Multitemporal snow cover mapping in mountainous terrain for Landsat climate data record development
نویسندگان
چکیده
a r t i c l e i n f o A multitemporal method to map snow cover in mountainous terrain is proposed to guide Landsat climate data record (CDR) development. The Landsat image archive including MSS, TM, and ETM + imagery was used to construct a prototype Landsat snow cover CDR for the interior northwestern United States. Landsat snow cover CDRs are designed to capture snow-covered area (SCA) variability at discrete bimonthly intervals that correspond to ground-based snow telemetry (SNOTEL) snow-water-equivalent (SWE) measurements. The June 1 bimonthly interval was selected for initial CDR development, and was based on peak snowmelt timing for this mountainous region. Fifty-four Landsat images from 1975 to 2011 were pre-processed that included image registration, top-of-the-atmosphere (TOA) reflectance conversion, cloud and shadow masking, and topographic normalization. Snow covered pixels were retrieved using the normalized difference snow index (NDSI) and unsupervised classification, and pixels having greater (less) than 50% snow cover were classified presence (absence). A normalized SCA equation was derived to independently estimate SCA given missing image coverage and cloud-shadow contamination. Relative frequency maps of missing pixels were assembled to assess whether systematic biases were embedded within this Landsat CDR. Our results suggest that it is possible to confidently estimate historical bimonthly SCA from partially cloudy Landsat images. This multitemporal method is intended to guide Landsat CDR development for freshwater-scarce regions of the western US to monitor climate-driven changes in mountain snowpack extent. Continental ice sheets, sea ice, permafrost, and hemispheric-scale seasonal snow cover play an important role in regulating the Earth's radiation balance, and poleward-equatorial latent heat transport during hemispheric cool-seasons (Barry, 2002). Equally important, mountain glaciers and seasonal snow cover (extent) in the form of mountain snowpack (depth) feed seasonal streamflow and replenish hydrological catchments (Barnett et al., 2005; Winther & Hall, 1999). Across the arid western US, mountain ranges serve as seasonal water towers that hold and release snowpack freshwater resources through successive snow accumulation and melt. Snow-fed streamflow contributes approximately 50–70% to the total western US annual water budget (Cayan, 1996). With an automated temporally discrete snow telemetry (SNOTEL) snow-water-equivalent (SWE) measurement network already in place for hydrological forecasting (Serreze et al., 1999), it is quite clear that spatially-explicit, satellite-derived climate data record (CDR) development can augment western US mountain snow-covered area (SCA) monitoring on past, present, and future timescales. Evidence is mounting for alarming declines in western US mountain snowpack as …
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