The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
James J. Simpson - One of the best experts on this subject based on the ideXlab platform.
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A recurrent neural network classifier for improved retrievals of Areal Extent of snow cover
IEEE Transactions on Geoscience and Remote Sensing, 2001Co-Authors: James J. Simpson, T.j. McintireAbstract:Accurate detection of Areal Extent of snow in mountainous regions is important. Areal Extent of snow is a useful climatic indicator. Moreover, snow melt is a major source of water supply for many arid regions (e.g., western United States, Morocco) and affects regional ecosystems. Unfortunately, accurate satellite retrievals of Areal Extent of snow have been difficult to achieve. Two approaches to effectively and accurately detect clear land, cloud, and Areal Extent of snow in satellite data are developed. A feed-forward neural network (FFNN) is used to classify individual images, and a recurrent NN is used to classify sequences of images. The continuous outputs of the NN, combined with a linear mixing model, provide support for mixed-pixel classification. Validation with independent in situ data confirms the classification accuracy (94% for feed-forward NN, 97% for recurrent NN). The combination of rapid temporal sampling (e.g., GOES) and a recurrent NN classifier is recommended (relative to an isolated scene (e.g., AVHRR) and a feed-forward NN classifier).
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Improved estimates of the Areal Extent of snow cover from AVHRR data
Journal of Hydrology, 1998Co-Authors: James J. Simpson, J.r. Stitt, M. SienkoAbstract:Satellite data provide the only practical way to obtain the necessary spatial and temporal coverage of Areal Extent of snow cover required for hydrometeorological applications. A new procedure has been developed which: (1) accurately separates snow and cloud from clear land in a terrestrial scene; and (2) uses other criteria to separate both cold, high clouds and warm, low clouds from snow. A mixed pixel class is also identified and pixels in this class can be assigned a percentage composition (cloud, snow, and land) using a linear mixing model. The procedure has been ground-truthed with both Landsat data and SNOTEL (SNOwTELemetry) observations. Classification skill, based on a statistical comparison with SNOTEL observations, is about 97%. Application of the procedure to a wide variety of terrestrial environments is demonstrated.
Jeanfrancois Cretaux - One of the best experts on this subject based on the ideXlab platform.
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grace water storage estimates for the middle east and other regions with significant reservoir and lake storage
Hydrology and Earth System Sciences, 2012Co-Authors: Laurent Longuevergne, Clark R Wilson, Bridget R Scanlon, Jeanfrancois CretauxAbstract:While GRACE (Gravity Recovery and Climate Experiment) satellites are increasingly being used to moni- tor total water storage (TWS) changes globally, the impact of spatial distribution of water storage within a basin is gen- erally ignored but may be substantial. In many basins, wa- ter is often stored in reservoirs or lakes, flooded areas, small aquifer systems, and other localized regions with areas typ- ically below GRACE resolution ( 200 000 km 2 ). The ob- jective of this study was to assess the impact of nonuni- form water storage distribution on GRACE estimates of TWS changes as basin-wide averages, focusing on surface water reservoirs and using a priori information on reservoir storage from radar altimetry. Analysis included numerical experiments testing effects of location and Areal Extent of the localized mass (reservoirs) within a basin on basin-wide average water storage changes, and application to the lower Nile (Lake Nasser) and Tigris- Euphrates basins as examples. Numerical experiments show that by assuming uniform mass distribution, GRACE esti- mates may under- or overestimate basin-wide average water storage by up to a factor of 2, depending on reservoir loca- tion and Areal Extent. Although reservoirs generally cover less than 1 % of the basin area, and their spatial Extent may be unresolved by GRACE, reservoir storage may dominate water storage changes in some basins. For example, reservoir storage ac- counts for 95 % of seasonal water storage changes in the lower Nile and 10 % in the Tigris-Euphrates. Because reser- voirs are used to mitigate droughts and buffer against cli-
M. Sienko - One of the best experts on this subject based on the ideXlab platform.
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Improved estimates of the Areal Extent of snow cover from AVHRR data
Journal of Hydrology, 1998Co-Authors: James J. Simpson, J.r. Stitt, M. SienkoAbstract:Satellite data provide the only practical way to obtain the necessary spatial and temporal coverage of Areal Extent of snow cover required for hydrometeorological applications. A new procedure has been developed which: (1) accurately separates snow and cloud from clear land in a terrestrial scene; and (2) uses other criteria to separate both cold, high clouds and warm, low clouds from snow. A mixed pixel class is also identified and pixels in this class can be assigned a percentage composition (cloud, snow, and land) using a linear mixing model. The procedure has been ground-truthed with both Landsat data and SNOTEL (SNOwTELemetry) observations. Classification skill, based on a statistical comparison with SNOTEL observations, is about 97%. Application of the procedure to a wide variety of terrestrial environments is demonstrated.
Duncan M Fitzgerald - One of the best experts on this subject based on the ideXlab platform.
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assessing the response of the great marsh to sea level rise migration submersion or survival
Marine Geology, 2020Co-Authors: Sarah Farron, Zoe J Hughes, Duncan M FitzgeraldAbstract:Abstract To survive rising sea level, salt marshes must accrete vertically, migrate laterally, or undergo a combination of the two. If sufficient sediment is available for marsh accretion, the slope of the surrounding area is relatively flat, and edge erosion is minimal, then a marsh can theoretically maintain its Areal Extent through a combination of vertical accretion and upland expansion. However, in cases where sediment supply is limited and the marsh is backed by steeper slopes, it is unclear whether accretion and inland migration will be sufficient to counteract the combined effects of rising sea level and edge erosion. Given these barriers to marsh expansion, inland migration may not be a viable solution to marsh vulnerability to sea-level rise. We quantify the potential changes in Areal Extent under future sea-level rise scenarios for the Great Marsh in northern Massachusetts, where the marsh has a limited suspended sediment supply and relatively steep upland topography. Salt marsh is identified and classified into low or high marsh using LiDAR elevation and validated using aerial photography and vegetation surveys. We generate a simple 1D-H model using locally-measured accretion rates and their relationship to marsh elevation, to determine change in elevation and dominant plant species over time. A maximum inorganic sediment available to the marsh is prescribed for certain model scenarios to test the impact of sediment limitation. This limit is calculated based on the volumetric contribution of mineral sediment to the present marsh accretion rates. Predicted changes in marsh area over a 100-year model period are determined using the surrounding elevation gradients, calculated sediment availability, projected edge erosion, and local rates of sea-level rise (SLR). The two Representative Concentration Pathway (RCP) SLR scenarios used are based on the most recent IPCC report and also include the latest information concerning responses to ice sheet melting in Greenland and Antarctica. We find that as the rate of sea-level rise increases, the Areal Extent of the marsh decreases due to a lack of the suspended sediment needed to maintain marsh surface elevation and the inability of the marsh to encroach upon steep upland slopes. By comparing a model assuming constant accretion rates to one with mineral sediment-limited accretion, we find that when sediment if limited, marsh habitat conversion and loss occur earlier and more rapidly.
Claire L Parkinson - One of the best experts on this subject based on the ideXlab platform.
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Changes in the Areal Extent of Arctic Sea Ice: Observations from Satellites
2000Co-Authors: Claire L ParkinsonAbstract:Wintertime sea ice covers 15 million square kilometers of the north polar region, an area exceeding one and a half times the area of the U. S. Even at the end of the summer melt season, sea ice still covers 7 million square kilometers. This vast ice cover is an integral component of the climate system, being moved around by winds and waves, restricting heat and other exchanges between the ocean and atmosphere, reflecting most of the solar radiation incident on it, transporting cold, relatively fresh water equatorward, and affecting the overturning of ocean waters underneath, with impacts that can be felt worldwide. Sea ice also is a major factor in the Arctic ecosystem, affecting life forms ranging from minute organisms living within the ice, sometimes to the tune of millions in a single ice floe, to large marine mammals like walruses that rely on sea ice as a platform for resting, foraging, social interaction, and breeding. Since 1978, satellite technology has allowed the monitoring of the vast Arctic sea ice cover on a routine basis. The satellite observations reveal that, overall, the Areal Extent of Arctic sea ice has been decreasing since 1978, at an average rate of 2.7% per decade through the end of 1998. Through 1998, the greatest rates of decrease occurred in the Seas of Okhotsk and Japan and the Kara and Barents Seas, with most other regions of the Arctic also experiencing ice Extent decreases. The two regions experiencing ice Extent increases over this time period were the Bering Sea and the Gulf of St. Lawrence. Furthermore, the satellite data reveal that the sea ice season shortened by over 25 days per decade in the central Sea of Okhotsk and the eastern Barents Sea, and by lesser amounts throughout much of the rest of the Arctic seasonal sea ice region, although not in the Bering Sea or the Gulf of St. Lawrence. Concern has been raised that if the trends toward shortened sea ice seasons and lesser sea ice coverage continue, this could entail major consequences to the polar climate and to the lifestyles (and perhaps even the survivability) of polar bears and other polar species.
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observed hemispheric asymmetry in global sea ice changes
Science, 1997Co-Authors: Donald J Cavalieri, Per Gloersen, Claire L Parkinson, Josefino C Comiso, H J ZwallyAbstract:From November 1978 through December 1996, the Areal Extent of sea ice decreased by 2.9 ± 0.4 percent per decade in the Arctic and increased by 1.3 ± 0.2 percent per decade in the Antarctic. The observed hemispheric asymmetry in these trends is consistent with a modeled response to a carbon dioxide–induced climate warming. The interannual variations, which are 2.3 percent of the annual mean in the Arctic, with a predominant period of about 5 years, and 3.4 percent of the annual mean in the Antarctic, with a predominant period of about 3 years, are uncorrelated.