Comparison of MODIS-derived land surface temperatures with ground surface and air temperature measurements in continuous permafrost terrain

M. Allard,C. R. Duguay,S. Hachem

doi:10.5194/tc-6-51-2012

Abstract

Abstract. Obtaining high resolution records of surface temperature from satellite sensors is important in the Arctic because meteorological stations are scarce and widely scattered in those vast and remote regions. Surface temperature is the primary climatic factor that governs the existence, spatial distribution and thermal regime of permafrost which is a major component of the terrestrial cryosphere. Land Surface (skin) Temperatures (LST) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor aboard the Terra and Aqua satellite platforms provide spatial estimates of near-surface temperature values. In this study, LST values from MODIS are compared to ground-based near-surface air (Tair) and ground surface temperature (GST) measurements obtained from 2000 to 2008 at herbaceous and shrub tundra sites located in the continuous permafrost zone of Northern Québec, Nunavik, Canada, and of the North Slope of Alaska, USA. LSTs (temperatures at the surface materials-atmosphere interface) are found to be better correlated with Tair (1–3 m above the ground) than with available GST (3–5 cm below the ground surface). As Tair is most often used by the permafrost community, this study focused on this parameter. LSTs are in stronger agreement with Tair during the snow cover season than in the snow free season. Combining Aqua and Terra LST-Day and LST-Nigh acquisitions into a mean daily value provides a large number of LST observations and a better overall agreement with Tair. Comparison between mean daily LSTs and mean daily Tair, for all sites and all seasons pooled together yields a very high correlation (R = 0.97; mean difference (MD) = 1.8 °C; and standard deviation of MD (SD) = 4.0 °C). The large SD can be explained by the influence of surface heterogeneity within the MODIS 1 km2 grid cells, the presence of undetected clouds and the inherent difference between LST and Tair. Retrieved over several years, MODIS LSTs offer a great potential for monitoring surface temperature changes in high-latitude tundra regions and are a promising source of input data for integration into spatially-distributed permafrost models.

Highlights

The 2007 Intergovernmental Panel on Climate Change (IPCC) reports a global temperature increase of 0.74 ◦C over the last 100 yr
When Moderate Resolution Imaging Spectroradiometer (MODIS) observations from both Terra and Aqua became available, starting in 2002, the percentage of cloudless days increased to 20 % on average over the Quebec stations and about 46 % over the stations located in Alaska
Only 33 days of daily Land Surface (skin) Temperatures (LST) values were available during each snow-free season from 2000 to 2008 over Alaska and 22 over Quebec

Summary

Introduction

The 2007 Intergovernmental Panel on Climate Change (IPCC) reports a global temperature increase of 0.74 ◦C over the last 100 yr. Observational records show that average temperature in the Arctic has risen at almost twice the rate as the rest of the world in the past few decades (Zhou et al, 2001; Hinzman et al, 2005; IPCC, 2007). Near-surface air temperature trends in the Arctic have been shown to be greater for inland regions than coastal/ocean regions (Comiso, 2003). There are clear signs that change is ongoing in many environmental variables (Kane, 2005), including permafrost whose temperature increase results in a deepening of the active layer and thermokarst (Romanovsky et al, 2002). S. Hachem et al.: Comparison of MODIS-derived land surface temperatures

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