Exploitation of TerraSAR-X Data for Land use/Land Cover Analysis Using Object-Oriented Classification Approach in the African Sahel Area, Sudan     

Khalid Biro  Biswajeet Pradhan  Hussein Sulieman  Manfred Buchroithner 《Journal of the Indian Society of Remote Sensing》2013,41(3):539-553

Recently, object-oriented classification techniques based on image segmentation approaches are being studied using high-resolution satellite images to extract various thematic information. In this study different types of land use/land cover (LULC) types were analysed by employing object-oriented classification approach to dual TerraSAR-X images (HH and HV polarisation) at African Sahel. For that purpose, multi-resolution segmentation (MRS) of the Definiens software was used for creating the image objects. Using the feature space optimisation (FSO) tool the attributes of the TerraSAR-X image were optimised in order to obtain the best separability among classes for the LULC mapping. The backscattering coefficients (BSC) for some classes were observed to be different for HH and HV polarisations. The best separation distance of the tested spectral, shape and textural features showed different variations among the discriminated LULC classes. An overall accuracy of 84 % with a kappa value 0.82 was resulted from the classification scheme, while accuracy differences among the classes were kept minimal. Finally, the results highlighted the importance of a combine use of TerraSAR-X data and object-oriented classification approaches as a useful source of information and technique for LULC analysis in the African Sahel drylands.  相似文献   

Climate change vulnerability of sustainable forest management in the Eastern Alps   总被引：1，自引：0，他引：1  

Rupert Seidl  Werner Rammer  Manfred J. Lexer 《Climatic change》2011,106(2):225-254

Considering climatic uncertainties in management planning is a prerequisite for sustainable forest management (SFM). The aim of the study was to evaluate climate change vulnerability of the current SFM strategy for commercial forests managed by the Austrian Federal Forests. To that end vulnerability indicators were defined in a stakeholder process (selected indicators were productivity, timber and carbon stocks, biodiversity, disturbances, a tree species’ position in fundamental niche space, silvicultural flexibility and cost intensity) and their performance under climate change scenarios assessed with an ecosystem model. Multi criteria analysis techniques were employed in a partial aggregation of indicators to locate forest stands on a vulnerability surface. Results revealed high vulnerability particularly in the second half of the twenty-first century, where 39.6% of the 164.550 ha study area were assessed highly vulnerable to climate change, indicating a strong decline in the functions and services represented by the indicator system. Water-limited sites on calcareous bedrock were most negatively affected whereas assessment units at higher altitudes responded predominately positive to climate warming. The presented approach, transparently integrating multiple management objectives and allowing a quantitative comparison of vulnerabilities between sites and management strategies, contributes to the development of operational and efficient climate change adaptation measures in forest management.  相似文献   

Using panel data to estimate the effect of rainfall shocks on smallholders food security and vulnerability in rural Ethiopia     

Abera Birhanu Demeke  Alwin Keil  Manfred Zeller 《Climatic change》2011,108(1-2):185-206

Ethiopia??s agriculture is predominantly rainfed and hence any irregularity in weather conditions has adverse welfare implications. Using panel data, this paper analyzes the effect of rainfall shocks on Ethiopian rural households?? food security and vulnerability over time while controlling for a range of other factors. To this end, we generate a time-variant household food security index which is developed by principal components analysis. Based on this index, households are classified into relative food security groups and their socioeconomic differences are assessed. The exploratory results show that compared to the less secured households, the more secured ones have male and literate household heads, tend to have a greater number of economically active household members, own more livestock, experience better rainfall outcome, and participate in local savings groups. Using the food security index as the dependent variable, we use a fixed effects instrumental variable regression model to identify determinants of households?? food security over time and find that rainfall variability is an important factor. Moreover, household size, participation in local savings groups, and livestock ownership positively affect food security. Results from multinomial logistic regression model complement the fixed effects instrumental variable regression results by showing that the level and variability of rainfall are important determinants of persistent food insecurity and vulnerability. The results highlight the need for efficient risk reduction and mitigation programs to improve risk exposure and coping ability of rural households. Careful promotion of investment in infrastructure to support irrigation and water resources development is one aspect worth considering.  相似文献   

Aridity changes in the Temperate-Mediterranean transition of the Andes since ad 1346 reconstructed from tree-rings     

Duncan A. Christie  Jos�� A. Boninsegna  Malcolm K. Cleaveland  Antonio Lara  Carlos Le Quesne  Mariano S. Morales  Manfred Mudelsee  David W. Stahle  Ricardo Villalba 《Climate Dynamics》2011,36(7-8):1505-1521

The Andes Cordillera acts as regional ??Water Towers?? for several countries and encompasses a wide range of ecosystems and climates. Several hydroclimatic changes have been described for portions of the Andes during recent years, including glacier retreat, negative precipitation trends, an elevation rise in the 0° isotherm, and changes in regional streamflow regimes. The Temperate-Mediterranean transition (TMT) zone of the Andes (35.5°?C39.5°S) is particularly at risk to climate change because it is a biodiversity hotspot with heavy human population pressure on water resources. In this paper we utilize a new tree-ring network of Austrocedrus chilensis to reconstruct past variations in regional moisture in the TMT of the Andes by means of the Palmer Drought Severity Index (PDSI). The reconstruction covers the past 657?years and captures interannual to decadal scales of variability in late spring?Cearly summer PDSI. These changes are related to the north?Csouth oscillations in moisture conditions between the Mediterranean and Temperate climates of the Andes as a consequence of the latitudinal position of the storm tracks forced by large-scale circulation modes. Kernel estimation of occurrence rates reveals an unprecedented increment of severe and extreme drought events during the last century in the context of the previous six centuries. Moisture conditions in our study region are linked to tropical and high-latitude ocean-atmospheric forcing, with PDSI positively related to Ni?o-3.4 SST during spring and strongly negatively correlated with the Antarctic Oscillation (AAO) during summer. Geopotential anomaly maps at 500-hPa show that extreme dry years are tightly associated with negative height anomalies in the Ross?CAmundsen Seas, in concordance with the strong negative relationship between PDSI and AAO. The twentieth century increase in extreme drought events in the TMT may not be related to ENSO but to the positive AAO trend during late-spring and summer resulting from a gradual poleward shift of the mid-latitude storm tracks. This first PDSI reconstruction for South America demonstrates the highly significant hindcast skill of A. chilensis as an aridity proxy.  相似文献   

A global context for megadroughts in monsoon Asia during the past millennium   总被引：1，自引：0，他引：1  

Ashish Sinha  Lowell Stott  Max Berkelhammer  Hai Cheng  R. Lawrence Edwards  Brendan Buckley  Mark Aldenderfer  Manfred Mudelsee 《Quaternary Science Reviews》2011,30(1-2):47-62

Proxy reconstructions of precipitation from central India, north-central China, and southern Vietnam reveal a series of monsoon droughts during the mid 14th–15th centuries that each lasted for several years to decades. These monsoon megadroughts have no analog during the instrumental period. They occurred in the context of widespread thermal and hydrologic climate anomalies marking the onset of the Little Ice Age (LIA) and appear to have played a major role in shaping significant regional societal changes at that time. New tree ring-width based reconstructions of monsoon variability suggest episodic and widespread reoccurrences of monsoon megadroughts continued throughout the LIA. Although the El-Niño Southern Oscillation (ENSO) plays an important role in monsoon variability, there is no conclusive evidence to suggest that these megadroughts were associated with anomalous sea surface temperature anomalies that were solely the result of ENSO-like variability in the tropical Pacific. Instead, the causative mechanisms of these megadroughts may reside in protracted changes in the synoptic-scale monsoon climatology of the Indian Ocean. Today, the intra-seasonal monsoon variability is dominated by ‘active’ and the ‘break’ spells – two distinct oscillatory modes of monsoon that have radically different synoptic scale circulation and precipitation patterns. We suggest that protracted locking of the monsoon into the “break-dominated” mode – a mode that favors reduced precipitation over the Indian sub-continent and SE Asia and enhanced precipitation over the equatorial Indian Ocean, may have caused these exceptional droughts. Impetus for periodic locking of the monsoon into this mode may have been provided by cooler temperatures at the extratropical latitudes in the Northern Hemisphere which forced the mean position of the Inter-Tropical Convergence Zone (ITCZ) further southward in the Indian Ocean.  相似文献   

Volatile-induced transport of HFSE, REE, Th and U in arc magmas: evidence from zirconolite-bearing vesicles in potassic lavas of Lewotolo volcano (Indonesia)     

Jan C. M. de Hoog  Manfred J. van Bergen 《Contributions to Mineralogy and Petrology》2000,139(4):485-502

Potassium-rich calc-alkaline lavas of Lewotolo volcano, situated in the East Sunda Arc, Indonesia, contain the rare mineral zirconolite (CaZrTi₂O₇). Samples in which tiny grains of this mineral (3–25 μm in size) were found span the entire range of lava compositions (47–62 wt% SiO₂). To the best of our knowledge, this is the first record of primary zirconolite in juvenile arc volcanics. The mineral forms part of a vesicle-filling assemblage consisting of a network of quenched feldspar crystals and an SiO₂ phase, probably cristobalite. High contents of Th, U and REE (up to 9.3, 4.3 and 15.6 wt% oxide respectively) and very high Fe contents (up to 13.5 wt% Fe₂O₃) distinguish these zirconolites from those of other rock types. The extraction of volatile-rich phases with changing compositions in successive stages is considered to be responsible for the zirconolite formation. We hypothesise that a fluid capable of transporting HFSE, REE, Th and U was extracted from the magma and (partly) crystallised within voids which had formed earlier upon saturation of an aqueous fluid. Assuming that zirconolite compositions largely reflect trace metal contents of the coexisting fluid phase, significant amounts of `immobile' elements must have been transported on a macroscopic scale. Our findings thus point to a late-stage transfer of HFSE, REE, Th and U between different domains in a cooling magma body. Such a volatile-induced redistribution of trace elements at shallow levels of high-K volcanic systems may be significant for conventional geochemical modelling of magma evolution and for Th–U disequilibrium studies. Received: 3 November 1999 / Accepted: 29 February 2000  相似文献   

Style and evolution of salt pillows and related structures in the northern part of the Northeast German Basin     

Dirk Kossow  Charlotte Krawczyk  Tommy McCann  Manfred Strecker  Jörg F.W. Negendank 《International Journal of Earth Sciences》2000,89(3):652-664

The northern part of the Northeast German Basin contains a large number of Late Permian (Zechstein) salt pillows, whereas diapiric structures are almost completely absent. This lack of diapirs facilitated the study of early stages of salt movement in the basin. Salt pillows and related structures were investigated in terms of distribution, geometry and time of initiation of salt flow within the regional geological context. The primary Zechstein thickness in the study area was reconstructed to gain more insight into the relationship between the geometry of the salt layer and the style of the salt-related structures. In this study, no clear spatial relationship between the salt structures and basement faults has been found and the location of the salt structures in this area appears to be highly independent of the underlying structural grain. The overburden is affected by minor faulting. We propose that buckling of the overburden due to regional compression significantly contributed to the initiation of the Late Jurassic to Early Cretaceous salt structures in the basin. Reverse faulting of the Gardelegen and Haldensleben Faults is related to inversion tectonics and exerted a compression on the basin fill. During the deformation, the Late Permian salt layer acted as an efficient detachment and led to a marked decoupling of the Mesozoic overburden from the underlying pre-Zechstein rocks.  相似文献   

OSL and 14C chronologies of a Holocene sedimentary record (Garding‐2 core) from the German North Sea coast     

Jingran Zhang  Sumiko Tsukamoto  Alf Grube  Manfred Frechen 《Boreas: An International Journal of Quaternary Research》2014,43(4):856-868

The history of sea‐level change and sediment accumulation since the last deglaciation along the German North Sea coast is still controversial because of a limitation in the quantity and quality of chronological data. In the current study, the chronology of a 16‐ka coastal sedimentary record from the Garding‐2 core, retrieved from the Eiderstedt Peninsula in Schleswig‐Holstein, northern Germany, was established using OSL and AMS ¹⁴C dating techniques. The robust chronology using 14 radiocarbon and 25 OSL dates from the Garding‐2 core is the first long‐term record that covers the Holocene as well as the last deglaciation period in one succession in the German North Sea area. It provides a new insight into understanding the Holocene transgression and coastal accumulation histories. The combined evidence from the sedimentology and chronology investigations indicates that an estuarine environment dominated in Eiderstedt Peninsula from 16 to 13 ka, followed by a depositional hiatus between 13 and 8.3 ka, attributed to erosion caused by the Holocene transgression; the onset of the Holocene transgression at the core site occurred at around 8.3 ka. The sea level continued to rise with a decelerated rate until around 3 ka. Since 3 ka, the shoreline has begun to prograde. Foreshore (tidal flat) sediments have been deposited at the drilling site with a very high sedimentation rate of about 10 m ka^?1. At around 2 ka, a sandy beach deposit accumulated in the sedimentary succession, indicating that the coastline shifted landward, which may represent a small‐scale transgression in the late Holocene. At around 1.5 ka, terrestrial clastic sediment started to accumulate, indicating a retreat of the relative sea level in this area, which may be related to local diking activities undertaken since the 11th century.  相似文献   

Dating fluvial erosion: fluvial response to climate change in the Moselle catchment (France,Germany) since the Late Saalian     

Stéphane Cordier  Manfred Frechen  Dominique Harmand 《Boreas: An International Journal of Quaternary Research》2014,43(2):450-468

This paper focuses upon the youngest terraces of the Moselle and its tributary the Meurthe (NE France and SW Germany). It includes research on several sections, in particular the key sections of Golbey‐Pré Droué and Thörnich‐Hochrech (located in the vicinity of the Vosges Massif and in the Rhenish Massif, respectively), and the use of the Optically Stimulated Luminescence (OSL) dating method. Our investigations made it possible to obtain a more robust chronostratigraphical framework and to update the previous model of fluvial response to climate change. The results demonstrate that the Moselle terrace M3 (first terrace formed after the capture of the Upper Moselle by the Palaeo‐Meurthe) has the same age from the Vosges to the Rhenish Massif. The formation of this terrace included two main periods of sedimentation attributed to the Late Saalian (MIS 6) and the Early Weichselian (MIS 5), respectively. They were separated by a major episode of fluvial erosion that may be allocated to the MIS 6–5 transition on the basis of chronological and sedimentological evidence. This erosion led to the removal of most of the MIS 6 deposits, whereas the MIS 5 deposits have been widely preserved following the subsequent (MIS 5–4) terrace incision. This evolution somewhat contrasts with that observed in the Sarre valley, the main tributary of the Moselle, and with many fluvial systems in western Europe, which show better preservation of deposits from cold periods. This atypical behaviour is explained by the relationship between the fluvial evolution and the glaciers covering the upper Moselle catchment (Vosges Massif) during the Pleistocene cold periods.  相似文献   

Climate control on the evolution of Late Pleistocene alluvial‐fan and aeolian sand‐sheet systems in NW Germany     

Janine Meinsen  Jutta Winsemann  Julia Roskosch  Christian Brandes  Manfred Frechen  Stefan Dultz  Jürgen Böttcher 《Boreas: An International Journal of Quaternary Research》2014,43(1):42-66

The Late Pleistocene was characterized by rapid climate oscillations with alternation of warm and cold periods that lasted up to several thousand years. Although much work has been carried out on the palaeoclimate reconstruction, a direct correlation of ice‐core, marine and terrestrial records is still difficult. Here we present new data from late Middle Pleniglacial to Lateglacial alluvial‐fan and aeolian sand‐sheet deposits in northwestern Germany. Records of Late Pleniglacial alluvial fans in central Europe are very rare, and OSL dating is used to determine the timing of fan aggradation. In contrast to fluvial systems that commonly show a delay between climate change and incision/aggradation, the small alluvial‐fan systems of the Senne area responded rapidly to climatic changes and therefore act as important terrestrial climate archives for this time span. The onset of alluvial‐fan deposition correlates with the climate change from warm to cold at the end of MIS 3 (29.3±3.2 ka). Strong fan progradation started at 24.4±2.8 ka and may be related to a period of higher humidity. The vertical stacking pattern of sedimentary facies and channel styles indicate a subsequrent overall decrease in water and sediment supply, with less sustained discharges and more sporadic runoffs from the catchment area, corresponding to an increasing aridity in central Europe during the Late Pleniglacial. Major phases of channel incision and fan aggradation may have been controlled by millennial‐scale Dansgaard–Oeschger cycles. The incision of channel systems is attributed to unstable climate phases at cold–warm (dry–wet) or warm–cold (wet–dry) transitions. The alluvial‐fan deposits are bounded by an erosion surface and are overlain by aeolian sand‐sheets that were periodically affected by flash‐floods. This unconformity might be correlated with the Beuningen Gravel Bed, which is an important marker horizon in deposits of the Late Pleniglacial resulting from deflation under polar desert conditions. The deposition of aeolian sand‐sheet systems (19.6±2.1 to 13.1±1.5 ka) indicates a rapid increase in aridity at the end of the Late Pleniglacial. Intercalated flash‐floods deposits and palaeosols (Finow type) point to temporarily wet conditions during the Lateglacial. The formation of an ephemeral channel network probably marks the warm‐cold transition from the Allerød to the Younger Dryas.  相似文献