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  • 2000-2004  (5)
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  • 1
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    Ice-cover variability on shallow lakes at high latitudes: model simulations and observations (2003)
    Wiley
    Details
    Publication Date: 2003-01-01
    Description: A one-dimensional thermodynamic model for simulating lake-ice phenology is presented and evaluated. The model can be driven with observed daily or hourly atmospheric forcing of air temperature, relative humidity, wind speed, cloud amount and snowfall. In addition to computing the energy balance components, key model output includes the temperature profile at an arbitrary number of levels within the ice/snow (or the water temperature if there is no ice) and ice thickness (clear ice and snow-ice) on a daily basis, as well as freeze-up and break-up dates. The lake-ice model is used to simulate ice-growth processes on shallow lakes in arctic, sub-arctic, and high-boreal forest environments. Model output is compared with field and remote sensing observations gathered over several ice seasons. Simulated ice thickness, including snow-ice formation, compares favourably with field measurements. Ice-on and ice-off dates are also well simulated when compared with field and satellite observations, with a mean absolute difference of 2 days. Model simulations and observations illustrate the key role that snow cover plays on the seasonal evolution of ice thickness and the timing of spring break-up. It is also shown that lake morphometry, depth in particular, is a determinant of ice-off dates for shallow lakes at high latitudes. © 2003 John Wiley and Sons, Ltd.
    Print ISSN: 0885-6087
    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley
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  • 2
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    RADARSAT backscatter characteristics of ice growing on shallow sub-Arctic lakes, Churchill, Manitoba, Canada (2002)
    Wiley
    Details
    Publication Date: 2002-01-01
    Description: Results from an investigation on the evaluation of RADARSAT (C-HH) imagery for monitoring ice growth and decay, and related processes of shallow sub-Arctic (tundra and forest) lakes in northern Manitoba, Canada, are presented. Field observations on the structural and stratigraphic characteristics of snow and ice from four lake sites are used in support of the interpretation of changes in synthetic aperture radar backscatter intensity as a function of time and incidence angle (20-49°). Results show that bubble inclusions, most of which are tubular and oriented in the direction of growth, strongly influence backscatter intensity from floating ice in RADARSAT Standard beam mode imagery. It is shown that radar return can vary considerably as a function of incidence angle. Differences of as much as 6.5 dB were observed for the same ice cover when observed at steeper (20-35°) compared with shallower (35-49°) incidence angles. During the early stages of ice growth and/or when the ice volume contains a small amount of tubular bubbles, backscatter intensity from the floating ice measured at shallower incidence angles (35-49°) is similar to that observed from the grounded ice at any incidence angle (-17 to -11 dB). A strong decrease in backscatter was observed at all sites during spring thaw and was explained by the microwave signal being absorbed by the wet snow cover and by specular reflection from the standing water (ponds) on the lake ice surface. With its multiple beam mode configurations, RADARSAT offers an improved temporal coverage over ERS-1/2, thus making it possible to determine more precisely freeze-up and break-up dates, and timing of bottom freezing from shallow Arctic and sub-Arctic lakes. Copyright © 2002 John Wiley & Sons, Ltd.
    Print ISSN: 0885-6087
    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley
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  • 3
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    Development of a historical ice database for the study of climate change in Canada (2002)
    Wiley
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    Publication Date: 2002-01-01
    Description: The Canadian government has been compiling various observations on freshwater and coastal sea ice conditions for many years. However, the records are not easily accessible and are dispersed within different government departments. Given this, a major effort was undertaken in order to gather all available observations into a common database-the Canadian Ice Database (CID). This database will respond to the needs for climate monitoring in Canada, the validation and improvement of numerical ice models and the development of new remote-sensing methods. Indeed, several studies have shown that freshwater ice and sea ice are good proxy indicators of climate variability and change. The first version of CID contains in situ observations from 757 sites distributed across Canada, which were originally kept on digital or paper records at the Meteorological Service of Canada Headquarters and the Canadian Ice Service (CIS). The CID holds 63 546 records covering the period from ice season 1822-23 to 2000-01. An analysis of the database allows one to trace the temporal evolution of the ice networks. The freeze-up/break-up network of 2000-01 only represents 4% of what it was in 1985-86. A drastic decline of the ice thickness and the snow on ice network is also observable. In 1997-98, it represented only 10% of the network that existed in 1984-85. The major budget cuts in Canadian government agencies during the late 1980s and the 1990s offer the most plausible explanation for the drastic decline in the ice observation networks. Weekly ice coverage determination on large lakes from satellite imagery by the CIS and the national volunteer ice monitoring program, Ice Watch, may provide a means of reviving, at least, the freeze-up/break-up network. Copyright © 2002 John Wiley and Sons, Ltd.
    Print ISSN: 0885-6087
    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley
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  • 4
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    Simulation of ice phenology on Great Slave Lake, Northwest Territories, Canada (2002)
    Wiley
    Details
    Publication Date: 2002-12-11
    Description: A one-dimensional thermodynamic lake ice model (Canadian Lake Ice Model or CLIMo) is used to simulate ice phenology on Great Slave Lake (GSL) in the Mackenzie River basin, Northwest Territories, Canada. Model simulations are validated against freeze-up and break-up dates, as well as ice thickness and on-ice snow depth measurements made in situ at three sites on GSL (Back Bay near Yellowknife, 1960-91; Hay River, 1965-91; Charlton Bay near Fort Reliance, 1977-90). Freeze-up and break-up dates from the lake ice model are also compared with those derived from SSM/I 85 GHz passive microwave imagery over the entire lake surface (1988-99). Results show a very good agreement between observed and simulated ice thickness and freeze-up/break-up dates over the 30-40 years of observations, particularly for the Back Bay and Hay River sites. CLIMo simulates the ice thickness and annual freeze-up/break-dates with a mean error of 7 cm and 4 days respectively. However, some limitations have been identified regarding the rather simplistic approach used to characterize the temporal evolution of snow cover on ice. Future model improvements will therefore focus on this particular aspect, through linkage or coupling to a snow model. Copyright © 2002 John Wiley and Sons, Ltd.
    Print ISSN: 0885-6087
    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley
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  • 5
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    Use of passive-microwave data to monitor spatial and temporal variations of snow cover at tree line near Churchill, Manitoba, Canada (2002)
    Cambridge University Press
    Details
    Publication Date: 2002-01-01
    Description: We evaluated the contribution of Special Sensor Microwave/Imager (SSM/I) passive-microwave data to the monitoring of spatial and temporal variability of snow cover in the Churchill area, Manitoba, Canada. Because of the coarse spatial resolution of current passive-microwave sensors, the estimation of snow water equivalent using empirical equations with these instruments is largely compromised in complex areas such as Churchill (forest–tundra ecotone). However, with its high frequency of observations and the availability of a long time series (1988–99), passive-microwave data from the SSM/I radiometer remain a very valuable tool for monitoring the temporal evolution of snow cover at various spatial scales. Through winter 1997/98, we first examined the passive-microwave signatures at the local scale and we identified the major stages of the snow period. Principal-component analysis (PCA) applied on spectral-difference (Tb(19H) - Tb(37H))time series (1988–99) enabled us to identify spatio-temporal effects over a large area. PCA also permitted the extraction of indices of relevance for monitoring climatic variability and climate change (annual snow-cover duration, dates of snow-cover appearance and disappearance).
    Print ISSN: 0260-3055
    Electronic ISSN: 1727-5644
    Topics: Geography , Geosciences
    Published by Cambridge University Press on behalf of International Glaciological Society.
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