Remote sensing water observation for supporting Lake Victoria weed management

Cavalli, Rosa Maria; Laneve, Giovanni; Fusilli, Lorenzo; Pignatti, Stefano; Santini, Federico

doi:10.1016/j.jenvman.2007.07.036

Cited by 61 publications

(32 citation statements)

References 27 publications

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“…Thomson, 2007), was extracted from the mosaic. The spectra of water are modified by suspended solids, coloured dissolved organic matter and water plants, primarily shifting the peak of the reflectance from shorter wavelengths towards the red light (Cavalli et al, 2009). This spectral characteristic is used to define water bodies by means of the Normalized Difference Vegetation Index (NDVI) (Frazier and Page, 2000;Gond et al, 2004).…”

Section: Data Setsmentioning

confidence: 99%

Meteorological characteristics and potential causes of the 2007 flood in sub‐Saharan Africa

Paeth

Fink

Pohle

et al. 2011

Intl Journal of Climatology

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ABSTRACT:In August and September 2007 media and aid organizations reported on a severe flood in large parts of sub-Saharan Africa caused by a sequence of extreme rain events. However, the reporting was partly controversial and much was speculated about how unusual the flood event was. Here, we analyse various observational data sets in order to assess and to compare the spatio-temporal characteristics and intensity of the flood and the associated rain events. The return times are estimated from daily precipitation time series at fine spatial resolution, and the potential causes are disclosed in a global and regional context.Satellite data reveal that the flood was not large scale but confined to the main river basins in sub-Saharan West Africa. Nonetheless, abundant rainfall prevailed over large parts of Western Africa extending north into the Western Sahara, particularly during the second half of August and the beginning of September 2007. In detail, various precipitation data sets differ considerably in terms of the monthly anomalies, demonstrating the difficulty to delineate meteorological extreme events even at a sub-continental scale and during the most recent past. Return times typically range between 1 and 50 years with high spatial heterogeneity but amount to 1200 years in the regional mean over the Upper Volta Basin. Among the potential causes we identify a La Niña event in the tropical Pacific, anomalous heating in the tropical Atlantic coming along with a greater depth of the monsoonal westerlies, and enhanced activity of African easterly waves, both evident in 2-6 day zonal wind and outgoing longwave radiation variance anomalies.

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Section: Data Setsmentioning

confidence: 99%

Meteorological characteristics and potential causes of the 2007 flood in sub‐Saharan Africa

Paeth

Fink

Pohle

et al. 2011

Intl Journal of Climatology

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“…The post flooding image from 30 October shows much higher NDVIs in that region, so possibly the vegetation profited from high soil water contents after the surface water disappeared. The main problems identifying flooded areas especially during times of heavy rains and long standing water are suspended solid, dissolved organic matter and water plants, primarily shifting the peak of the reflectance from shorter wavelengths towards the red light (Cavalli et al, 2008). But the overall spectral characteristic remains constant and so it is still possible to determine water bodies through careful selection of thresholds (Paeth et al, 2011).…”

Section: Flooding Situationmentioning

confidence: 99%

The 2007 flood in the Sahel: causes, characteristics and its presentation in the media and FEWS NET

Samimi

Fink

Paeth

2012

Nat. Hazards Earth Syst. Sci.

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<p><strong>Abstract.</strong> During the rainy season in 2007, reports about exceptional rains and floodings in the Sahel were published in the media, especially in August and September. Institutions and organizations like the World Food Programme (WFP) and FEWS NET put the events on the agenda and released alerts and requested help. The partly controversial picture was that most of the Sahel faced a crisis caused by widespread floodings. Our study shows that the rainy season in 2007 was exceptional with regard to rainfall amount and return periods. In many areas the event had a return period between 1 and 50 yr with high spatial heterogeneity, with the exception of the Upper Volta basin, which yielded return periods of up to 1200 yr. Despite the strong rainfall, the interpretation of satellite images show that the floods were mainly confined to lakes and river beds. However, the study also proves the difficulties in assessing the meteorological processes and the demarcation of flooded areas in satellite images without ground truthing. These facts and the somewhat vague and controversial reports in the media and FEWS NET demonstrate that it is crucial to thoroughly analyze such events at a regional and local scale involving the local population.</p>

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“…The authors of [1] used an unsupervised clustering technique with thresholds based on a "wetness index", to identify water hyacinth and water hyacinth-free areas in Lake Victoria. The authors of [10] applied Minimum Distance-a simple parametric classification algorithm to identify floating vegetation areas, before applying a spectral linear mixture model-a sub-pixel analysis to discriminate different vegetation species according to the weed spectral behaviour. The most widely used method, however, is the mathematical combination of visible and near-infrared reflectance bands in the form of spectral vegetation indices [11].…”

Section: Introductionmentioning

confidence: 99%

Evaluating MERIS-Based Aquatic Vegetation Mapping in Lake Victoria

et al. 2014

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Delineation of aquatic plants and estimation of its surface extent are crucial to the efficient control of its proliferation, and this information can be derived accurately with fine resolution remote sensing products. However, small swath and low observation frequency associated with them may be prohibitive for application to large water bodies with rapid proliferation and dynamic floating aquatic plants. The information can be derived from products with large swath and high observation frequency, but with coarse resolution; and the quality of so derived information must be eventually assessed using finer resolution data. In this study, we evaluate two methods: Normalized Difference Vegetation Index (NDVI) slicing and maximum likelihood in terms of delineation; and two methods: Gutman and Ignatov's NDVI-based fractional cover retrieval and linear spectral unmixing in terms of area estimation of aquatic plants from 300 m Medium Resolution Imaging Spectrometer (MERIS) data, using as reference results obtained with 30 m Landsat-7 ETM+. Our results show for delineation, that maximum likelihood with an average classification accuracy of 80% is better than NDVI slicing at 75%, both methods showing larger errors over sparse vegetation. In area estimation, we found that Gutman and Ignatov's method and spectral unmixing produce almost the same root mean square (RMS) error of about 0.10, but the former shows larger errors of about 0.15 over sparse vegetation while the latter remains invariant. Where an endmember spectral library is available, we OPEN ACCESS Remote Sens. 2014, 6 7763 recommend the spectral unmixing approach to estimate extent of vegetation with coarse resolution data, as its performance is relatively invariant to the fragmentation of aquatic vegetation cover.

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Remote sensing water observation for supporting Lake Victoria weed management

Cited by 61 publications

References 27 publications

Meteorological characteristics and potential causes of the 2007 flood in sub‐Saharan Africa

Meteorological characteristics and potential causes of the 2007 flood in sub‐Saharan Africa

The 2007 flood in the Sahel: causes, characteristics and its presentation in the media and FEWS NET

Evaluating MERIS-Based Aquatic Vegetation Mapping in Lake Victoria

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