Abstract
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 × 100 m 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 10. K. 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 4. K. Furthermore, the pattern of snow patches and snow-free areas during snow melt in July causes even greater differences of more than 10. K 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 2. K. 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.
| Original language | English |
|---|---|
| Pages (from-to) | 908-922 |
| Number of pages | 15 |
| Journal | Remote Sensing of Environment |
| Volume | 115 |
| Issue number | 3 |
| DOIs | |
| Publication status | Published - 15 Mar 2011 |
| Externally published | Yes |
Bibliographical note
Funding Information:We are grateful to M. Maturilli for providing us with the data of the BSRN station. We thank M. Schumacher, E. Larmanou, M. Sieber and A. le Tressoler from the AWIPEV base in Ny-Ålesund for the ongoing support of our permafrost research, which contributed greatly to the success of this work. We would like to thank four anonymous reviewers whose comments were very helpful in improving the manuscript. We gratefully acknowledge financial support by the Helmholtz Association through a grant ( VH-NG 203 ) awarded to Julia Boike.
Funding
We are grateful to M. Maturilli for providing us with the data of the BSRN station. We thank M. Schumacher, E. Larmanou, M. Sieber and A. le Tressoler from the AWIPEV base in Ny-Ålesund for the ongoing support of our permafrost research, which contributed greatly to the success of this work. We would like to thank four anonymous reviewers whose comments were very helpful in improving the manuscript. We gratefully acknowledge financial support by the Helmholtz Association through a grant ( VH-NG 203 ) awarded to Julia Boike.
Keywords
- Land surface temperature
- MODIS L2 product
- Permafrost
- Subpixel variability
- Svalbard
- Thermal imaging