Viewable Snow Covered Area Validation Masks over Rugged and Forested Terrain

These data are maps of viewable snow cover generated from panchromatically sharpened cloud-free WorldView-2 and -3 data within 2 days of a Landsat 8 OLI acquisition or near-nadir MODIS acquisition. The spatial resolution of these validation data ranges from 0.34 m to 0.55 m, depending on the view angle of WorldView. ValKey.csv shows the list of validation dates and the corresponding Landsat 8 OLI and MODIS imagery. Validation images from December to June were selected to account for variability in illumination conditions, snow cover, and snow albedo. The imagery spans diverse locations across California’s Sierra Nevada that represent the heavily forested western slope, higher elevation regions, and drier eastern slopes. The WorldView images range from well illuminated alpine scenes above the tree line in June to heavily shadowed scenes below the tree line in December. The snow-covered WorldView pixels are assumed to be pure endmembers of 100% snow, which are then coarsened to Landsat or MODIS spatial resolutions and provided here as geotiffs. Neither WorldView, Landsat, nor MODIS can see through thick tree canopies, so the data is comprised of snow that an optical sensor identifies. Complete methods used to generate the dataset are available in the companion publication: tbd Binary snow cover maps at the native worldview resolution are unsigned 8 bit integers with fill pixels set to zero, snow pixels set to one, and snow free pixels set to two. Fill Pixels [0] Snow Covered Pixels [1] Snow Free Pixels [2] Fractional snow covered area geotiffs in the projections and at the spatial resolution of Landsat 8 and MODIS products are signed 16-bit integers with a fill value of -32768. The divisor and offset are 1000 & 0 respectively. Fractional snow covered area [0-1000)] (divisor of 1000 and offset of 0 for measurement range of 0-1) Fill Pixels [-32768]本数据集为由经过全色锐化处理的无云WorldView-2与WorldView-3影像生成的可视积雪覆盖图，影像采集时间与Landsat 8 OLI成像时间间隔不超过2天，或与近天底视角的MODIS（中分辨率成像光谱仪，Moderate Resolution Imaging Spectroradiometer）成像时间匹配。该验证数据集的空间分辨率介于0.34米至0.55米之间，具体取值取决于WorldView影像的观测视角。ValKey.csv文件列出了各验证日期及对应的Landsat 8 OLI与MODIS影像信息。选取12月至6月的验证影像，以覆盖光照条件、积雪覆盖情况及积雪反照率的变化范围。影像覆盖加利福尼亚州内华达山脉的多样区域，包括植被茂密的西坡、高海拔区域与较为干旱的东坡。WorldView影像涵盖了6月林线以上光照充足的高山场景，至12月林线以下阴影浓重的场景。本数据集中的WorldView积雪像素被假定为100%积雪的纯端元，随后将其重采样至Landsat或MODIS的空间分辨率，以GeoTIFF格式提供。WorldView、Landsat与MODIS均无法穿透茂密林木冠层，因此本数据集仅包含光学传感器可识别的积雪区域。数据集的完整生成方法可参见配套发表论文：待补充（tbd）。原生WorldView分辨率下的二值积雪覆盖图采用无符号8位整数存储，填充像素值设为0，积雪像素设为1，无积雪像素设为2。各像素含义如下：填充像素[0]、积雪覆盖像素[1]、无积雪像素[2]。与Landsat 8及MODIS产品投影一致、空间分辨率匹配的积雪覆盖面积分数GeoTIFF数据采用有符号16位整数存储，填充值为-32768。其缩放因子与偏移量分别为1000与0，对应积雪覆盖面积分数的测量范围为0~1（实际数值=像素值/1000）。各像素含义如下：积雪覆盖面积分数[0~1000]（缩放因子1000、偏移量0，测量范围0~1）、填充像素[-32768]。