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Prevalence of Pure Versus Mixed Snow Cover Pixels across Spatial Resolutions in Alpine Environments

机译：高山环境中不同空间分辨率下纯雪域混合雪覆盖像素的普遍性

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Remote sensing of snow-covered area (SCA) can be binary (indicating the presence/absence of snow cover at each pixel) or fractional (indicating the fraction of each pixel covered by snow). Fractional SCA mapping provides more information than binary SCA, but is more difficult to implement and may not be feasible with all types of remote sensing data. The utility of fractional SCA mapping relative to binary SCA mapping varies with the intended application as well as by spatial resolution, temporal resolution and period of interest, and climate. We quantified the frequency of occurrence of partially snow-covered (mixed) pixels at spatial resolutions between 1 m and 500 m over five dates at two study areas in the western U.S., using 0.5 m binary SCA maps derived from high spatial resolution imagery aggregated to fractional SCA at coarser spatial resolutions. In addition, we used in situ monitoring to estimate the frequency of partially snow-covered conditions for the period September 2013–August 2014 at 10 60-m grid cell footprints at two study areas with continental snow climates. Results from the image analysis indicate that at 40 m, slightly above the nominal spatial resolution of Landsat, mixed pixels accounted for 25%–93% of total pixels, while at 500 m, the nominal spatial resolution of MODIS bands used for snow cover mapping, mixed pixels accounted for 67%–100% of total pixels. Mixed pixels occurred more commonly at the continental snow climate site than at the maritime snow climate site. The in situ data indicate that some snow cover was present between 186 and 303 days, and partial snow cover conditions occurred on 10%–98% of days with snow cover. Four sites remained partially snow-free throughout most of the winter and spring, while six sites were entirely snow covered throughout most or all of the winter and spring. Within 60 m grid cells, the late spring/summer transition from snow-covered to snow-free conditions lasted 17–56 days and averaged 37 days. Our results suggest that mixed snow-covered snow-free pixels are common at the spatial resolutions imaged by both the Landsat and MODIS sensors. This highlights the additional information available from fractional SCA products and suggests fractional SCA can provide a major advantage for hydrological and climatological monitoring and modeling, particularly when accurate representation of the spatial distribution of snow cover is critical.
机译：积雪区域（SCA）的遥感可以是二进制的（指示每个像素上是否存在积雪）或分数的（指示每个像素被雪覆盖的比例）。与二进制SCA相比，分数SCA映射提供的信息更多，但更难以实现，并且对于所有类型的遥感数据而言可能都不可行。相对于二进制SCA映射，分数SCA映射的用途随目标应用以及空间分辨率，时间分辨率和关注时间段以及气候而变化。我们使用源自高空间分辨率影像的0.5 m二进制SCA映射，量化了美国西部两个研究区域在五个日期内空间分辨率介于1 m至500 m之间的部分被雪覆盖（混合）像素的出现频率较粗的空间分辨率下的分数SCA。此外，我们使用原位监测来估计2013年9月至2014年8月这段时期内两个有大陆性降雪气候的研究区域的10个60 m网格单元足迹的部分被雪覆盖的频率。图像分析的结果表明，在40 m处（略高于Landsat的名义空间分辨率），混合像素占总像素的25％–93％，而在500 m处，用于积雪制图的MODIS波段的名义空间分辨率，混合像素占像素总数的67％–100％。在大陆性降雪气候点比在海上降雪气候点更常见混合像素。原位数据表明，在186至303天之间存在一些积雪，部分积雪情况发生在有积雪的日子的10％–98％。在整个冬季和春季的大部分时间里，有四个站点保持部分无雪，而在整个冬季和春季的大部分或全部时间内，有六个站点完全被雪覆盖。在60 m的网格单元内，春/夏末从积雪到无雪的过渡持续了17-56天，平均37天。我们的结果表明，在Landsat和MODIS传感器成像的空间分辨率下，混合的积雪覆盖的无雪像素很常见。这突出显示了可从分数SCA产品获得的其他信息，并表明分数SCA可为水文和气候监测与建模提供主要优势，尤其是在精确表示积雪的空间分布至关重要时。

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