scholarly journals Increased Flooded Area and Exposure in the White Volta River Basin in Western Africa, Identified From Multi-source Remote Sensing Data

2021 ◽  
Author(s):  
Chengxiu Li ◽  
Jadunandan Dash ◽  
Moses Asamoah ◽  
Justin Sheffield ◽  
Mawuli Dzodzomenyo ◽  
...  
Keyword(s):  
Remote Sensing Data ◽  
Sub Saharan Africa ◽  
Flood Mapping ◽  
Spatiotemporal Pattern ◽  
Population Exposure ◽  
Accurate Information ◽  
Participatory Mapping ◽  
Western Africa ◽  
Flood Exposure ◽  
Moderate Resolution Imaging Spectroradiometer

Abstract Accurate information on flood extent and exposure is critical for disaster management in data-scarce, vulnerable regions, such as Sub-Saharan Africa (SSA). However, uncertainties in flood extent affect flood exposure estimates. This study developed a framework to examine the spatiotemporal pattern of floods and to assess flood exposure through utilization of satellite images, ground-based participatory mapping of flood extent, and socio-economic data. Drawing on a case study in the White Volta basin in Western Africa, our results showed that synergetic use of multi-temporal radar and optical satellite data improved flood mapping accuracy (77% overall agreement with participatory mapping outputs), in comparison with existing global flood datasets (43% overall agreement for the moderate-resolution imaging spectroradiometer (MODIS) Near Real-Time (NRT) Global Flood Product). Increases in flood extent were observed according to our classified product, as well as two existing global flood products. Flood exposure estimates remain highly uncertain and sensitive to the input dataset used, with the greatest farmland and infrastructure exposure estimated using a composite flood map derived from three products, with lower exposure estimated from each flood product individually. While population exposure varied greatly depending on the population dataset used. The study shows that there is considerable scope to develop an accurate flood mapping system in SSA and thereby improve flood exposure assessment and develop mitigation and intervention plans.

scholarly journals Multispectral Remote Sensing of Wetlands in Semi-Arid and Arid Areas: A Review on Applications, Challenges and Possible Future Research Directions

2020 ◽  
Vol 12 (24) ◽  
pp. 4190
Author(s):  
Siyamthanda Gxokwe ◽  
Timothy Dube ◽  
Dominic Mazvimavi
Keyword(s):  
Remote Sensing ◽  
Arid Regions ◽  
Remote Sensing Data ◽  
Sub Saharan Africa ◽  
Future Research ◽  
Multispectral Imagery ◽  
Aquatic Life ◽  
Sensing Data ◽  
Spatial Coverage ◽  
Semi Arid

Wetlands are ranked as very diverse ecosystems, covering about 4–6% of the global land surface. They occupy the transition zones between aquatic and terrestrial environments, and share characteristics of both zones. Wetlands play critical roles in the hydrological cycle, sustaining livelihoods and aquatic life, and biodiversity. Poor management of wetlands results in the loss of critical ecosystems goods and services. Globally, wetlands are degrading at a fast rate due to global environmental change and anthropogenic activities. This requires holistic monitoring, assessment, and management of wetlands to prevent further degradation and losses. Remote-sensing data offer an opportunity to assess changes in the status of wetlands including their spatial coverage. So far, a number of studies have been conducted using remotely sensed data to assess and monitor wetland status in semi-arid and arid regions. A literature search shows a significant increase in the number of papers published during the 2000–2020 period, with most of these studies being in semi-arid regions in Australia and China, and few in the sub-Saharan Africa. This paper reviews progress made in the use of remote sensing in detecting and monitoring of the semi-arid and arid wetlands, and focuses particularly on new insights in detection and monitoring of wetlands using freely available multispectral sensors. The paper firstly describes important characteristics of wetlands in semi-arid and arid regions that require monitoring in order to improve their management. Secondly, the use of freely available multispectral imagery for compiling wetland inventories is reviewed. Thirdly, the challenges of using freely available multispectral imagery in mapping and monitoring wetlands dynamics like inundation, vegetation cover and extent, are examined. Lastly, algorithms for image classification as well as challenges associated with their uses and possible future research are summarised. However, there are concerns regarding whether the spatial and temporal resolutions of some of the remote-sensing data enable accurate monitoring of wetlands of varying sizes. Furthermore, it was noted that there were challenges associated with the both spatial and spectral resolutions of data used when mapping and monitoring wetlands. However, advancements in remote-sensing and data analytics provides new opportunities for further research on wetland monitoring and assessment across various scales.

scholarly journals Impact of Monsoon-Transported Anthropogenic Aerosols and Sun-Glint on the Satellite-Derived Spectral Remote Sensing Reflectance in the Indian Ocean

2021 ◽  
Vol 13 (2) ◽  
pp. 184
Author(s):  
Rongjie Liu ◽  
Jie Zhang ◽  
Tingwei Cui ◽  
Haocheng Yu
Keyword(s):  
Remote Sensing ◽  
Indian Ocean ◽  
Infrared Imaging ◽  
Atmospheric Correction ◽  
Spatiotemporal Pattern ◽  
Anthropogenic Aerosols ◽  
Remote Sensing Reflectance ◽  
The Indian Ocean ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Terra Modis

Spectral remote sensing reflectance (Rrs(λ), sr−1) is one of the most important products of ocean color satellite missions, where accuracy is essential for retrieval of in-water, bio-optical, and biogeochemical properties. For the Indian Ocean (IO), where Rrs(λ) accuracy has not been well documented, the quality of Rrs(λ) products from Moderate Resolution Imaging Spectroradiometer onboard both Terra (MODIS-Terra) and Aqua (MODIS-Aqua), and Visible Infrared Imaging Radiometer Suite onboard the Suomi National Polar-Orbiting Partnership spacecraft (VIIRS-NPP), is evaluated and inter-compared based on a quality assurance (QA) system, which can objectively grade each individual Rrs(λ) spectrum, with 1 for a perfect spectrum and 0 for an unusable spectrum. Taking the whole year of 2016 as an example, spatiotemporal pattern of Rrs(λ) quality in the Indian Ocean is characterized for the first time, and the underlying factors are elucidated. Specifically, QA analysis of the monthly Rrs(λ) over the IO indicates good quality with the average scores of 0.93 ± 0.02, 0.92 ± 0.02 and 0.92 ± 0.02 for VIIRS-NPP, MODIS-Aqua, and MODIS-Terra, respectively. Low-quality (~0.7) data are mainly found in the Bengal Bay (BB) from January to March, which can be attributed to the imperfect atmospheric correction due to anthropogenic absorptive aerosols transported by the northeasterly winter monsoon. Moreover, low-quality (~0.74) data are also found in the clear oligotrophic gyre zone (OZ) of the south IO in the second half of the year, possibly due to residual sun-glint contributions. These findings highlight the effects of monsoon-transported anthropogenic aerosols, and imperfect sun-glint removal on the Rrs(λ) quality. Further studies are advocated to improve the sun-glint correction in the oligotrophic gyre zone and aerosol correction in the complex ocean–atmosphere environment.

scholarly journals Volumetric Quantification of Flash Flood Using Microwave Data on a Watershed Scale in Arid Environments, Saudi Arabia

2021 ◽  
Vol 13 (8) ◽  
pp. 4115
Author(s):  
Jaka Budiman ◽  
Jarbou Bahrawi ◽  
Asep Hidayatulloh ◽  
Mansour Almazroui ◽  
Mohamed Elhag
Keyword(s):  
Saudi Arabia ◽  
Flash Flood ◽  
Remote Sensing Data ◽  
Surface Elevation ◽  
Flood Mapping ◽  
Depth Information ◽  
Arid Environments ◽  
Volume Calculation ◽  
Flood Depth ◽  
Flood Volume

Actual flood mapping and quantification in an area provide valuable information for the stakeholder to prevent future losses. This study presents the actual flash flood quantification in Al-Lith Watershed, Saudi Arabia. The study is divided into two steps: first is actual flood mapping using remote sensing data, and the second is the flood volume calculation. Two Sentinel-1 images are processed to map the actual flood, i.e., image from 25 May 2018 (dry condition), and 24 November 2018 (peak flood condition). SNAP software is used for the flood mapping step. During SNAP processing, selecting the backscatter data representing the actual flood in an arid region is challenging. The dB range value from 7.23–14.22 is believed to represent the flood. In GIS software, the flood map result is converted into polygon to define the flood boundary. The flood boundary that is overlaid with Digital Elevation Map (DEM) is filled with the same elevation value. The Focal Statistics neighborhood method with three iterations is used to generate the flood surface elevation inside the flood boundary. The raster contains depth information is derived by subtraction of the flood surface elevation with DEM. Several steps are carried out to minimize the overcalculation outside the flood boundary. The flood volume can be derived by the multiplication of flood depth points with each cell size area. The flash flood volume in Al-Lith Watershed on 24 November 2018 is 155,507,439 m3. Validity checks are performed by comparing it with other studies, and the result shows that the number is reliable.

Slaves and society in Western Africa, c. 1445—c. 1700

1980 ◽  
Vol 21 (3) ◽  
pp. 289-310 ◽  
Author(s):  
J. D. Fage
Keyword(s):  
Social Mobility ◽  
Social Groups ◽  
Early Years ◽  
Sub Saharan Africa ◽  
Western Africa ◽  
The Social ◽  
African Slaves ◽  
Limited Supply ◽  
Sub Saharan

Published European first-hand accounts of the coastlands from Senegal to Angola for the period c. 1445-c. 1700 are examined to see what light they throw on the extent to which institutions of servitude in pre-colonial sub-Saharan Africa were autonomous developments or a response to external demands for African slaves. It seems clear that when, in the early years of this period, European traders first approached societies along the western African coasts, they were commonly offered what they called ‘slaves’ in exchange for the goods they had brought. But it would be wrong to conclude from this that a slave class was necessarily a feature of western African coastal societies when these were first contacted by Europeans. It is clear, for instance, that the Europeans preferred to deal with societies which had developed monarchical governments, whose leaders had control of sufficient surpluses to make trade worthwhile. The evidence suggests that in these societies most individuals were dependants of a ruling and entrepreneurial elite, but that there was also social mobility. A category of dependants that particularly attracted the notice of the European observers was women, whom men of power and wealth tended to accumulate as wives (and hence as the potential mothers of still more dependants). The necessarily limited supply of women may have been a factor encouraging such men to seek to increase their followings, and thus their status, power and wealth, by recruiting other dependants by forcible, judicial and economic means. While many such dependants, or their offspring, would be assimilated into the social groups commanded by their masters, the latter were certainly willing to contemplate using recently acquired or refractory recruits in other ways, such as exchanging them for alternative forms of wealth.

scholarly journals Global maps of aerosol single scattering albedo using combined CERES-MODIS retrieval

2021 ◽  
Author(s):  
Archana Devi ◽  
Sreedharan Krishnakumari Satheesh
Keyword(s):  
Climate Models ◽  
Radiant Energy ◽  
Energy System ◽  
Single Scattering ◽  
Global Scale ◽  
Single Scattering Albedo ◽  
Accurate Information ◽  
Climatic Impact ◽  
Aerosol Absorption ◽  
Moderate Resolution Imaging Spectroradiometer

Abstract. Single Scattering Albedo (SSA) is a leading contributor to the uncertainty in aerosol radiative impact assessments. Therefore accurate information on aerosol absorption is required on a global scale. In this study, we have applied a multi-satellite algorithm to retrieve SSA using the concept of ‘critical optical depth.’ Global maps of SSA were generated following this approach using spatially and temporally collocated data from Clouds and the Earth’s Radiant Energy System (CERES) and Moderate Resolution Imaging Spectroradiometer (MODIS) sensors on board Terra and Aqua satellites. The method has been validated using the data from aircraft-based measurements of various field campaigns. The retrieval uncertainty is ±0.03 and depends on both the surface albedo and aerosol absorption. Global mean SSA estimated over land and ocean is 0.93 and 0.97, respectively. Seasonal and spatial distribution of SSA over various regions are also presented. The global maps of SSA, thus derived with improved accuracy, provide important input to climate models for assessing the climatic impact of aerosols on regional and global scales.

scholarly journals REMOTE SENSING AND GIS FOR LAND COVER CLASSIFICATION AND CHANGE DETECTION IN GAZIPUR SADAR, BANGLADESH DURING 1973-2017

2018 ◽  
Vol 5 (2) ◽  
pp. 215
Author(s):  
Md Arafat Hassan ◽  
Rakibul Islam ◽  
Rehnuma Mahjabin
Keyword(s):  
Remote Sensing ◽  
Supervised Classification ◽  
Agricultural Land ◽  
Satellite Image ◽  
Remote Sensing Data ◽  
Remote Sensing And Gis ◽  
Vegetation Coverage ◽  
Accurate Information ◽  
Sal Forest ◽  
Shed Light

This paper has been developed to capture the land coverage change in Gazipur Sadar Upazila with the help of remote sensing data of 44 years from 1973 to 2017. After acquiring the study area image of 1973, 1991, 2006 and 2017 supervised classification method has been used to get the accurate information from the satellite image and the whole outcome has been transformed into measurable unit (sq km) and graphs. The accuracy of land coverage was ranged from 85% to 89%. The outcome says that the acceleration of economic growth and pressure of huge population took a heavy toll on the vegetation coverage which decreased -199.7%. People are destroying vegetation coverage for building up settlements and infrastructure. In the year 2017, the map shows that the built-up area increased 312.9% for industry, settlement and agricultural purpose. Moreover agricultural land also drops down from 42% to 32%.  The rapid rate of decreasing vegetation coverage and small amount of existing vegetation coverage only 57 sq km (in 2017) is a red alert for the region. The Sal forest and other special flora species of that region is valuable resource for environment. This paper shed light on the fact that it is urgent to protect vegetation coverage so it will help the authority to make good policies and use other techniques to save vegetation coverage.

scholarly journals Study of the genetic heterogeneity of SAT-2 foot-and-mouth disease virus in sub-Saharan Africa with specific focus on East Africa

2007 ◽  
Vol 74 (4) ◽  
Author(s):  
M. Sahle ◽  
R.M. Dwarka ◽  
E.H. Venter ◽  
W. Vosloo
Keyword(s):  
East Africa ◽  
Foot And Mouth Disease ◽  
Mouth Disease ◽  
Sub Saharan Africa ◽  
Gene Encoding ◽  
Western Africa ◽  
Mouth Disease Virus ◽  
Foot And Mouth ◽  
Sub Saharan ◽  
Unrelated Strain

The epidemiology of serotype SAT-2 foot-and-mouth disease was investigated in sub-Saharan Africa by phylogenetic analysis using the 1D gene encoding the major antigenic determinant. Fourteen genotypes were identified of which three are novel and belong to East Africa, bringing the total number of genotypes for that region to eight. The genotypes clustered into three lineages that demonstrated surprising links between East, southern and south-western Africa. One lineage was unique to West Africa. These results established numerous incursions across country borders in East Africa and long term conservation of sequences for periods up to 41 years. Ethiopia, Kenya and Uganda have all experienced outbreaks from more than one unrelated strain, demonstrating the potential for new introductions. The amount of variation observed within this serotype nearly equalled that which was found between serotypes; this has severe implications for disease control using vaccination.

Community geometric standards for remote sensing products

2021 ◽  
Author(s):  
Guoqing (Gary) Lin ◽  
Robert Wolfe ◽  
Bin Tan ◽  
Jaime Nickeson
Keyword(s):  
Remote Sensing ◽  
Infrared Imaging ◽  
European Space Agency ◽  
Remote Sensing Data ◽  
Performance Standards ◽  
Positional Accuracy ◽  
Factors Affecting ◽  
Remote Sensors ◽  
Data Products ◽  
Moderate Resolution Imaging Spectroradiometer

<p>We have developed a set of geometric standards for assessing earth observing data products derived from space-borne remote sensors.  We have worked with the European Space Agency (ESA) Earthnet Data Assessment Pilot (EDAP) project to provide a set of guidelines to assess geometric performance in data products from commercial electronic-optical remote sensors aboard satellites such as those from Planet Labs. The guidelines, or the standards, are based on performance from a few NASA procured sensors, such as the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors, the Visible Infrared Imaging Radiometer Suite (VIIRS) sensors and the Advanced Baseline Imager (ABI) sensors. The standards include sensor spatial response, absolute positional accuracy, and band-to-band co-registration. They are tiered in “basic”, “intermediate” and “goal” criteria. These are important geometric factors affecting scientific use of remote sensing data products. We also discuss possible approaches achieving the highest goal in geometric performance standards.</p>

scholarly journals Imported Plasmodium vivax Malaria in the Russian Federation from Western Sub-Saharan Africa

2019 ◽  
Vol 2019 ◽  
pp. 1-5 ◽  
Author(s):  
Alla Baranova ◽  
Vladimir Sergiev ◽  
Lola Morozova ◽  
Natalia Turbabina ◽  
Evgeny Morozov
Keyword(s):  
Plasmodium Vivax ◽  
Russian Federation ◽  
Sub Saharan Africa ◽  
The Past ◽  
African People ◽  
Western Africa ◽  
Plasmodium Vivax Malaria ◽  
Imported Cases ◽  
The Russian Federation ◽  
Sub Saharan

Background. Imported cases of Plasmodium vivax malaria from western Africa are reported annually in the Russian Federation. Infected native African people moving from western Africa for different purposes (students, businessmen, specialists, etc.) or Russian citizens (tourists, diplomats, businessmen, etc.) incubate the pathogen until reaching their Russian destination. Methods. All imported and other confirmed malaria cases and the associated Plasmodium species recorded over the past twenty years throughout the Russian Federation were inventoried. These data were included in the national register. The data of imported malaria cases were analysed according to the species of Plasmodium, case origin, dates of importation, and patient nationality. Results. A total of 267 P. vivax-infected patients who contracted the disease in western Africa were diagnosed in the Russian Federation from 1984 to 2017. Among them, 3 cases had mixed infections (2 with P. vivax + P. falciparum and 1 P. vivax + P. ovale). Conclusion. Our data reveal an existing risk of contracting P. vivax infections in towns of West sub-Saharan Africa despite the absence of local P. vivax infection records.

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