Spatial and temporal variations of summer surface temperatures of high-arctic tundra on Svalbard — Implications for MODIS LST based permafrost monitoring
Spatial and temporal variations of summer surface temperatures of high-arctic tundra on Svalbard — Implications for MODIS LST based permafrost monitoring
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DOI：
10.1016/j.rse.2010.11.018
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发表时间：
2011-03
影响因子：
13.5
通讯作者：
S. Westermann;M. Langer;J. Boike
中科院分区：
文献类型：
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作者：
S. Westermann;M. Langer;J. Boike
地表温度是决定北极地区多年冻土热状况的关键参数之一。由于多年冻土区地处偏远，利用遥感技术对地表温度进行监测是十分必要的。然而，合适的卫星平台，如中分辨率成像光谱仪提供的空间分辨率，不能解决相当小规模的表面条件的异质性的特点，许多永久冻土区。本研究探讨了挪威斯瓦尔巴特群岛高北极苔原夏季地表温度的空间变异。安装在桅杆上的热成像系统有助于连续监测大约100× 100米的苔原，从雪融化到秋天的整个夏季，不同的表面覆盖和土壤湿度条件变化很大。净辐射被认为是一个控制参数的差异，在表面温度之间的潮湿和干燥的地区。在7月晴朗的天气条件下，干湿地区的地表温度差异可达10K。地表温度周平均值的空间差异显著减小，这与深层土壤温度的演变有关。尽管如此，仍然存在相当大的变化，潮湿和干燥地区之间的最大差异为3至4K。此外，在7月融雪期间，雪斑和无雪区的模式导致每周平均值的差异甚至超过10K。在夏季结束时，地表温度的差异逐渐减小。由于在7月的显着的空间变异性，累计无雪期的度日总数可以在整个研究区域的差异超过60%。从热成像系统的地面观测进行比较，从中分辨率成像光谱仪传感器的陆地表面温度的测量。在经常晴朗的天空条件，从而高密度的卫星数据期间，每周平均计算热成像系统和中分辨率成像分光光度计LST同意在小于2K。当长时间的多云天气妨碍卫星测量时，会出现较大的偏差。此外，所采用的MODIS L2 LST数据集包含了一些强偏置的测量，这表明云顶温度的混合。我们的结论是，一个可靠的间隙填充程序，以减轻长期多云的影响，将是未来的LST为基础的冻土监测计划的高价值。夏季地表温度的持续子像素变化的发生是一个复杂的因素，其影响需要进一步评估结合其他空间可变参数，如积雪和土壤特性。
The ground surface temperature is one of the key parameters that determine the thermal regime of permafrost soils in arctic regions. Due to remoteness of most permafrost areas, monitoring of the land surface temperature (LST) through remote sensing is desirable. However, suitable satellite platforms such as MODIS provide spatial resolutions that cannot resolve the considerable small-scale heterogeneity of the surface conditions characteristic for many permafrost areas. This study investigates the spatial variability of summer surface temperatures of high-arctic tundra on Svalbard, Norway. A thermal imaging system mounted on a mast facilitates continuous monitoring of approximately 100×100m of tundra with a wide variability of different surface covers and soil moisture conditions over the entire summer season from the snow melt until fall. The net radiation is found to be a control parameter for the differences in surface temperature between wet and dry areas. Under clear-sky conditions in July, the differences in surface temperature between wet and dry areas reach up to 10K. The spatial differences reduce strongly in weekly averages of the surface temperature, which are relevant for the soil temperature evolution of deeper layers. Nevertheless, a considerable variability remains, with maximum differences between wet and dry areas of 3 to 4K. Furthermore, the pattern of snow patches and snow-free areas during snow melt in July causes even greater differences of more than 10K in the weekly averages. Towards the end of the summer season, the differences in surface temperature gradually diminish. Due to the pronounced spatial variability in July, the accumulated degree-day totals of the snow-free period can differ by more than 60% throughout the study area. The terrestrial observations from the thermal imaging system are compared to measurements of the land surface temperature from the MODIS sensor. During periods with frequent clear-sky conditions and thus a high density of satellite data, weekly averages calculated from the thermal imaging system and from MODIS LST agree within less than 2K. Larger deviations occur when prolonged cloudy periods prevent satellite measurements. Furthermore, the employed MODIS L2 LST data set contains a number of strongly biased measurements, which suggest an admixing of cloud top temperatures. We conclude that a reliable gap filling procedure to moderate the impact of prolonged cloudy periods would be of high value for a future LST-based permafrost monitoring scheme. The occurrence of sustained subpixel variability of the summer surface temperature is a complicating factor, whose impact needs to be assessed further in conjunction with other spatially variable parameters such as the snow cover and soil properties.