Asking the pikas politely…
This dataset represents an estimate of the day of year (i.e. , "Julian Day") of the onset of the seasonal snowpack. Specifically these are estimates of the last day of bare ground derived from long-term time-series of Landsat TM, ETM, and OLI imagery starting in 1985. To facilitate computation of snow cover duration, day of year is scaled from January 1st of the following year. This means that negative values represent days before January 1st. For example, a snow onset on November 11th, 2021 (Day of Year 315) would be represented in the 2022 map with a value of -50 (315 - 365). These maps combine monthly ground snow cover fraction maps from the USGS Landsat Collection 2 Level 3 fSCA Statistics (https://doi.org/10.5066/F7VQ31ZQ), with a time-series analysis of a spectral snow index (NDSI) using a heirarchical Bayesian model (Gao et al. 2021). The combination of these two approaches allows reconstruction of detailed annual snow persistence maps from sparse imagery time-series (Landsat data have an 8 to 16-day return interval in the absence of clouds). A comparison of these data to independent in-situ observations from SNOTEL and microclimate sensors show that these products capture about 80% of spatial variation in snowpack onset for recent years (2021-2022), and greater than 80% of temporal variation across the full 1985 - 2024 time-series. This is version 2 of the data product, superseding the previous version (version 1), which provided estimates from 1993 - 2022. Improvements in the Bayesian model and input data filtering allow for incorporation of sparser time-series satellite imagery from 1985-1992, and the dataset has been updated for recent years 2023 and 2024. References: Gao, X., Gray, J. M., & Reich, B. J. (2021). Long-term, medium spatial resolution annual land surface phenology with a Bayesian hierarchical model. Remote Sensing of Environment, 261, 112484. https://doi.org/10.1016/j.rse.2021.112484
Knowledge graph centered on Fall Snowpack Onset Annual Time Series for the Upp with 3 nodes and 3 connections. Top connected: Upper East River Beaver Pond, Multi-model PlanetScope snow cover classification.
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