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Satellite Data (satellite + data)
Selected AbstractsAmazon Forest Structure from IKONOS Satellite Data and the Automated Characterization of Forest Canopy PropertiesBIOTROPICA, Issue 2 2008Michael Palace ABSTRACT We developed an automated tree crown analysis algorithm using 1-m panchromatic IKONOS satellite images to examine forest canopy structure in the Brazilian Amazon. The algorithm was calibrated on the landscape level with tree geometry and forest stand data at the Fazenda Cauaxi (3.75° S, 48.37° W) in the eastern Amazon, and then compared with forest stand data at Tapajos National Forest (3.08° S, 54.94° W) in the central Amazon. The average remotely sensed crown width (mean ± SE) was 12.7 ± 0.1 m (range: 2.0,34.0 m) and frequency of trees was 76.6 trees/ha at Cauaxi. At Tapajos, remotely sensed crown width was 13.1 ± 0.1 m (range: 2.0,38.0 m) and frequency of trees was 76.4 trees/ha. At both Cauaxi and Tapajos, the remotely sensed average crown widths were within 3 percent of the crown widths derived from field measurements, although crown distributions showed significant differences between field-measured and automated methods. We used the remote sensing algorithm to estimate crown dimensions and forest structural properties in 51 forest stands (1 km2) throughout the Brazilian Amazon. The estimated crown widths, tree diameters (dbh), and stem frequencies differed widely among sites, while estimated biomass was similar among most sites. Sources of observed errors included an inability to detect understory crowns and to separate adjacent, intermingled crowns. Nonetheless, our technique can serve to provide information about structural characteristics of large areas of unsurveyed forest throughout Amazonia. [source] A revised Canadian perspective: progress in glacier hydrologyHYDROLOGICAL PROCESSES, Issue 1 2005D. Scott Munro Abstract Current research into glacier hydrology is occurring at a time when glaciers around the world, particularly those whose hydrological regimes affect populated areas, are shrinking as they go through a state of perpetual negative annual mass balance. Small glaciers alone are likely to contribute 0·5 to 1 mm year,1 to global sea-level rise, with associated reductions in local freshwater resources, impacts upon freshwater ecosystems and increased risk of hazard due to outburst floods. Changes to the accumulation regimes of glaciers and ice sheets may be partly responsible, so the measurement and distribution of snowfall in glacierized basins, a topic long represented in non-glacierized basin research, is now beginning to receive more attention than it did before, aided by the advent of reliable automatic weather stations that provide data throughout the year. Satellite data continue to be an important information source for summer meltwater estimation, as distributed models, and their need for albedo maps, continue to develop. This further entails the need for simplifications to energy balance components, sacrificing point detail so that spatial calculation may proceed more quickly. The understanding of surface meltwater routing through the glacier to produce stream outflow continues to be a stimulating area of research, as demonstrated by activity at the Trapridge Glacier, Canada, and Canadian involvement in the Haut Glacier d'Arolla, Switzerland. As Canadian glacier monitoring continues to evolve, effort must be directed toward developing situations where mass balance, meltwater generation and flow routing studies can be done together at selected sites. Copyright © 2005 John Wiley & Sons, Ltd. [source] Contemporary landscape burning patterns in the far North Kimberley region of north-west Australia: human influences and environmental determinantsJOURNAL OF BIOGEOGRAPHY, Issue 8 2004T. Vigilante Abstract Aim, This study of contemporary landscape burning patterns in the North Kimberley aims to determine the relative influences of environmental factors and compare the management regimes occurring on Aboriginal lands, pastoral leases, national park and crown land. Location, The study area is defined at the largest scale by Landsat Scene 108,70 that covers a total land area of 23,134 km2 in the North Kimberley Bioregion of north-west Australia, including the settlement of Kalumburu, coastline between Vansittart Bay in the west and the mouth of the Berkeley River in the east, and stretching approximately 200 km inland. Methods, Two approaches are applied. First, a 10-year fire history (1990,1999) derived from previous study of satellite (Landsat-MSS) remote sensing imagery is analysed for broad regional patterns. And secondly, a 2-year ground-based survey of burning along major access roads leading to an Aboriginal community is used to show fine-scale burning patterns. anova and multiple regression analyses are used to determine the influence of year, season, geology, tenure, distance from road and distance from settlement on fire patterns. Results, Satellite data indicated that an average of 30.8% (±4.4% SEM) of the study area was burnt each year with considerable variability between years. Approximately 56% of the study area was burnt on three or more occasions over the 10-year period. A slightly higher proportion of burning occurred on average in the late dry season (17.2 ± 3.6%), compared with the early dry season (13.6 ± 3.3%). The highest fire frequency occurred on basalt substrates, on pastoral tenures, and at distances 5,25 km from roads. Three-way anova demonstrated that geological substrate and land use were the most significant factors influencing fire history, however a range of smaller interactions were also significant. Analysis of road transects, originating from an Aboriginal settlement, showed that the timing of fire and geology type were the most significant factors affecting the pattern of area burnt. Of the total transect area, 28.3 ± 2.9% was burnt annually with peaks in burning occurring into the dry season months of June, August and September. Basalt uplands (81.2%) and lowlands (30.1%) had greater areas burnt than sandstone (12.3%) and sands (17.7%). Main conclusions, Anthropogenic firing is constrained by two major environmental determinants; climate and substrate. Seasonal peaks in burning activity in both the early and late dry season relate to periods of optimal fire-weather conditions. Substrate factors (geology, soils and physiognomy) influence vegetation-fuel characteristics and the movement of fire in the landscape. Basalt hills overwhelmingly supported the most frequent wildfire regime in the study region because of their undulating topography and relatively fertile soils that support perennial grasslands. Within these spatial and temporal constraints people significantly influenced the frequency and extent of fire in the North Kimberley thus tenure type and associated land uses had a significant influence on fire patterning. Burning activity is high on pastoral lands and along roads and tracks on some tenure types. While the state government uses aerial control burning and legislation to try to restrict burning to the early dry season across all geology types, in practice burning is being conducted across the full duration of the dry season with early dry season burning focused on sandstone and sand substrates and late dry season burning focused on basalt substrates. There is greater seasonal and spatial variation in burning patterns on landscapes managed by Aboriginal people. [source] Assessment of impact of aquaculture on Kolleru Lake (India) using remote sensing and Geographical Information SystemAQUACULTURE RESEARCH, Issue 16 2006Marappan Jayanthi Abstract Aquaculture is one of the fastest growing food industries and the rapid growth of aquaculture worldwide has resulted in growing concerns about its impact on important ecosystems. Kolleru Lake, India's largest fresh water body, and Ramsar site have undergone tremendous changes due to the development of aquaculture. To assess the impact of aquaculture on Kolleru, satellite data were found appropriate because of the synoptic-detailed overview and accuracy. Satellite data of IRS 1D, LISS III from 2004 and Survey of India topographic maps from 1967 were processed using image processing techniques in erdas imagine and analysed in Geographical Information System (GIS) such as arc gis 9.1. Land use map prepared from the satellite data was verified in the field using Global Positioning System to check the land and water use classes and its areal extent. It was estimated from the topographic maps of 1967 that the total lake boundary area was 180.38 km2, in which 70.70 km2 had water throughout the year and 100.97 km2 had water during the rainy season. The digital image processing of 2004 satellite data revealed that Kolleru was no longer a lake and the lake area of 62.65 km2 (34.73%) only remained in a degraded state, extensively colonized by macrophytes. The total loss of lake area was 109.02 km2 between 1967 and 2004, in which aquaculture was developed in 99.74 km2, which represented 55.3% of the 1967 lake area. The maximum conversion to aquaculture occurred from the lake liable to be inundated during the 1967 rainy season. The area under agriculture was 16.62 km2 in 2004, the increase in lake area for agriculture between 1967 and 2004 being 8.22 km2 (4.55% of lake). If human induced degradation is allowed to continue, the lake will very soon disappear. Now, the Government of Andhra Pradesh, India, has initiated schemes and laws to restore the lake to its pre-development state. Lessons learnt from the Kolleru Lake cautioned that there is a need for regular monitoring of important water resources throughout the world to protect the biodiversity of the earth. [source] The cause of the travel troubleASTRONOMY & GEOPHYSICS, Issue 3 2010Article first published online: 24 MAY 2010 Satellite data have proved invaluable in tracking the continuing plume of ash from the volcanic eruption under Iceland's Eyjafjallajoekull glacier, which has caused intermittent closure of airspace in northern Europe since the eruption started on 20 March this year. [source] Can late summer Landsat data be used for locating Asian migratory locust, Locusta migratoria migratoria, oviposition sites in the Amudarya River delta, Uzbekistan?ENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 2 2008Ramesh Sivanpillai Abstract Existing survey methods for assessing the Asian migratory locust, Locusta migratoria migratoria L. (Orthoptera: Acrididae), infestation risk in the Amudarya River delta, Uzbekistan, are largely constrained by economic resources and site accessibility. The surveys are restricted to a few easily accessible areas, which leads to a misinterpretation of the threat of locust infestation. This often results in indiscriminate blanket treatments of vast areas of wetlands with broad-spectrum insecticides, which may adversely impact non-target fauna and flora. In order to minimize the bias during surveys, one approach would be to allocate the sampling locations based on the distribution of the primary food and shelter plant of the locusts, the common reed, Phragmites australis (Cav.) Trin. ex Steud (Poaceae). In this study, we evaluated the utility of satellite-based remotely sensed data (Landsat TM) acquired in August 2006 to characterize reed distribution in the delta and identify potential locust oviposition sites. The overall accuracy of the Landsat data to map land cover classes in the delta was 84%. The Landsat TM data identified 90% of the reeds, but it was less useful in identifying areas where other vegetations (shrubs and grasses) were mixed with reeds. During the following summer field survey in June 2007, we identified 37 sites that were infested with early-instar locusts. The low migration capacity of young nymphs in dense reed vegetation allowed us to presume that these sites were used for oviposition in the previous summer. Twenty-eight (74%) of these 37 sites had reeds in the previous year. Results from these studies demonstrate that reed distribution maps derived from satellite data could be used for targeting locust egg-pod survey locations, in order to minimize sampling bias while predicting locust infestation risks for the following season. [source] Global statistical analysis of MISR aerosol data: a massive data product from NASA's Terra satelliteENVIRONMETRICS, Issue 7 2007Tao Shi Abstract In climate models, aerosol forcing is the major source of uncertainty in climate forcing, over the industrial period. To reduce this uncertainty, instruments on satellites have been put in place to collect global data. However, missing and noisy observations impose considerable difficulties for scientists researching the global distribution of aerosols, aerosol transportation, and comparisons between satellite observations and global-climate-model outputs. In this paper, we fit a Spatial Mixed Effects (SME) statistical model to predict the missing values, denoise the observed values, and quantify the spatial-prediction uncertainties. The computations associated with the SME model are linear scalable to the number of data points, which makes it feasible to process massive global satellite data. We apply the methodology, which is called Fixed Rank Kriging (FRK), to the level-3 Aerosol Optical Depth (AOD) dataset collected by NASA's Multi-angle Imaging SpectroRadiometer (MISR) instrument flying on the Terra satellite. Overall, our results were superior to those from non-statistical methods and, importantly, FRK has an uncertainty measure associated with it that can be used for comparisons over different regions or at different time points. Copyright © 2007 John Wiley & Sons, Ltd. [source] Evaluating the impacts of climate and elevated carbon dioxide on tropical rainforests of the western Amazon basin using ecosystem models and satellite dataGLOBAL CHANGE BIOLOGY, Issue 1 2010HIROFUMI HASHIMOTO Abstract Forest inventories from the intact rainforests of the Amazon indicate increasing rates of carbon gain over the past three decades. However, such estimates have been questioned because of the poor spatial representation of the sampling plots and the incomplete understanding of purported mechanisms behind the increases in biomass. Ecosystem models, when used in conjunction with satellite data, are useful in examining the carbon budgets in regions where the observations of carbon flows are sparse. The purpose of this study is to explain observed trends in normalized difference vegetation index (NDVI) using climate observations and ecosystem models of varying complexity in the western Amazon basin for the period of 1984,2002. We first investigated trends in NDVI and found a positive trend during the study period, but the positive trend in NDVI was observed only in the months from August to December. Then, trends in various climate parameters were calculated, and of the climate variables considered, only shortwave radiation was found to have a corresponding significant positive trend. To compare the impact of each climate component, as well as increasing carbon dioxide (CO2) concentrations, on evergreen forests in the Amazon, we ran three ecosystem models (CASA, Biome-BGC, and LPJ), and calculated monthly net primary production by changing a climate component selected from the available climate datasets. As expected, CO2 fertilization effects showed positive trends throughout the year and cannot explain the positive trend in NDVI, which was observed only for the months of August to December. Through these simulations, we demonstrated that the positive trend in shortwave radiation can explain the positive trend in NDVI observed for the period from August to December. We conclude that the positive trend in shortwave radiation is the most likely driver of the increasing trend in NDVI and the corresponding observed increases in forest biomass. [source] Spring phenology in boreal Eurasia over a nearly century time scaleGLOBAL CHANGE BIOLOGY, Issue 3 2008NICOLAS DELBART Abstract It has been widely reported that tree leaves have tended to appear earlier in many regions of the northern hemisphere in the last few decades, reflecting climate warming. Satellite observations revealed an 8-day advance in leaf appearance date between 1982 and 1991 in northern latitudes. In situ observations show that leaf appearance dates in Europe have advanced by an average of 6.3 days from 1959 to 1996. Modelling of leaf appearance on the basis of temperature also shows a marked advance in temperate and boreal regions from 1955 to 2002. However, before 1955, reported studies of phenological variations are restricted to local scale. Modelling, ground observations and satellite observations are here combined to analyse phenological variations in Eurasian taiga over nearly a century. The trend observed by remote sensing consists mainly in a shift at the end of the 1980s, reflecting a shift in winter and spring temperature. In western boreal Eurasia, a trend to earlier leaf appearance is evident since the mid-1930s, although it is discontinuous. In contrast, the strong advance in leaf appearance detected over Central Siberia using satellite data in 1982,1991 is strengthened by late springs in 1983,1984; moreover, in this region the green-up timing has displayed successive trends with opposite signs since 1920. Thus, such strong trend is not unusual if considered locally. However, the recent advance is unique in simultaneously affecting most of the Eurasian taiga, the leaf appearance dates after 1990 being the earliest in nearly a century in most of the area. [source] Comparison of phenology trends by land cover class: a case study in the Great Basin, USAGLOBAL CHANGE BIOLOGY, Issue 2 2008BETHANY A. BRADLEY Abstract Direct impacts of human land use and indirect impacts of anthropogenic climate change may alter land cover and associated ecosystem function, affecting ecological goods and services. Considerable work has been done to identify long-term global trends in vegetation greenness, which is associated with primary productivity, using remote sensing. Trend analysis of satellite observations is subject to error, and ecosystem change can be confused with interannual variability. However, the relative trends of land cover classes may hold clues about differential ecosystem response to environmental forcing. Our aim was to identify phenological variability and 10-year trends for the major land cover classes in the Great Basin. This case study involved two steps: a regional, phenology-based land cover classification and an identification of phenological variability and 10-year trends stratified by land cover class. The analysis used a 10-year time series of Advanced Very High Resolution Radiometer satellite data to assess regional scale land cover variability and identify change. The phenology-based regional classification was more detailed and accurate than national or global products. Phenological variability over the 10-year period was high, with substantial shifts in timing of start of season of up to 9 weeks. The mean long-term trends of montane land cover classes were significantly different from valley land cover classes due to a poor response of montane shrubland and pinyon-juniper woodland to the early 1990s drought. The differential response during the 1990s suggests that valley ecosystems may be more resilient and montane ecosystems more susceptible to prolonged drought. This type of regional-scale land cover analysis is necessary to characterize current patterns of land cover phenology, distinguish between anthropogenically driven land cover change and interannual variability, and identify ecosystems potentially susceptible to regional and global change. [source] Site-level evaluation of satellite-based global terrestrial gross primary production and net primary production monitoringGLOBAL CHANGE BIOLOGY, Issue 4 2005David P. Turner Abstract Operational monitoring of global terrestrial gross primary production (GPP) and net primary production (NPP) is now underway using imagery from the satellite-borne Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. Evaluation of MODIS GPP and NPP products will require site-level studies across a range of biomes, with close attention to numerous scaling issues that must be addressed to link ground measurements to the satellite-based carbon flux estimates. Here, we report results of a study aimed at evaluating MODIS NPP/GPP products at six sites varying widely in climate, land use, and vegetation physiognomy. Comparisons were made for twenty-five 1 km2 cells at each site, with 8-day averages for GPP and an annual value for NPP. The validation data layers were made with a combination of ground measurements, relatively high resolution satellite data (Landsat Enhanced Thematic Mapper Plus at ,30 m resolution), and process-based modeling. There was strong seasonality in the MODIS GPP at all sites, and mean NPP ranged from 80 g C m,2 yr,1 at an arctic tundra site to 550 g C m,2 yr,1 at a temperate deciduous forest site. There was not a consistent over- or underprediction of NPP across sites relative to the validation estimates. The closest agreements in NPP and GPP were at the temperate deciduous forest, arctic tundra, and boreal forest sites. There was moderate underestimation in the MODIS products at the agricultural field site, and strong overestimation at the desert grassland and at the dry coniferous forest sites. Analyses of specific inputs to the MODIS NPP/GPP algorithm , notably the fraction of photosynthetically active radiation absorbed by the vegetation canopy, the maximum light use efficiency (LUE), and the climate data , revealed the causes of the over- and underestimates. Suggestions for algorithm improvement include selectively altering values for maximum LUE (based on observations at eddy covariance flux towers) and parameters regulating autotrophic respiration. [source] Net changes in regional woody vegetation cover and carbon storage in Texas Drylands, 1937,1999GLOBAL CHANGE BIOLOGY, Issue 3 2003GREGORY P. ASNER Abstract Although local increases in woody plant cover have been documented in arid and semiarid ecosystems worldwide, there have been few long-term, large-scale analyses of changes in woody plant cover and aboveground carbon (C) stocks. We used historical aerial photography, contemporary Landsat satellite data, field observations, and image analysis techniques to assess spatially specific changes in woody vegetation cover and aboveground C stocks between 1937 and 1999 in a 400-km2 region of northern Texas, USA. Changes in land cover were then related to topo-edaphic setting and historical land-use practices. Mechanical or chemical brush management occurred over much of the region in the 1940,1950s. Rangelands not targeted for brush management experienced woody cover increases of up to 500% in 63 years. Areas managed with herbicides, mechanical treatments or fire exhibited a wide range of woody cover changes relative to 1937 (,75% to + 280%), depending on soil type and time since last management action. At the integrated regional scale, there was a net 30% increase in woody plant cover over the 63-year period. Regional increases were greatest in riparian corridors (33%) and shallow clay uplands (26%) and least on upland clay loams (15%). Allometric relationships between canopy cover and aboveground biomass were used to estimate net aboveground C storage changes in upland (nonriparian) portions of regional landscapes. Carbon stocks increased from 380 g C m,2 in 1937 to 500 g C m,2 in 1999, a 32% net increase across the 400 km2 region over the 63-year period. These plant C storage change estimates are highly conservative in that they did not include the substantial increases in woody plant cover observed within riparian landscape elements. Results are discussed in terms of implications for ,carbon accounting' and the global C cycle. [source] Spatial and temporal variability of the phenological seasons in Germany from 1951 to 1996GLOBAL CHANGE BIOLOGY, Issue 6 2001Annette Menzel Abstract Various indications for shifts in plant and animal phenology resulting from climate change have been observed in Europe. This analysis of phenological seasons in Germany of more than four decades (1951,96) has several major advantages: (i) a wide and dense geographical coverage of data from the phenological network of the German Weather Service, (ii) the 16 phenophases analysed cover the whole annual cycle and, moreover, give a direct estimate of the length of the growing season for four deciduous tree species. After intensive data quality checks, two different methods ,,linear trend analyses and comparison of averages of subintervals , were applied in order to determine shifts in phenological seasons in the last 46 years. Results from both methods were similar and reveal a strong seasonal variation. There are clear advances in the key indicators of earliest and early spring (,0.18 to ,0.23 d y,1) and notable advances in the succeeding spring phenophases such as leaf unfolding of deciduous trees (,0.16 to ,0.08 d y,1). However, phenological changes are less strong during autumn (delayed by +,0.03 to +,0.10 d y,1 on average). In general, the growing season has been lengthened by up to ,0.2 d y,1 (mean linear trends) and the mean 1974,96 growing season was up to 5 days longer than in the 1951,73 period. The spatial variability of trends was analysed by statistical means and shown in maps, but these did not reveal any substantial regional differences. Although there is a high spatial variability, trends of phenological phases at single locations are mirrored by subsequent phases, but they are not necessarily identical. Results for changes in the biosphere with such a high resolution with respect to time and space can rarely be obtained by other methods such as analyses of satellite data. [source] Fire regimes of China: inference from statistical comparison with the United StatesGLOBAL ECOLOGY, Issue 5 2009Meg A. Krawchuk ABSTRACT Aim, Substantial overlap in the climate characteristics of the United States and China results in similar land-cover types and weather conditions, especially in the eastern half of the two countries. These parallels suggest similarities in fire regimes as well, yet relatively little is known about the historical role of fire in Chinese ecosystems. Consequently, we aimed to infer fire regime characteristics for China based on our understanding of climate,fire relationships in the United States. Location, The conterminous United States and the People's Republic of China. Methods, We used generalized additive models to quantify the relationship between reference fire regime classes adopted by the LANDFIRE initiative in the United States, and a global climate data set. With the models, we determined which climate variables best described the distribution of fire regimes in the United States then used these models to predict the spatial distribution of fire regimes in China. The fitted models were validated quantitatively using receiver operating characteristic area under the curve (AUC). We validated the predicted fire regimes in China by comparison with palaeoecological fire data and satellite-derived estimates of current fire activity. Results, Quantitative validation using the AUC indicated good discrimination of the distribution of fire regimes by models for the United States. Overall, fire regimes with more frequent return intervals were more likely in the east than in the west. The resolution of available historical and prehistorical fire data for China, including sediment cores, allowed only coarse, qualitative validation, but provided supporting evidence that fire has long been a part of ecosystem function in eastern China. MODIS satellite data illustrated that fire frequency within the last decade supported the classification of much of western China as relatively fire-free; however, much of south-eastern China experiences more fire activity than predicted with our models, probably as a function of the extensive use of fire by people. Conclusions, While acknowledging there are many cultural, environmental and historical differences between the United States and China, our fire regime models based on climate data demonstrate potential historical fire regimes for China, and propose that large areas of China share historical fire,vegetation,climate complexes with the United States. [source] The greening and browning of Alaska based on 1982,2003 satellite dataGLOBAL ECOLOGY, Issue 4 2008David Verbyla Abstract Aim To examine the trends of 1982,2003 satellite-derived normalized difference vegetation index (NDVI) values at several spatial scales within tundra and boreal forest areas of Alaska. Location Arctic and subarctic Alaska. Methods Annual maximum NDVI data from the twice monthly Global Inventory Modelling and Mapping Studies (GIMMS) NDVI 1982,2003 data set with 64-km2 pixels were extracted from a spatial hierarchy including three large regions: ecoregion polygons within regions, ecozone polygons within boreal ecoregions and 100-km climate station buffers. The 1982,2003 trends of mean annual maximum NDVI values within each area, and within individual pixels, were computed using simple linear regression. The relationship between NDVI and temperature and precipitation was investigated within climate station buffers. Results, At the largest spatial scale of polar, boreal and maritime regions, the strongest trend was a negative trend in NDVI within the boreal region. At a finer scale of ecoregion polygons, there was a strong positive NDVI trend in cold arctic tundra areas, and a strong negative trend in interior boreal forest areas. Within boreal ecozone polygons, the weakest negative trends were from areas with a maritime climate or colder mountainous ecozones, while the strongest negative trends were from warmer basin ecozones. The trends from climate station buffers were similar to ecoregion trends, with no significant trends from Bering tundra buffers, significant increasing trends among arctic tundra buffers and significant decreasing trends among interior boreal forest buffers. The interannual variability of NDVI among the arctic tundra buffers was related to the previous summer warmth index. The spatial pattern of increasing tundra NDVI at the pixel level was related to the west-to-east spatial pattern in changing climate across arctic Alaska. There was no significant relationship between interannual NDVI and precipitation or temperature among the boreal forest buffers. The decreasing NDVI trend in interior boreal forests may be due to several factors including increased insect/disease infestations, reduced photosynthesis and a change in root/leaf carbon allocation in response to warmer and drier growing season climate. Main conclusions There was a contrast in trends of 1982,2003 annual maximum NDVI, with cold arctic tundra significantly increasing in NDVI and relatively warm and dry interior boreal forest areas consistently decreasing in NDVI. The annual maximum NDVI from arctic tundra areas was strongly related to a summer warmth index, while there were no significant relationships in boreal areas between annual maximum NDVI and precipitation or temperature. Annual maximum NDVI was not related to spring NDVI in either arctic tundra or boreal buffers. [source] Potential for Satellite Remote Sensing of Ground WaterGROUND WATER, Issue 2 2006Matthew W. Becker Predicting hydrologic behavior at regional scales requires heterogeneous data that are often prohibitively expensive to acquire on the ground. As a result, satellite-based remote sensing has become a powerful tool for surface hydrology. Subsurface hydrology has yet to realize the benefits of remote sensing, even though surface expressions of ground water can be monitored from space. Remotely sensed indicators of ground water may provide important data where practical alternatives are not available. The potential for remote sensing of ground water is explored here in the context of active and planned satellite-based sensors. Satellite technology is reviewed with respect to its ability to measure ground water potential, storage, and fluxes. It is argued here that satellite data can be used if ancillary analysis is used to infer ground water behavior from surface expressions. Remotely sensed data are most useful where they are combined with numerical modeling, geographic information systems, and ground-based information. [source] Estimation of rainfall from infrared-microwave satellite data for basin-scale hydrologic modellingHYDROLOGICAL PROCESSES, Issue 15 2010Oscar Anthony Kalinga Abstract The infrared-microwave rainfall algorithm (IMRA) was developed for retrieving spatial rainfall from infrared (IR) brightness temperatures (TBs) of satellite sensors to provide supplementary information to the rainfall field, and to decrease the traditional dependency on limited rain gauge data that are point measurements. In IMRA, a SLOPE technique (ST) was developed for discriminating rain/no-rain pixels through IR image cloud-top temperature gradient, and 243K as the IR threshold temperature for minimum detectable rainfall rate. IMRA also allows for the adjustment of rainfall derived from IR-TB using microwave (MW) TBs. In this study, IMRA rainfall estimates were assessed on hourly and daily basis for different spatial scales (4, 12, 20, and 100 km) using NCEP stage IV gauge-adjusted radar rainfall data, and daily rain gauge data. IMRA was assessed in terms of the accuracy of the rainfall estimates and the basin streamflow simulated by the hydrologic model, Sacramento soil moisture accounting (SAC-SMA), driven by the rainfall data. The results show that the ST option of IMRA gave accurate satellite rainfall estimates for both light and heavy rainfall systems while the Hessian technique only gave accurate estimates for the convective systems. At daily time step, there was no improvement in IR-satellite rainfall estimates adjusted with MW TBs. The basin-scale streamflow simulated by SAC-SMA driven by satellite rainfall data was marginally better than when SAC-SMA was driven by rain gauge data, and was similar to the case using radar data, reflecting the potential applications of satellite rainfall in basin-scale hydrologic modelling. Copyright © 2010 John Wiley & Sons, Ltd. [source] Application of the WEPP model for prioritization and evaluation of best management practices in an Indian watershedHYDROLOGICAL PROCESSES, Issue 21 2009A. Pandey Abstract The pre-calibrated and validated physically based watershed model, water erosion prediction project (WEPP) was used as a modelling tool for the identification of critical watersheds and evaluation of best management practices for a small hilly watershed (Karso) of India. The land use/cover of the study area was generated using IRS-1C LISS-III (linear imaging self scanner) satellite data. The watershed and sub-watershed boundaries, drainage, slope and soil map of the study area were generated using ARC/INFO geographic information system (GIS). The WEPP model was finally applied to the Karso watershed which lies within Damodar Barakar catchment of India to identify the critical sub-watersheds on the basis of their simulated average annual sediment yields. Priorities were fixed on the basis of ranks assigned to each critical sub-watershed based on the susceptibility to erosion. The sub-watershed having the highest sediment yield was assigned a priority number 1, the next highest value was assigned a priority number 2, and so on. Subsequently, the model was used for evaluating the effectiveness of best management practices (crop and tillage) for conservation of soil for all the sub-watersheds. On the basis of this study, it is realized that cash crops like soyabean should be encouraged in the upland portion of the sub-watersheds, and the existing tillage practice (country plough/mould board plough) may be replaced by a field cultivation system for conservation of soil and water in the sub-watersheds. Copyright © 2009 John Wiley & Sons, Ltd. [source] UNEP-GEMS/Water Programme,water quality data, GEMStat and open web services,and Japanese cooperationHYDROLOGICAL PROCESSES, Issue 9 2007Sabrina Barker Abstract The purpose of this paper is threefold. First, it demonstrates how monitoring stations that collect water quality data can be situated globally via satellite data from Google Earth. Important technical issues such as interoperability and Open Web Services are discussed in this context. Second, it illustrates how researchers at local levels can benefit from this global technology. The discussion draws from the online water quality database, GEMStat, which contains water quality data and sediment load calculations from around the world. These types of data, collected locally, can be shown to bear global implications through Internet technology. GEMStat has been expanded to include Open Web Services to enable interoperability with other online databases. Third, it illustrate an international framework of cooperation through GEMS/Water Japan, introducing on-site monitoring activities as well as management of international river basin (Mekong/La Plata). Considerations for future application framework are presented in conclusion. Copyright © 2007 John Wiley & Sons, Ltd. [source] Modelling snowpack surface temperature in the Canadian Prairies using simplified heat flow modelsHYDROLOGICAL PROCESSES, Issue 18 2005Purushottam Raj Singh Abstract Three practical schemes for computing the snow surface temperature Ts, i.e. the force,restore method (FRM), the surface conductance method (SCM), and the Kondo and Yamazaki method (KYM), were assessed with respect to Ts retrieved from cloud-free, NOAA-AVHRR satellite data for three land-cover types of the Paddle River basin of central Alberta. In terms of R2, the mean Ts, the t -test and F -test, the FRM generally simulated more accurate Ts than the SCM and KYM. The bias in simulated Ts is usually within several degrees Celsius of the NOAA-AVHRR Ts for both the calibration and validation periods, but larger errors are encountered occasionally, especially when Ts is substantially above 0 °C. Results show that the simulated Ts of the FRM is more consistent than that of the SCM, which in turn was more consistent than that of the KYM. This is partly because the FRM considers two aspects of heat conduction into snow, a stationary-mean diurnal (sinusoidal) temperature variation at the surface coupled to a near steady-state ground heat flux, whereas the SCM assumes a near steady-state, simple heat conduction, and other simplifying assumptions, and the KYM does not balance the snowpack heat fluxes by assuming the snowpack having a vertical temperature profile that is linear. Copyright © 2005 John Wiley & Sons, Ltd. [source] Global atmospheric energetics from NCEP,Reanalysis 2 and ECMWF,ERA40 ReanalysisINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 2 2009Carlos A. F. Marques Abstract The global atmospheric energy cycle is estimated on an annual basis using Reanalysis 2 data from the National Centers for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR), and ERA 40 Reanalyses from the European Centre for Medium-Range Weather Forecasts (ECMWF) for the period 1979,2001. A formalism to avoid belowground data on pressure levels intercepted by topography is adopted. No appreciable differences were found between the two datasets from the energetics point of view. The so-called ,, and v·grad z formulations were both used for the conversions from zonal available potential energy into zonal kinetic energy (CZ) and from eddy available potential energy into eddy kinetic energy (CE). Results with both formulations are comparable only when using the formalism preventing belowground data to enter into the computations. Atmospheric energetics are also computed using ECMWF Reanalyses for the period 1958,1978. A significant increase was found in the eddy kinetic and eddy available potential energies from the early period to the later period, likely related to the assimilation in the reanalyses of satellite data after 1979. The conversion rate, CZ, was found to change its sign throughout the years. The atmospheric energy cycle using the ECMWF Reanalyses data is compared with five previous estimates. Differences in the direction of the conversion rate, CZ, between the various estimates may be explained by the different time periods chosen for averaging. Owing to the omission of belowground data, the conversion from zonal available potential energy into eddy available potential energy (CA) was somewhat smaller in ECMWF Reanalyses than in the previous estimates. Despite those differences, an overall agreement may be found between the various estimates for the atmospheric energy cycle. Copyright © 2008 Royal Meteorological Society [source] Variability in sea-surface temperature and winds in the tropical south-east Atlantic Ocean and regional rainfall relationshipsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 1 2009J. C. Hermes Abstract Variability in sea-surface temperature (SST) and winds in the Angola Benguela frontal zone (ABFZ) in the tropical south-east Atlantic Ocean has previously been shown to be important for regional fisheries and for seasonal rainfall anomalies over Angola/Namibia in austral summer and coastal West Africa in boreal summer. This study investigates intraseasonal variability in winds and SST over this region using QuikSCAT and tropical rainfall measuring mission (TRMM) satellite data for 1999,2004. Wavelet analyses reveal periods of relatively strong power in the 20,30 or 30,64 day frequency bands throughout the record but that there is substantial interannual variability in the occurrence of these intraseasonal oscillations. The implications of this variability for seasonal rainfall anomalies during the main rainy seasons in southern Africa (austral summer) and coastal West Africa (boreal summer) are discussed. Copyright © 2008 Royal Meteorological Society [source] Radiosonde temperature trends and their uncertainties over eastern China,INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 10 2008Yanjun Guo Abstract Trends and uncertainty in radiosonde temperature records for six sample stations in eastern China are assessed. Results from a complex approach using metadata and a two-phase regression (M-TPR) to capture known and unknown metadata events respectively are compared with an ensemble of possible solutions generated by the Met Office automated homogenization system (QUARC). Independent satellite records from the Microwave Sounding Unit (MSU) record are used to validate breakpoints over the satellite era. Differences in the treatment of metadata and the strictness of the statistical breakpoint detection methods used lead to relatively poor agreement in breakpoint identification. Agreement in long-term (1958,2003) trends in the homogenized data was found to result from a fortuitous cancellation of large differences in the pre- and post-satellite era trends between the two approaches. A consideration of independent MSU satellite data lends some credence to the presence and calculated magnitude of many of the assigned breakpoints that were not associated with recorded metadata events, in the later part of the record. However, it also highlights that neither of the approaches is likely to be perfect at identifying breaks. Improved metadata are likely to prove vital in confirming the presence of these breaks and hence the veracity of the various homogenization approaches to data for eastern China. Copyright © 2007 Royal Meteorological Society [source] Interannual variability of the tropical Atlantic independent of and associated with ENSO: Part I. The North Tropical AtlanticINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 14 2006Itsuki C. Handoh Abstract The interannual variability of the tropical Atlantic ocean,atmosphere system is examined using 50 years of sea-surface temperature (SST) and re-analysis data, and satellite data when available. A singular value decomposition analysis of 12- to 72-month bandpass filtered SST and zonal wind stress reveals two dominant modes of interannual variability. The SST anomalies are confined to the North Tropical Atlantic (NTA) in the first mode and extend over the equatorial and South Tropical Atlantic in the second mode. No evidence is found for an Atlantic SST dipole. The structure of the first (NTA) mode is examined in detail here, while the second mode has been described in a companion paper. In particular, the relationship of the NTA mode with El Niño,Southern Oscillation (ENSO) is investigated. There are 12 NTA events (seven warm and five cold) that are associated with ENSO, and 18 NTA events (seven warm and 11 cold) that are independent of ENSO. The ENSO-associated NTA events appear to be a passive response to remote ENSO forcing, mainly via a Pacific-North America (PNA)-like wave train that induces SST anomalies over the NTA through changes in the surface wind and latent heat flux. The NTA anomalies peak four months after ENSO. There does not appear to be an atmospheric response to the NTA SST anomalies as convection over the Atlantic is suppressed by the anomalous Walker circulation due to ENSO. The ENSO-independent NTA events also appear to be induced by an extratropical wave train from the Pacific sector (but one that is independent of Pacific SST), and forcing by the North Atlantic Oscillation (NAO) also contributes. As the event matures, the atmosphere does respond to the NTA SST anomalies, with enhanced convection over the Caribbean and a wave train that propagates northeastward to Europe. Copyright © 2006 Royal Meteorological Society [source] Long-term changes in ozone mini-hole event frequency over the Northern Hemisphere derived from ground-based measurementsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 12 2002Janusz W. Krzy Abstract Decadal changes of ozone mini-hole event appearance over the Northern Hemisphere midlatitudes are examined based on daily total ozone data from seven stations having long records (four decades or more) of ozone observations. The various threshold methods for accepting and rejecting the ozone minima as mini-holes are examined. Mini-hole event activity is seen to be rather stable when averaged over a decadal time scale if the mini-holes are selected as large negative departures (exceeding 20%) relative to the moving long-term total ozone reference. The results are compared with a previous ozone mini-hole climatology derived from satellite data (TOMS measurements on board the Nimbus-7 satellite for the period 1978,93). A nonlinear statistical model (MARS), which takes into account various total ozone dynamical proxies (from NCEP,NCAR reanalysis), is used to study dynamical factors responsible for the ozone extremes over Arosa in the period 1950,99. The model explains as much as 95% of the total variance of the ozone extremes. The model,observation differences averaged over the decadal intervals are rather smooth throughout the whole period analysed. It is suggested that the short-term dynamical processes controlling the appearance of ozone extremes influenced the ozone field in a similar way before and after the onset of abrupt ozone depletion in the early 1980s. The analysis of the ozone profile and the tropopause pressure (from the ozonesondings over Hohenpeissenberg, 1966,99) during mini-hole events shows ,60% ozone reduction in the lower stratosphere and an approximately 50 hPa upward shift of the thermal tropopause there. Copyright © 2002 Royal Meteorological Society. [source] Dynamic fade restoration in Ka-band satellite systemsINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 4 2002A. Paraboni Atmospheric precipitation can seriously affect the propagation of centimeter and millimeter electromagnetic waves. As a consequence, in some applications, it is necessary to make use of a fade countermeasure technique in order to satisfy the system availability and quality requirements. This study analyses the performance of a satellite-based system in geo-stationary orbit operating at 20 GHz, dynamically assigning the antenna directivity pattern to counteract tropospheric attenuation. The on-board power is spatially distributed over the covered region to minimize, at any time, the number of users undergoing outage because of the tropospheric attenuation. Both the aspects of broadcasting and telecommunication services are addressed. The reflector antenna of the system is supposed to be illuminated by a cluster of feeds driven by a set of excitation coefficients, continuously modified and optimized according to the meteorological information derived by processing METEOSAT satellite data and ECMWF (European Centre for Medium-Range Weather Forecasts) data. Copyright © 2002 John Wiley & Sons, Ltd. [source] Leaf green-up in a semi-arid African savanna -separating tree and grass responses to environmental cuesJOURNAL OF VEGETATION SCIENCE, Issue 4 2007S. Archibald Abstract Question: Can satellite time series be used to identify tree and grass green-up dates in a semi-arid savanna system, and are there predictable environmental cues for green-up for each life form? Location: Acacia nigrescens /Combretum apiculatum savanna, Kruger National Park, South Africa (25° S, 31° E). Methods: Remotely-sensed data from the MODIS sensor were used to provide a five year record of greenness (NDVI) between 2000 and 2005. The seasonal and inter-annual patterns of leaf display of trees and grasses were described, using additional ecological information to separate the greening signal of each life form from the satellite time series. Linking this data to daily meteorological and soil moisture data allowed the cues responsible for leaf flush in trees and grasses to be identified and a predictive model of savanna leaf-out was developed. This was tested on a 22-year NDVI dataset from the Advanced Very High Resolution Radiometer. A day length cue for tree green-up predicted 86% of the green-ups with an accuracy better than one month. A soil moisture and day length cue for grass green-up predicted 73% of the green-ups with an accuracy better than a month, and 82% within 45 days. This accuracy could be improved if the temporal resolution of the satellite data was shortened from the current two weeks. Conclusions: The data show that at a landscape scale savanna trees have a less variable phenological cycle (within and between years) than grasses. Realistic biophysical models of savanna systems need to take this into account. Using climatic data to predict these dynamics is a feasible approach. [source] Remote sensing of protected areas to derive baseline vegetation functioning characteristicsJOURNAL OF VEGETATION SCIENCE, Issue 5 2004Martín F. Garbulsky Abstract: Question: How can we derive baseline/reference situations to evaluate the impact of global change on terrestrial ecosystem functioning? Location: Main biomes (steppes to rain forests) of Argentina. Methods: We used AVHRR/NOAA satellite data to characterize vegetation functioning. We used the seasonal dynamics of the Normalized Difference Vegetation Index (NDVI), a linear estimator of the fraction of the photosynthetic active radiation intercepted by vegetation (fPAR), and the surface temperature (Ts), for the period 1981,1993. We extracted the following indices: NDVI integral (NDVI -I), NDVI relative range (Rrel), NDVI maximum value (Vmax), date of maximum NDVI (Dmax) and actual evapotranspiration. Results: fPAR varied from 2 to 80%, in relation to changes in net primary production (NPP) from 83 to 1700 g.m- 2.yr -1. NDVI -I, Vmax and fPAR had positive, curvilinear relationships to mean annual precipitation (MAP), NPP was linearly related to MAP. Tropical and subtropical biomes had a significantly lower seasonality (Rrel) than temperate ones. Dmax was not correlated with the defined environmental gradients. Evapotranspiration ranged from 100 to 1100 mm.yr -1. Interannual variability of NDVI attributes varied across the temperature and precipitation gradients. Conclusions: Our results may be used to represent baseline conditions in evaluating the impact of land use changes across environmental gradients. The relationships between functional attributes and environmental variables provide a way to extrapolate ecological patterns from protected areas across modified habitats and to generate maps of ecosystem functioning. [source] Discriminating raining from non-raining cloud areas at mid-latitudes using meteosat second generation SEVIRI night-time dataMETEOROLOGICAL APPLICATIONS, Issue 2 2008B. Thies Abstract A new method for the delineation of precipitation during night-time using multispectral satellite data is proposed. The approach is not only applicable to the detection of mainly convective precipitation by means of the commonly used relation between infrared cloud-top temperature and rainfall probability but enables also the detection of stratiform precipitation (e.g. in connection with mid-latitude frontal systems). The presented scheme is based on the conceptual model that precipitating clouds are characterized by a combination of particles large enough to fall, an adequate vertical extension [both represented by the cloud water path (CWP)], and the existence of ice particles in the upper part of the cloud. As no operational retrieval exists for Meteosat Second Generation (MSG) to compute the CWP during night-time, suitable combinations of brightness temperature differences (,T) between the thermal bands of Meteosat Second Generation-Spinning Enhanced Visible and InfraRed Imager (MSG SEVIRI, ,T3.9,10.8, ,T3.9,7.3, ,T8.7,10.8, ,T10.8,12.1) are used to infer implicit information about the CWP and to compute a rainfall confidence level. ,T8.7,10.8 and ,T10.8,12.1 are particularly considered to supply information about the cloud phase. Rain area delineation is realized by using a minimum threshold of the rainfall confidence. To obtain a statistical transfer function between the rainfall confidence and the channel differences, the value combination of the channel differences is compared with ground-based radar data. The retrieval is validated against independent radar data not used for deriving the transfer function and shows an encouraging performance as well as clear improvements compared to existing optical retrieval techniques using only IR thresholds for cloud-top temperature. Copyright © 2008 Royal Meteorological Society [source] Astronomical site selection: on the use of satellite data for aerosol content monitoringMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2008A. M. Varela ABSTRACT The main goal of this work is to analyse new approaches to the study of the properties of astronomical sites. In particular, satellite data measuring aerosols have recently been proposed as a useful technique for site characterization and searching for new sites to host future very large telescopes. Nevertheless, these data need to be critically considered and interpreted in accordance with the spatial resolution and spectroscopic channels used. In this paper, we have explored and retrieved measurements from satellites with high spatial and temporal resolutions and concentrated on channels of astronomical interest. The selected data sets are the Ozone Monitoring Instrument on board the NASA Aura satellite and the Moderate Resolution Imaging Spectroradiometer on board the NASA Terra and Aqua satellites. A comparison of remote-sensing and in situ techniques is discussed. As a result, we find that aerosol data provided by satellites up to now are not reliable enough for aerosol site characterization, and in situ data are required. [source] | ||||||||||||||||||||||||||||||||||