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A snow cover depletion curve (SDC) summarizes the relationship between snow cover distribution and an average snow cover property, such as depth or water equivalent, for a given area. Snow cover depletion curves have been developed for, and applied in, hydrological models on a watershed or elevation zone basis. However, land cover-based SDCs are not prominent in the literature. For this study the areal distribution of snow cover for dominant land cover units was measured during the winters of 1991 and 1992 in the Laurel Creek watershed in southern Ontario, Canada. On the basis of these data a general model for land cover-based SDCs is developed for these land cover units, namely, short grass, ploughed fields, and deciduous forests. This model is derived from the three-parameter lognormal distribution, which is shown to characterize the areal depletion curves of the land cover units studied. The SDCs based on this new model provide a formal distributed snow cover representation that can be used in vegetation-based distributed hydrological models requiring accurate spatial representations of snow cover attributes. Recent advances in data acquisition can provide detailed hydrological information on a basin-wide scale, thereby increasing our fundamental understanding of the system as a whole.The response to this newly available information has been a change in modeling emphasis from lumped index models to physically based distributed models (e.g., Systame Hydrologique Europ6en (SHE) [Abbot et al., 1986] and WAT-FLOOD [Kouwen, 1988]). Despite the advances in modeling and remote measurement of watershed state and input parameters, simulation of snow cover runoff in low-relief regions using distributed runoff models has yet to be addressed. This is due to the inability to adequately measure and represent the spatial distribution of precipitation and snow cover [MacLaren Plansearch, 1984]. Rain gauges are usually inoperative during winter and early spring, and a distributed representation of the rainfall is difficult to obtain, especially if hourly data are required. The main source of snow cover information is snow course data, which are not generally representative of the watershed terrain and cover [Goodison et al., 1987]. As a result, snowmelt runoff models have not evolved to the point where spatially distributed representation of the important snow cover parameters can be established on a watershed scale. The spatial distribution of the snow cover is described by snow cover depletion curves (SDCs), which summarize the percent areal coverage of the snowpack as it increases in average depth. Watershed-wide SDC relationships are currently used in lumped hydrological models such as the National Weather Service River Forecast System [Anderson, 1973] to describe the snow cover distribution as the snow cover melts. These relationships have not been based on vegetation or terrain classifications and typically require calibration for each specific watershed, making them difficult to obtain. Despite the recognized limitation...

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RESUMEDes images obtenues al'aide d'un radar aantenne syntbetique (RAS) aeroporte dans la bande C, en polarisation HH, et des images RADARSATsimutees d'une partie du bassin de Grand River, en Ontario, ont servi aeualuer l'uttlite des donnees micro-ondes pour la cartograpbie de la couverture de neige mouillee. Deux sites distincts d'une superficie de 5 km 2 ont ete examines. La couverture de neige etait discontinue lors de l'acquisition des images. La surface couverte a ete repartie, aux fins de l'analyse, en trois classes: champ denude, champ recouvert de neige et foret/broussailles. L'exactitude des resultats de classification obtenus avec les images RAS et avec les images RADARSATsimulees a ete eualuee en comparant les images classifiees avec une photographie aerienne representant la couverture de neige discontinue. L'analyse a demontre que l'on pouvait distinguer la signature spectrale des champs denudes de celie des champs recouverts de neige et, ainsi, obtenir d'excellents resultats de classification pour ce qui est de discriminer ces deux classes. En effet, les deux tyes d'images ont permis d'obtenir un taux d'exactitude de 83 pour cent dans le cas des champs recouverts de neige et de 80 pour cent dans le cas des champs denudes. Les resultats des estimations, en pourcentage, de la surface couverte de neige sur les sites a l'etude etaient ires satisfaisants. Ceux-ci montrent que les donnees obtenues par des capteurs actifs dans Ie domaine des micro-ondes se pretent bien ala cartograpbie de la couverture de neige vers lafin du priniemps. Les cartes de couverture de neige peuvent fournir des renseignements utiles pour l'etablissement de modeles d'ecoulement d 'eau de fonte nivale et de modeles de circulation atmospberique. SUMMARY Airborne C-HH and simulated RADARSATsynthetic aperture radar (SAR) imagery ofa portion ofthe Grand River basin, inOntario, were used to evaluate the potential ofactive microwave data for mapping wet snowcover. Two separate sites of approximately 5 krrt-were examined. Thesnowcover was discontinuous at the time of image acquisition, and the surface coverage was groupedfor analysis into barefield, snow-coveredfield, andforestlscrub classes. Theclassification accuracy of the airborne and simulated SAR imagery was evaluated by comparing classified images to aerial photography of the discontinuous snow-cover. Analysis showed that the spectral signature ofthe bare and snow-coveredfields are separable and prouidefor excellent classification ofsnow-covered versus bare fields. Classification accuracies ofsnow-covered versus bare fields of83 percent and 80 percent, respectively, were obtainedfor the airborne SAR and the simulated RADARSAT imagery. Percent snow-covered area estimatesfor the sites were satisfactory. These results indicate that active microwave sensors have the potential to map snowcover in the late spring. Snowcover maps can he useful information for snow-melt runoff models and atmospheric circulation models.].R. Donald is with Conestoga-Rovers