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| Snow water equivalent
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| Definition |
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The water content obtained from melting a defined sample of snow.
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| Rationale |
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Snowmelt is important in the seasonal change of energy flux and in soil moisture and ground water re-charge. Mountain snow packs are a primary water resource in semi-arid areas (such as Central Asia and western North America) and a major economic base for tourism.
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| Users |
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Modellers, climate, hydrology, climate impact analysts, change detection analysts, agriculturists, and energy planners (hydropower).
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| Assessment method |
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Tiers 1-3: field sampling; recording devices;
Tier 5: passive microwave emission (experimental).
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| Units of Measure |
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Liquid water equivalent (mm).
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| Frequency of measurement |
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Daily (satellite derived);
Bi-weekly (snow courses);
Daily.
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| Spatial resolution |
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25 x 25 km;
Snow courses representative of terrain and land cover within the vicinity of the GCOS surface network.
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| Accuracy/precision required |
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± 20 % of absolute (satellite);
± 5 mm up to 100 mm;
± 10 mm for greater than 100 mm.
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| Associated measurements |
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Measurements of vegetation canopy and digital elevation model information (one-time) are needed to improve algorithms.
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| Present status |
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Currently there is no global satellite product being produced. The Canadian AES produces a weekly SWE satellite map for selected Canadian regions. Snow courses and pillow data are routinely collected and used by operational hydrologists.
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| R and D needed |
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- Combine surface (station) measurements and satellite passive microwave and visible band data in an operational product (SSM/I, AMSR, and MODIS). Carry out research on canopy and other effects on passive microwave signatures. Evaluate and improve automatic SWE measurements where manned stations are being replaced.
- Assemble archives of station data from Eurasia and North America (from when records began and with associated metadata);
- Implement SWE products containing optimal combinations of satellite and surface data.
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