Permanent Water Bodies Research Articles

A New Pliocene Capybara (Rodentia, Caviidae) from Northern South America (Guajira, Colombia), and its Implications for the Great American Biotic Interchange

One of the most striking components of the modern assemblage of South American mammals is the semiaquatic capybara (Caviidae, Hydrochoerinae), the biggest rodent in the world. The large hydrochoerines are recorded from the middle Miocene to the present, mainly in high latitudes of South America. Although less known, they are also recorded in low latitudes of South America, and in Central and North America. We report the first record of capybaras from the late Pliocene of Colombia, found in deposits of the Ware Formation, Guajira Peninsula in northeastern Colombia. We analyze the phylogenetic position within Caviidae, the possible environmental changes in the Guajira Peninsula, and the implications of this finding for the understanding of the Great American Biotic Interchange. The morphological and phylogenetic analyses indicate that the hydrochoerine of the Guajira Peninsula is a new species, ?Hydrochoeropsis wayuu, and this genus is most closely related to Phugatherium. According to the latest phylogenetic results, this clade is the sister group of the lineage of the recent capybaras (Neochoerus and Hydrochoerus). ?Hydrochoeropsis wayuu is the northernmost South American Pliocene hydrochoerine record and the nearest to the Panamanian bridge. The presence of this hydrochoerine, together with the fluvio-deltaic environment of the Ware Formation, suggests that during the late Pliocene, the environment that dominated the Guajira Peninsula was more humid and with permanent water bodies, in contrast with its modern desert habitats.

Humans, water, and the colonization of Australia

The Pleistocene global dispersal of modern humans required the transit of arid and semiarid regions where the distribution of potable water provided a primary constraint on dispersal pathways. Here, we provide a spatially explicit continental-scale assessment of the opportunities for Pleistocene human occupation of Australia, the driest inhabited continent on Earth. We establish the location and connectedness of persistent water in the landscape using the Australian Water Observations from Space dataset combined with the distribution of small permanent water bodies (springs, gnammas, native wells, waterholes, and rockholes). Results demonstrate a high degree of directed landscape connectivity during wet periods and a high density of permanent water points widely but unevenly distributed across the continental interior. A connected network representing the least-cost distance between water bodies and graded according to terrain cost shows that 84% of archaeological sites >30,000 y old are within 20 km of modern permanent water. We further show that multiple, well-watered routes into the semiarid and arid continental interior were available throughout the period of early human occupation. Depletion of high-ranked resources over time in these paleohydrological corridors potentially drove a wave of dispersal farther along well-watered routes to patches with higher foraging returns.

Vegetation Structure and Hydroperiod Affect Anuran Composition in a Large Neotropical Wetland

Abstract: Anuran distribution patterns can be influenced by structural and dynamic characteristics of a habitat. In floodplains—such as the South American Pantanal wetlands—cyclic changes within terrestrial and aquatic biotopes can limit the distribution and occurrence of species. To test the influence of the habitat on the anuran community structure in the Pantanal, we recorded data on species composition and abundance at 30 sampling plots, from October 2006 to May 2007. We also recorded data on seven local environmental variables: water depth, distance to the nearest permanent water body, hydroperiod, leaf litter volume, plant cover by herbaceous plants, by monospecific stands of a bromeliad, and by shrubby/arboreal woody plants. We used multivariate statistical analyses to test for data correlation. In addition, we analyzed the degrees of associations of anuran species to habitat types. Our results revealed no influence of any of the analyzed environmental variables on the anuran species richness and ...

LONG-TERM MONITORING OF WATER DYNAMICS IN THE SAHEL REGION USING THE MULTI-SAR-SYSTEM

Abstract. Fresh water is a scarce resource in the West-African Sahel region, seasonally influenced by droughts and floods. Particularly in terms of climate change, the importance of wetlands increases for flora, fauna, human population, agriculture, livestock and fishery. Hence, access to open water is a key factor. Long-term monitoring of water dynamics is of great importance, especially with regard to the spatio-temporal extend of wetlands and drylands. It can predict future trends and facilitate the development of adequate management strategies. Lake Tabalak, a Ramsar wetland of international importance, is one of the most significant ponds in Niger and a refuge for waterbirds. Nevertheless, human population growth increased the pressure on this ecosystem, which is now degrading for all uses. The main objective of the study is a long-term monitoring of the Lake Tabalak’s water dynamics to delineate permanent and seasonal water bodies, using weather- and daytime-independent multi-sensor and multi-temporal Synthetic Aperture Radar (SAR) data available for the study area. Data of the following sensors from 1993 until 2016 are used: Sentinel-1A, TerraSARX, ALOS PALSAR-1/2, Envisat ASAR, RADARSAT-1/2, and ERS-1/2. All SAR data are processed with the Multi-SAR-System, unifying the different characteristics of all above mentioned sensors in terms of geometric, radiometric and polarimetric resolution to a consistent format. The polarimetric representation in Kennaugh elements allows fusing single-polarized data acquired by older sensors with multi-polarized data acquired by current sensors. The TANH-normalization guarantees a consistent and therefore comparable description in a closed data range in terms of radiometry. The geometric aspect is solved by projecting all images to an earth-fixed coordinate system correcting the brightness by the help of the incidence angle. The elevation model used in the geocoding step is the novel global model produced by the TanDEM-X satellite mission. The advantage of the Multi-SAR-System is that it comprises ortho-rectification, radiometric enhancement, normalization and Kennaugh decomposition, independent from sensors, modes, polarizations or acquisition date of SAR data. In addition, optical satellite data can be included as well, to fill gaps where SAR data are missing due to the special normalization scheme. This kind of pre-processing is exclusively implemented at the Earth Observation Center of the German Aerospace Center in Oberpfaffenhofen, Germany. Therefore, the dynamic change of the open water of the Lake Tabalak could be classified over dry and rainy seasons and years, using different SAR data. The study provides a unique database and contributes to a better understanding of wetland systems in the Sahel region influenced by human pressure and climate change.

LONG-TERM MONITORING OF WATER DYNAMICS IN THE SAHEL REGION USING THE MULTI-SAR-SYSTEM

Fresh water is a scarce resource in the West-African Sahel region, seasonally influenced by droughts and floods. Particularly in terms of climate change, the importance of wetlands increases for flora, fauna, human population, agriculture, livestock and fishery. Hence, access to open water is a key factor. Long-term monitoring of water dynamics is of great importance, especially with regard to the spatio-temporal extend of wetlands and drylands. It can predict future trends and facilitate the development of adequate management strategies. Lake Tabalak, a Ramsar wetland of international importance, is one of the most significant ponds in Niger and a refuge for waterbirds. Nevertheless, human population growth increased the pressure on this ecosystem, which is now degrading for all uses. The main objective of the study is a long-term monitoring of the Lake Tabalak’s water dynamics to delineate permanent and seasonal water bodies, using weather- and daytime-independent multi-sensor and multi-temporal Synthetic Aperture Radar (SAR) data available for the study area. Data of the following sensors from 1993 until 2016 are used: Sentinel-1A, TerraSARX, ALOS PALSAR-1/2, Envisat ASAR, RADARSAT-1/2, and ERS-1/2. All SAR data are processed with the Multi-SAR-System, unifying the different characteristics of all above mentioned sensors in terms of geometric, radiometric and polarimetric resolution to a consistent format. The polarimetric representation in Kennaugh elements allows fusing single-polarized data acquired by older sensors with multi-polarized data acquired by current sensors. The TANH-normalization guarantees a consistent and therefore comparable description in a closed data range in terms of radiometry. The geometric aspect is solved by projecting all images to an earth-fixed coordinate system correcting the brightness by the help of the incidence angle. The elevation model used in the geocoding step is the novel global model produced by the TanDEM-X satellite mission. The advantage of the Multi-SAR-System is that it comprises ortho-rectification, radiometric enhancement, normalization and Kennaugh decomposition, independent from sensors, modes, polarizations or acquisition date of SAR data. In addition, optical satellite data can be included as well, to fill gaps where SAR data are missing due to the special normalization scheme. This kind of pre-processing is exclusively implemented at the Earth Observation Center of the German Aerospace Center in Oberpfaffenhofen, Germany. Therefore, the dynamic change of the open water of the Lake Tabalak could be classified over dry and rainy seasons and years, using different SAR data. The study provides a unique database and contributes to a better understanding of wetland systems in the Sahel region influenced by human pressure and climate change.

WETLAND MAPPING WITH SAR/QUAD-POL DATA ACQUIRED DURING TANDEM-X SCIENCE PHASE

The aim of this study was to exploit fully polarimetric SAR data acquired during TanDEM-X – Science Phase (2014/2015) over herbaceous wetlands of the Biebrza National Park (BbNP) in North-Eastern Poland for mapping seasonally flooded grasslands and permanent natural vegetation associations. The main goal of this work was to estimate the advantage of fully polarimetric radar images (QuadPol) versus alternative polarization (AltPol) modes. The methodology consisted in processing of several data subsets through polarimetric decompositions of complex quad-pol datasets, classification of multitemporal backscattering images, complementing backscattering images with Shannon Entropy, exploitation of interferometric coherence from tandem operations. In each case the multidimensional stack of images has been classified using ISODATA unsupervised clustering algorithm. With 6 QUAD-POL TSX/TDX acquisitions it was possible to distinguish correctly 5 thematic classes related to their water regime: permanent water bodies, temporarily flooded areas, wet grasslands, dry grasslands and common reed. This last category was possible to distinguish from deciduous forest only with Yamaguchi 4 component decomposition. The interferometric coherence calculated for tandem pairs turned out not so efficient as expected for this wetland mapping.

WETLAND MAPPING WITH SAR/QUAD-POL DATA ACQUIRED DURING TANDEM-X SCIENCE PHASE

Abstract. The aim of this study was to exploit fully polarimetric SAR data acquired during TanDEM-X – Science Phase (2014/2015) over herbaceous wetlands of the Biebrza National Park (BbNP) in North-Eastern Poland for mapping seasonally flooded grasslands and permanent natural vegetation associations. The main goal of this work was to estimate the advantage of fully polarimetric radar images (QuadPol) versus alternative polarization (AltPol) modes. The methodology consisted in processing of several data subsets through polarimetric decompositions of complex quad-pol datasets, classification of multitemporal backscattering images, complementing backscattering images with Shannon Entropy, exploitation of interferometric coherence from tandem operations. In each case the multidimensional stack of images has been classified using ISODATA unsupervised clustering algorithm. With 6 QUAD-POL TSX/TDX acquisitions it was possible to distinguish correctly 5 thematic classes related to their water regime: permanent water bodies, temporarily flooded areas, wet grasslands, dry grasslands and common reed. This last category was possible to distinguish from deciduous forest only with Yamaguchi 4 component decomposition. The interferometric coherence calculated for tandem pairs turned out not so efficient as expected for this wetland mapping.

Mapping Wetlands in Zambia Using Seasonal Backscatter Signatures Derived from ENVISAT ASAR Time Series

Wetlands are considered a challenging environment for mapping approaches based on Synthetic Aperture Radar (SAR) data due to their often complex internal structures and the diverse backscattering mechanisms caused by vegetation, soil moisture and flood dynamics contributing to the resulting imagery. In this study, a time series of >100 SAR images acquired by ENVISAT during a time period of ca. two years over the Kafue River basin in Zambia was compared to water heights derived from radar altimetry and surface soil moisture from a reanalysis dataset. The backscatter time series were analyzed using a harmonic model to characterize the seasonality in C-band backscatter caused by the interaction of flood and soil moisture dynamics. As a result, characteristic seasonal signatures could be derived for permanent water bodies, seasonal open water, persistently flooded vegetation and seasonally flooded vegetation. Furthermore, the analysis showed that the influence of local incidence angle could be accounted for by a linear shift in backscatter averaged over time, even in wetland areas where the dominant scattering mechanism can change depending on the season. The retrieved harmonic model parameters were then used in an unsupervised classification to detect wetland backscattering classes at the regional scale. A total area of 7800 km2 corresponding to 7.6% of the study area was classified as either one of the wetland backscattering classes. The results demonstrate the value of seasonality parameters extracted from C-band SAR time series for wetland mapping.

A retrospective study of the prevalence of bovine fasciolosis at major abattoirs in Botswana.

A retrospective study covering a period of ten years (2001–2010) was conducted using postmortem meat inspection records of the Department of Veterinary Services in Gaborone to determine the prevalence of bovine fasciolosis in Botswana. Meat inspection records of monthly and annual returns from the two main export abattoirs in the country were examined, as well as the data collected on the total number of cattle slaughtered and the number of livers condemned due to Fasciola gigantica infection. Only 1250 of the approximately 1.4 million cattle slaughtered were infected with F. gigantica (0.09%, 95% confidence intervals [CI] 0.0% – 0.3%). No distinct seasonal pattern was observed in condemnation rates of livers. However, the pattern of distribution of fasciolosis was higher (but not significant) in cattle that originated from areas with high rainfall and more permanent water bodies than those from relatively low rainfall areas with a transitory water system. It is recommended that a longitudinal survey should be carried out at the abattoirs and farms to determine the prevalence of the disease in cattle of different ages, sex and breed as well as the place of origin in the country. The present study indicated that the prevalence of fasciolosis in cattle is low and the disease is therefore of less significance in Botswana than other African countries for which information is available.

Grazing deteriorates the soil carbon stocks of Caatinga forest ecosystems in Brazil

Grazing by domestic ungulates can have substantial impacts on forests in arid and semi-arid regions, possibly including severe loss of carbon from the soil. Predicting net livestock impacts on soil organic carbon stocks remains challenging, however, due to the dependence on animal loads and on soil and environmental parameters. The objective of this study was to better understand grazing effects on soil organic carbon in seasonal tropical dry forests of north-eastern Brazil (Caatinga) by quantifying carbon stocks of the upper soil profile (0–5cm depth) and greater soil depths (>5cm depth down to bedrock) along a gradient of grazing intensity while accounting for other influencing factors such as soil texture, vegetation, landscape topography, and water availability. We analysed soil organic carbon, soil clay content, altitude above sea level, soil depth to bedrock, distance to the nearest permanent water body, species diversity of perennial plants and aboveground biomass on 45 study plots located in the vicinity of the Itaparica Reservoir, Pernambuco, Brazil. Livestock (mainly goats and cattle) are unevenly distributed in the studied ecosystem, thus grazing intensity was accounted for based on the weight of livestock droppings per square metre and classified as no or light, intermediate, or heavy grazing. The mean soil organic carbon in the area was 16.86±1.28Mgha−1C with approximately one-quarter found in the upper 5cm of the soil profile (4.14±0.43Mgha−1C) and the remainder (12.57±0.97Mgha−1C) in greater soil depths (>5cm). Heavy grazing led to significantly lower soil organic carbon stocks in the upper 5cm, whereas no effect on soil organic carbon of the soil overall or in greater soil depths was detectable. The soil’s clay content and the altitude proved to be the most relevant factors influencing overall soil organic carbon stocks and those in greater soil depths (>5cm). Our findings suggest that grazing causes substantial release of carbon from Brazilian dry forest soils, which should be addressed through improved grazing management via a legally compulsory rotation system. This would ultimately contribute to the conservation of a unique forest system and associated ecosystem services.

Epidemiology of brucellosis, Q Fever and Rift Valley Fever at the human and livestock interface in northern Côte d’Ivoire

Northern Côte d’Ivoire is the main livestock breeding zone and has the highest livestock cross-border movements in Côte d’Ivoire. The aim of this study was to provide updated epidemiological data on three neglected zoonotic diseases, namely brucellosis, Q Fever and Rift Valley Fever (RVF). We conducted three-stage cross-sectional cluster surveys in livestock and humans between 2012 and 2014 in a random selection of 63 villages and a sample of 633 cattle, 622 small ruminants and 88 people. We administered questionnaires to capture risk factors and performed serological tests including the Rose Bengal Plate Test (RBPT), Brucella spp. indirect and competitive ELISAs, Coxiella burnetii indirect ELISA and RVF competitive ELISA. The human seroprevalence for Brucella spp. was 5.3%. RBPT-positive small ruminants tested negative by the indirect ELISA. The seroprevalence of Brucella spp. in cattle adjusted for clustering was 4.6%. Cattle aged 5–8 years had higher odds of seropositivity (OR=3.5) than those aged ≤4years. The seropositivity in cattle was associated with having joint hygromas (OR=9), sharing the pastures with small ruminants (OR=5.8) and contact with pastoralist herds (OR=11.3). The seroprevalence of Q Fever was 13.9% in cattle, 9.4% in sheep and 12.4% in goats. The seroprevalence of RVF was 3.9% in cattle, 2.4% in sheep and 0% in goats. Seropositive ewes had greater odds (OR=4.7) of abortion than seronegative ones. In cattle, a shorter distance between the night pens and nearest permanent water bodies was a protective factor (OR=0.1). The study showed that the exposure to the three zoonoses is rather low in northern Côte d’Ivoire. Within a One Health approach, cost-benefit and cost-effectiveness of control measures should be assessed for an integrated control.

Sex-specific functional responses of dragonfly naiads Rhodothemis rufa on Culex quinquefasciatus larvae in laboratory bioassay

ABSTRACTLaboratory bioassay was conducted to establish the biocontrol potentiality of naiads (aquatic nymphal stage) of Rhodothemis rufa (Rambur, 1842) against larvae of Culex quinquefasciatus, a common vector of filariasis in Tropical countries. From the study, it was noticed that in laboratory condition, the rate of predation of males of R. rufa was higher than that of females of almost same size and same species. The results of the present study revealed that both sexes displayed a density-dependent decelerating type-II functional response as the logistic regression estimated a significant negative linear parameter (P1 value of −0.330 and −0.151 for males and females, respectively). Attack rate was almost similar for both sexes (0.082); however, handling time is less in males (0.62 min) than in females (0.852 min). The predator species usually coexist in the same aquatic habitat to that of mosquito larvae and can be effectively used in field condition to reduce the larval densities of mosquitoes in temporary or permanent aquatic water bodies.

多時期Landsatデータ解析を用いた全球水面マスクの高解像度化

Separation of permanent water body and temporal water body is essential for the grasp of global water distribution. Global 3-second Water Body Map (G3WBM) is a global scale high-resolution water body map recently-developed by the authors, which separates water body types by the idea of water frequency, using multi-temporal Landsat data. In this paper, we further improved the accuracy and computational efficiency of G3WBM algorithms, and refined the resolution from 90m to 30m. The validation against U.S. National Hydrography Dataset revealed that, although some small water bodies could not be visualized, more than 85% of permanent water bodies were classified correctly. Comparison between the water body mask constructed in this paper and G3WBM in the U.S. showed that water judgment accuracy was improved and over 2600km2 of temporal water has been newly separated from permanent water.

Haematococcus: a successful air-dispersed colonist in ephemeral waters is rarelyfound in phytoplankton communities

In a literature search, the presence of Haematococcus in phytoplankton communities and its biogeography were investigated. Haematococcus, although showing a wide biogeographical distribution, has been rarely found in phytoplankton communities. Simultaneously, the colonization potential of air-dispersed Haematococcus in ephemeral waters and its interactions with coexisting phytoplankton taxa were examined by microscopy and molecular methods. Haematococcus was a successful colonist, appearing among the first taxa in the experimental containers. According to principal component analysis, Haematococcus growth rate was negatively correlated with the abundance and species richness of the other autotrophs. Furthermore, a negative correlation between Haematococcus and Chlamydomonas and a positive one between Haematococcus and Chlorella were found. Overall, Haematococcus appears to be an effective air-dispersed alga that can successfully colonize and establish populations in small ephemeral water bodies. However, its absence from phytoplankton in larger permanent water bodies could be related to its high light requirements, its competitive disadvantages against other algae, and the grazing pressures from predators. The results of our study suggest a life strategy based on adaptation to higher light intensities in very shallow waters compared with optical dense lakes. Therefore, ephemeral waters are the regular habitat for Haematococcus instead of being stepping stones for the colonization of lake phytoplankton.

The importance of flooded terrestrial habitats for larval fish in a semi-natural large floodplain (Volga, Russian Federation)

We assessed the importance of flooded terrestrial habitats for fish larvae in a semi-natural large floodplain (Volga, Russian Federation) by comparing abundances at the shoreline of permanent waterbodies with flooded terrestrial habitats. We found that overall larval abundance at the shoreline of permanent waterbodies was 6 to 10 times higher than in flooded terrestrial habitats and was highly consistent over the sampled waterbodies during the 2 year study. The potential mechanisms underlying these results are that shoreline habitats receive an influx of food with retreating warmer water from flooded terrestrial habitats, whereas the risk of hypoxia and stranding is lower at the shoreline than in flooded terrestrial habitats. Furthermore, the risk of predation is also lower at the shoreline compared to the open water habitats. Thus, we hypothesize that, rather than directly providing nursery habitat, the most important function of flooded terrestrial areas for the recruitment of fish in river floodplains is the production of food organisms that become available for larvae and juveniles with the retreating water.

Development of a global ~90m water body map using multi-temporal Landsat images

Abstract This paper describes the development of a Global 3 arc-second Water Body Map (G3WBM), using an automated algorithm to process multi-temporal Landsat images from the Global Land Survey (GLS) database. We used 33,890 scenes from 4 GLS epochs in order to delineate a seamless water body map, without cloud and ice/snow gaps. Permanent water bodies were distinguished from temporal water-covered areas by calculating the frequency of water body existence from overlapping, multi-temporal, Landsat scenes. By analyzing the frequency of water body existence at 3 arc-second resolution, the G3WBM separates river channels and floodplains more clearly than previous studies. This suggests that the use of multi-temporal images is as important as analysis at a higher resolution for global water body mapping. The global totals of delineated permanent water body area and temporal water-covered area are 3.25 and 0.49 million km2 respectively, which highlights the importance of river-floodplain separation using multi-temporal images. The accuracy of the water body classification was validated in Hokkaido (Japan) and in the contiguous United States using an existing water body databases. There was almost no commission error, and about 70% of lakes > 1 km2 shows relative water area error

Strengths and weaknesses of multi-year Envisat ASAR backscatter measurements to map permanent open water bodies at global scale

Abstract The mapping of water bodies at global scale has been undertaken primarily using multi-spectral optical Earth Observation data. Limitations of optical data associated with non-uniform and temporally variable spectral signatures suggested investigating alternative approaches towards a more consistent and reliable detection of water bodies. Multi-year (2005–2012) observations of SAR backscattered intensities at moderate resolution from the Envisat Advanced Synthetic Aperture Radar (ASAR) instrument were used in this study to generate an indicator of open permanent water bodies (SAR-WBI) for the year 2010 time frame and for all land surfaces excluding Antarctica and the Greenland ice sheet. A first map of potential water bodies with a spatial resolution of 150 m was obtained with a global detection algorithm based on a set of thresholds applied to multi-temporal metrics of the SAR backscatter (temporal variability, TV, and minimum backscatter, MB). Local refinements were then used to reduce systematic commission and omission errors (4.6% of the total area mapped) due to the similarity of TV and MB over open water bodies and other land surface types primarily in cold and arid environments. The refinement rules are here explained by means of a detailed signature analysis of the SAR backscatter in such environments. The accuracy of the SAR-WBI was 80% when compared against 2078 manually interpreted footprints with a size of 150 × 150 m2. Omission errors were primarily observed along coast- and shorelines whereas commission errors were associated with (i) ephemeral water bodies, (ii) seasonally inundated areas, and (iii) an incorrect choice of the local refinement.

Factors driving the distribution of an endangered amphibian toward an industrial landscape in Australia

Although human-modified habitats often result in a loss of biodiversity, some have been found to serve as habitat refuges for threatened species. Given the globally declining status of amphibians, understanding why some species are found in heavily modified environments is of considerable interest. We used the endangered green and golden bell frog (Litoria aurea) as a model to investigate the factors influencing their distribution toward industrial areas within a landscape. The number of permanent waterbodies within a kilometer of surveyed sites was the best predictor of L. aurea occupancy, abundance and reproduction. It appears that industrial activities, such as dredging and waste disposal inadvertently created refuge habitat for L. aurea to fortuitously persist in a heavily modified landscape. Future conservation plans should mimic the positive effects of industrialization, such as increasing the number of permanent waterbodies, especially in areas containing ephemeral or isolated waterbodies and threatened with drought. Our findings also suggest that despite amphibians being relatively small animals, some species may require a larger landscape than anticipated. Recognizing life history traits, in combination with a landscape-based approach toward species with perceived limited motility, may result in more successful conservation outcomes. Identifying why threatened species persist in heavily disturbed landscapes, such as industrial sites, can provide direction toward future conservation efforts to prevent and reverse their decline.

Image Fusion-Based Change Detection for Flood Extent Extraction Using Bi-Temporal Very High-Resolution Satellite Images

Change detection based on satellite images acquired from an area at different dates is of widespread interest, according to the increasing number of flood-related disasters. The images help to generate products that support emergency response and flood management at a global scale. In this paper, a novel unsupervised change detection approach based on image fusion is introduced. The approach aims to extract the reliable flood extent from very high-resolution (VHR) bi-temporal images. The method takes an advantage of the spectral distortion that occurs during image fusion process to detect the change areas by flood. To this end, a change candidate image is extracted from the fused image generated with bi-temporal images by considering a local spectral distortion. This can be done by employing a universal image quality index (UIQI), which is a measure for local evaluation of spectral distortion. The decision threshold for the determination of changed pixels is set by applying a probability mixture model to the change candidate image based on expectation maximization (EM) algorithm. We used bi-temporal KOMPSAT-2 satellite images to detect the flooded area in the city of N′djamena in Chad. The performance of the proposed method was visually and quantitatively compared with existing change detection methods. The results showed that the proposed method achieved an overall accuracy (OA = 75.04) close to that of the support vector machine (SVM)-based supervised change detection method. Moreover, the proposed method showed a better performance in differentiating the flooded area and the permanent water body compared to the existing change detection methods.

Mapping paddy rice planting areas through time series analysis of MODIS land surface temperature and vegetation index data

Knowledge of the area and spatial distribution of paddy rice is important for assessment of food security, management of water resources, and estimation of greenhouse gas (methane) emissions. Paddy rice agriculture has expanded rapidly in northeastern China in the last decade, but there are no updated maps of paddy rice fields in the region. Existing algorithms for identifying paddy rice fields are based on the unique physical features of paddy rice during the flooding and transplanting phases and use vegetation indices that are sensitive to the dynamics of the canopy and surface water content. However, the flooding phenomena in high latitude area could also be from spring snowmelt flooding. We used land surface temperature (LST) data from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor to determine the temporal window of flooding and rice transplantation over a year to improve the existing phenology-based approach. Other land cover types (e.g., evergreen vegetation, permanent water bodies, and sparse vegetation) with potential influences on paddy rice identification were removed (masked out) due to their different temporal profiles. The accuracy assessment using high-resolution images showed that the resultant MODIS-derived paddy rice map of northeastern China in 2010 had a high accuracy (producer and user accuracies of 92% and 96%, respectively). The MODIS-based map also had a comparable accuracy to the 2010 Landsat-based National Land Cover Dataset (NLCD) of China in terms of both area and spatial pattern. This study demonstrated that our improved algorithm by using both thermal and optical MODIS data, provides a robust, simple and automated approach to identify and map paddy rice fields in temperate and cold temperate zones, the northern frontier of rice planting.