MAPPING THE NEAR-SURFACE THERMAL REGIME OF THE CONTINUOUS AND DISCONTINUOUS PERMAFROST ZONES WITH THE MODIS SENSOR

摘要

Near-surface or "skin" temperature data obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA's Terra and Aqua satellite platforms offer a promising means for mapping the near-surface temperature, which is important for investigations of the thermal regime of permafrost. The large swath covered by satellite sensors presents the opportunity to compensate for an otherwise limited number of ground-based (point) station measurements at northern latitudes. This is a significant advantage for studies conducted in Arctic and sub-Arctic areas where measurement stations are geographically scattered and most of the time inaccessible. In this study, MODIS land surface (skin) temperature (LST) data are found to be well correlated with near-surface air temperature measurements (2-3 m above ground) from several ground-based stations in herbaceous and shrub tundra environments, located in the continuous permafrost zone of northern Quebec and Alaska (R{sup}2 > 0.81; 4.41 < RMSE < 6.89; -3.58 < mean bias < 5.92). Due to extensive periods of cloudiness in these high-latitude regions (averaging 265 of cloudy days annually), a procedure was devised to interpolate LST for each MODIS pixel (1 km{sup}2) over a complete annual cycle. From this approach, mean annual and mean monthly near-surface temperatures as well as freezing (Fi), thawing indices (Ti), and the ratio Ti/Fi, which help to delimit the areal extent of permafrost, can be calculated for each pixel and then mapped over large areas. The maps presented in this paper represent averages over the period 2000 to 2005.