Ground-based evaluation of MODIS snow cover product V6 across China: Implications for the selection of NDSI threshold
Ground-based evaluation of MODIS snow cover product V6 across China: Implications for the selection of NDSI threshold
复制标题
MODIS积雪产品V6全国地基评估：对NDSI阈值选择的启示
DOI：
10.1016/j.scitotenv.2018.10.128
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发表时间：
2019
影响因子：
9.8
通讯作者：
Ma Ning
中科院分区：
文献类型：
--
作者：
Zhang Hongbo;Zhang Fan;Zhang Guoqing;Che Tao;Yan Wei;Ye Ming;Ma Ning
新的中分辨率成像分光仪每日NDSI积雪产品版本6（V6）发布，以取代V5的重大修订。该研究首次基于2003-2013年期间Terra和Aqua的279个和252个站点的每日雪深测量值评估了产品V6在中国的准确性。测试并比较了Terra和Aqua的三种NDSI阈值选择方案：（1）局部最佳NDSI阈值，（2）最小有效NDSI为0.1，（3）全局参考NDSI阈值为0.4。当积雪深度≥ 1 cm时，Terra（Aqua）的最佳、最小和全球参考阈值的平均Cohen's Kappa（CK）分别为0.80（0.60）、0.77（0.58）、0.72（0.51）。NDSI阈值为0.1比0.4更适合于中国的使用。这也得到了晴天积雪日计算精度比较的支持。Terra V6和Terra V5的精度相当，而Aqua V6的精度比Aqua V5更高。在V6中采用的修正温度屏算法被发现在高海拔站中存在较大的雪委托误差。在区域上，产品V6在青藏高原的Terra和Aqua的最佳阈值方面表现出较低的CKs，分别为0.61和0.35，这归因于其高海拔和相对较小的积雪深度。该研究为MODIS积雪产品V6在中国的应用提供了实际意义。
The new MODIS daily NDSI snow cover product version 6 (V6) is released to replace V5 with significant revisions. This study evaluates, for the first time, the accuracy of product V6 across China based on daily snow-depth measurements during 2003–2013 from 279 and 252 stations for Terra and Aqua, respectively. Three schemes of selecting NDSI thresholds for Terra and Aqua were tested and compared including: (1) the locally optimal NDSI threshold, (2) the minimum valid NDSI of 0.1, and (3) the global reference NDSI threshold of 0.4. The mean Cohen's Kappa (CK) of the optimal, minimum and global reference thresholds for Terra (Aqua) are 0.80 (0.60), 0.77 (0.58), 0.72 (0.51), respectively, while snow depth ≥ 1 cm. The NDSI threshold of 0.1 is demonstrated to be more reasonable than the threshold of 0.4 for use in China. This is also supported by the accuracy comparison conducted for the clear-day snow-cover day calculation. Terra V6 and Terra V5 have comparable accuracies whereas Aqua V6 shows better accuracy than Aqua V5 does. The revised temperature screen algorithm employed in V6 is found to be problematic with large snow commission errors in high altitude stations. Regionally, product V6 presents low CKs of 0.61 and 0.35 for the optimal thresholds of Terra and Aqua in the Tibetan Plateau, which are attributed to its high elevation and relatively small snow depth. This study provides practical implications for use of MODIS snow cover production V6 in China.