MCD43A3积雪地表遥感反照率产品精度分析与评价

Evaluating the Performance of MODIS Albedo Products(MCD43A3)over Seasonal Snow-covered Land Surface

积雪反照率对全球的辐射与能量、水循环和气候变化研究都具有十分重要的作用,准确理解积雪地表反照率的精度和不确定性对于积雪反照率产品的应用、改进具有重要意义。以往对反照率产品的评估主要集中在无雪地表或者永久冰雪地表,但是季节性积雪在全球也有广泛的分布,且具有动态变化的特征。利用位于FLUXNET地面站点具有空间代表性的积雪反照率数据,对积雪地表下新版本的MCD43A3反照率产品进行了精度验证与分析。研究区验证结果表明:相比于非雪地表,积雪覆盖下的MCD43A3反照率产品有着较高的缺失率,最高可达24.95%,在积雪期MCD43A3反照率产品采用备份反演算法的比例也比较高,最高可达78.06%。相比于非雪地表,所有站点下的积雪反照率产品的精度均出现了下降,均方根误差(RMSE)最小为0.1015,最大可达0.2387。在积雪期,MCD43A3反照率产品的精度和地表类型密切相关,其中常绿针叶林的精度最低,RMSE最大为0.2387,biasR最大为88.88%,可以看出产品算法对复杂地表的计算和反演能力略有欠缺。验证中还发现了MCD43A3中使用的核函数模型和备份反演算法在积雪反照率产品生产中的不足之处,发现了产品在降雪、融雪阶段和“积雪的短暂停留”事件中积雪状态的有效识别和反演能力不足。

Snow albedo plays a very important role in the study of global radiation and energy,water cycle and climate change.It is of great significance for the application and improvement of snow albedo products to make clear the accuracy and uncertainty of snow albedo.In the past,the evaluation of albedo products mainly focused on the snow-free surface or the permanent snow-covered surface,but the seasonal snow cover is also widely distributed in the world,and has the characteristics of dynamic change.Therefore,the accuracy of the new ver⁃sion of MCD43 albedo product under the seasonal snow cover is verified and analyzed by using the adequate spa⁃tial representative snow albedo data of FLUXNET ground site.Results in the study area indicate that compared with non-snow surface,the missing rate of MCD43A3 albedo products under snow cover is higher,up to 24.95%,and the proportion of MCD43A3 albedo products using backup inversion algorithm is also higher,up to 78.06%.Compared with the non-snow surface,the accuracy of snow albedo products under all stations de⁃creased,with the minimum the Root Mean Square Errors(RMSE)of 0.1015 and the maximum RMSE of 0.2387.In the snow accumulation period,the accuracy of the MCD43A3 albedo product is closely related to the surface type,among which the accuracy of the evergreen coniferous forest is the lowest,with the maximum RMSE of 0.2387 and the maximum relative bias(biasR)of 88.88%.In addition,the shortcomings of kernel function model and backup inversion algorithm used in MCD43A3 in snow albedo product production are illus⁃trated by examples.It is found that the effective recognition and inversion ability of the product is insufficient in snowfall,snowmelt stage and"short stay of snow"event.