Smooth empirical Bayes estimation of observation error variances in linear systems

A smooth empirical Bayes estimator was developed for estimating the unknown random scale component of each of a set of observation error variances. It is shown that the estimator possesses a smaller average squared error loss than other estimators for a discrete time linear system

Two-impulse reorientation of asymmetric spacecraft

An investigation conducted to determine minimum maneuver costs for attitude reorientation of spacecraft of all possible inertial distribution over a wide range of maneuver angles by use of a two impulse coning method of reorientation is reported. Maneuver cost, proportional to the product of fuel consumed (total impulse) and time expended during a maneuver is discussed. Assumptions included external impulsive control torques, rigid body spacecraft rest-to-rest maneuvers, and no disturbance torques. Results are presented in terms of average cost and standard deviation for various maneuver ranges. Costs of individual reorientations are calculated with the computer program included

Attitude reorientation of spacecraft by means of impulse coning

Minimum maneuver costs for attitude reorientation of spacecraft of all possible inertial distribution over a wide range of maneuver angles by use of the impulse coning method of reorientation was studied. Maneuver cost is proportional to the product of fuel consumed and time expended during a maneuver. Assumptions included impulsive external control torques, rigid-body spacecraft, rest-to-rest maneuvers, and no disturbance torques. Also, coning maneuvers were constrained to have equal initial and final cone angles. Maneuver costs are presented for general reorientations as well as for spin-axis reorientations where final attitude about the spin axis is arbitrary

Administering Colorado’s Water: A Critique of the Present Approach

41 pages. Contains footnotes

Administering Colorado’s Water: A Critique of the Present Approach

41 pages. Contains footnotes

Hydrology and Water Resources of Saskatchewan

© Centre for Hydrology, 117 Science Place University of Saskatchewan, Saskatoon, Saskatchewan February 2005There is little in the natural environment, economy and society of Saskatchewan that is not intimately tied to and sustained by the flow and storage of water. Nowhere else in Canada does the lack or excess of water cause such widespread concern, nor are there many Canadian environments subject to greater seasonal change in precipitation and surface-water storage. Most major landforms of Saskatchewan were created by the deposition and erosion of sediments and rock by water and ice during the glacial and immediate postglacial periods. Saskatchewan’s contemporary hydrology determines the type and location of natural vegetation, soils, agriculture, communities and commerce. However, the scarcity, seasonality and unpredictability of the province’s water resources have proved critical impediments to the productivity of natural ecosystems and to sustainable settlement and economic activity. The hydrology of Saskatchewan is marked by several distinctive characteristics that govern the behaviour of water as a resource in the province (Gray, 1970): i) The extreme variability of precipitation and runoff results in frequent water shortages and excesses with respect to natural and human storage capacities and demand. ii) The seasonality of water supply is manifest in fall and winter by the storage of water as snow, and lake and ground ice, in early spring by rapid snowmelt resulting in most runoff, and in late spring and early summer by much of the annual rainfall. iii) The aridity and gentle topography result in poorly developed, disconnected and sparse drainage systems, and surface runoff that is both infrequent and spatially restricted. iv) The land cover and soils exert an inordinate control on hydrological processes because of small precipitation inputs and limited energy for evaporation and snowmelt. v) The flows in the major rivers of the southern half of the province are largely derived from the foothills and mountains in Alberta. In dry years, arable agriculture can fail over large parts of the province, whilst in wet years, flooding has caused widespread damage to rural and urban infrastructure. Climate change may increase the incidence of both drought and flooding, with earlier spring thaws and increased interannual and interseasonal variability of temperature and precipitation (Covich et al., 1997; Cutforth et al., 1999, Herrington et al., 1997). Changes to the seasonal timing of precipitation can have very severe effects on agriculture and ecosystems; runoff to water bodies and replenishment of groundwater are primarily supplied by spring snowmelt, growth of cereal grains is related to the quantity of rainfall falling between May and early July, maturing and timely harvesting of crops are dependent upon warm dry weather in mid to late summer, and spring runoff is governed by soil moisture reserves in the preceding fall and snowfall the preceding winter (de Jong and Kachanoski, 1987). Saskatchewan’s water resources are vulnerable, as there is little local runoff to the single greatest water resource of the southern prairies, the South Saskatchewan River, which derives overwhelmingly from the Rocky Mountains. Water supplies in the Alberta portion of the South Saskatchewan River system are approaching full apportionment in dry years and the uncertainty imposed by climate change impacts on runoff generation in the mountains makes managing the river increasing difficult. Local water bodies (streams, sloughs, dugouts) are fed by groundwater or small surface drainages, and little runoff is provided by most land surfaces within the ‘topographic catchment’. The effect of soils and vegetation on Saskatchewan hydrology is profound because of the interaction of snow, evaporation and vegetation. In the southern Prairies, water applied from rain or snowmelt to summer-fallowed fields contributes inordinately to runoff, whereas continuously cropped fields, grasses and trees undergo greater infiltration to soils and hence greater evaporation. In the North, evergreen forest canopy and root structures promote infiltration of rainfall or snowmelt to soils and subsequent evaporation. There is much greater runoff and streamflow in boreal forest drainage basins with large cleared areas. This chapter will discuss the key physical aspects of Saskatchewan’s hydrology and water resources, focussing on its drainage basins and the contribution of runoff to streams and lakes within them, its major rivers and their flows, water supply pipelines and river diversions, prairie hydrology, boreal forest hydrology, groundwater and an assessment of the future. Because of its sub-humid, cold region hydrology and low population, water quality concerns in Saskatchewan are primarily related to algal growth in dugouts, and a few cases of contaminated groundwater or immediate downstream effects from sewage outflows, rather than widespread diffuse-source pollution; this chapter will therefore focus on water quantity rather than quality