Normalized Difference Snow Index (NDSI)
Description
Knowledge on the snow extent, depth, and water content is important for water resource management, planning, and forecasting. Monitoring of the snow extent using satellite imagery is useful for understanding snow depletion and recession rates, evaluating snow extent relative to long term average conditions, and is a useful drought metric. Snow cover area is often estimated using the Normalized Difference Snow Index (NDSI) (Crane and Anderson, 1984; Dozier, 1984). Snow is highly reflective in the visible part of the electromagnetic spectrum and highly absorptive in the near-infrared or short-wave infrared band of the spectrum. Reflectance of clouds is usually high in both the visible and infrared bands, allowing for separation of snow and clouds. NDSI usually ranges from -5 to 1, with ~0.5 to 1 representing snow cover. Time series and anomaly maps of NDSI clearly show changes in snow cover for a region. Positive anomalies indicate increased snow cover, whereas negative anomalies indicate decreased snow cover relative to average conditions.
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