A feasible method for fractional snow cover mapping in boreal zone based on a reflectance model
A feasible method for fractional snow cover mapping in boreal zone based on a reflectance model
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DOI：
10.1016/j.rse.2004.11.013
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发表时间：
2005-03
影响因子：
13.5
通讯作者：
Sari J. Metsämäki;S. Anttila;Huttunen J. Markus;J. Vepsäläinen
中科院分区：
文献类型：
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作者：
Sari J. Metsämäki;S. Anttila;Huttunen J. Markus;J. Vepsäläinen
本文提出了一种适用于北方地区积雪覆盖率制图的方法。该方法（SCAmod）基于半经验模型，其中三个反射率贡献者（湿雪、无雪地面和森林冠层）通过有效冠层透射率和SCA相互关联，构成了目标区域的观测反射率。给定反射率观测值，从模型中求解SCA。反射率贡献者的预定值可以调整到可选的波长区域，这使得SCAmod适用于各种光学传感器。有效森林冠层透射率指定了森林对局部反射率观测的影响;它是使用与实际SCA估计中所采用的类似的地球观测数据进行估计的。由于不需要辅助森林数据，这种方法可以对大面积地区进行业务化的积雪测绘。我们的研究区域覆盖404000平方公里，包括所有流域的芬兰（平均面积为60平方公里）和一些跨界流域共同与俄罗斯，挪威和瑞典。应用SCAmod的NOAA/AVHRR无云数据在融化期间获得的2001-2003年，我们估计了所有5845个盆地的积雪面积分数。对芬兰雪道网络现场SCA的验证表明，SCAmod，SCA的15%（绝对SCA单位）的准确性。根据芬兰气象站网络提供的积雪信息进行验证也取得了良好的结果，例如，94%的无雪和完全积雪的盆地得到了确认。SCAmod提供的SCA估计的统计精度推导的一般公式，补充的结果时，采用AVHRR数据。自2001年以来，芬兰环境研究所（SYKE）的SCAmod对芬兰的积雪融化进行了有效监测。自2003年以来，芬兰国家水文建模和预报系统已采用SCA估计数，这表明预报有了很大改进。
A feasible method for mapping the fraction of Snow Covered Area (SCA) in the boreal zone is presented. The method (SCAmod) is based on a semi-empirical model, where three reflectance contributors (wet snow, snow-free ground and forest canopy), interconnected by an effective canopy transmissivity and SCA, constitute the observed reflectance from the target area. Given the reflectance observation, SCA is solved from the model. The predetermined values for the reflectance contributors can be adjusted to an optional wavelength region, which makes SCAmod adaptable to various optical sensors. The effective forest canopy transmissivity specifies the effect of forests on the local reflectance observation; it is estimated using Earth observation data similar to that employed in the actual SCA estimation. This approach enables operational snow mapping for extensive areas, as auxiliary forest data are not needed. Our study area covers 404000 km2, comprising all drainage basins of Finland (with an average area of 60 km2) and some transboundary drainage basins common with Russia, Norway and Sweden. Applying SCAmod to NOAA/AVHRR cloud-free data acquired during melting periods 2001–2003, we estimated the areal fraction of snow cover for all the 5845 basins. The validation against in situ SCA from the Finnish snow course network indicates that with SCAmod, 15% (absolute SCA-units) accuracy for SCA is gained. Good results were also obtained from the validation against snow cover information provided by the Finnish weather station network, for example, 94% of snow-free and fully snow-covered basins were recognized. A general formula for deriving the statistical accuracy of SCA estimates provided by SCAmod is presented, complemented by the results when the AVHRR data are employed. Snow melting in Finland has been operatively monitored with SCAmod in Finnish Environment Institute (SYKE) since year 2001. The SCA estimates have been assimilated to the Finnish national hydrological modelling and forecasting system since 2003, showing a substantial improvement in forecasts.