monte Carlo; GPP; transpiration; LUE; CLAVR; PAR; compositing; MVC; geostatistics; noise; NDVI; NOAA AVHRR; geomorphology; pedology; cartography; climatology; Fysisk geografi; geomorfologi; marklära; kartografi; klimatologi;

   Sammanfattning : A light Use Efficiency (LUE) model is developed that allows the mapping of total growing season Gross Primary Production (GPP) for the West African Sahel, using the Normalized Difference Vegetation Index (NDVI) together with other data. Image quality may be poor in monthly NDVI maximum value composites as shown by an improved geostatistical noise estimation technique. LÄS MER

3. 2. Understanding West African Monsoon Variability : Insights from Paleoclimate Modelling of Past Warm Climates

   Författare :Ellen Berntell; Qiong Zhang; Alessandra Giannini; Stockholms universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; NATURVETENSKAP; NATURAL SCIENCES; NATURVETENSKAP; NATURAL SCIENCES; West African Monsoon; Monsoon Variability; Paleoclimate; Climate modelling; naturgeografi; Physical Geography;

   Sammanfattning : The Sahel, a water-vulnerable region in West Africa, relies heavily on rainfed agriculture. The region experienced pronounced droughts during the 20th Century, emphasising the socio-economic importance of understanding the drivers of the rainfall variability. LÄS MER

4. 3. Demographic History and Adaptation in African Populations

   Författare :Mário Vicente; Carina Schlebusch; Mattias Jakobsson; Lluis Quintana-Murci; Uppsala universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; African demography; human evolutionary genetics; population structure; population admixture; genetic adaptation;

   Sammanfattning : Africa is the continent where modern humans originated and yet, African demographic history remains largely unknown. Through analyzing the genetic composition of extant and extinct individuals, it is possible to reveal signals of past demographic history and adaptation. LÄS MER

5. 4. On Sahelian-Sudan rainfall and its moisture sources

   Författare :Abubakr A. M. Salih; Qiong Zhang; Michael Tjernström; Alessandra Giannini; Stockholms universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Sudan; Sahel; rainfall; land use; deforestation; moisture sources; moisture transport; Lagrangian; moisture tagging; regional model; climate modeling; atmosfärvetenskap och oceanografi; Atmospheric Sciences and Oceanography;

   Sammanfattning : The African Sahel is one of the most vulnerable regions to climate variability at different time scales. It is an arid to semi-arid region with limited water resources. The summer rainfall is one of these sources, but it exhibits pronounced interannual variability. This thesis presents several aspects of Sahelian Sudan rainfall. LÄS MER

7. 5. Spatio-Temporal Estimation for Mixture Models and Gaussian Markov Random Fields - Applications to Video Analysis and Environmental Modelling

   Författare :Johan Lindström; Matematisk statistik; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; vegetation; time series analysis; video segmentation; spatio-temporal modelling; precipitation; Markov chain Monte Carlo; Gaussian Markov random fields; expectation maximisation; change point detection; Bayesian recursive estimation; African Sahel; adaptive Gaussian mixtures;

   Sammanfattning : In this thesis computationally intensive methods are used to estimate models and to make inference for large, spatio-temporal data sets. The thesis is divided into two parts: the first two papers are concerned with video analysis, while the last three papers model and investigate environmental data from the Sahel area in northern Africa. LÄS MER