The Evolution of AVHRR-Derived Water Temperatures over Lakes in the Mackenzie Basin and Hydrometeorological Applications

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Abstract
The temperature evolution of water bodies is determined and compared over the Mackenzie River hydrological basin. The thermal IR observations used to determine the water temperatures were extracted from NOAA's Advanced Very High Resolution Radiometer (AVHRR) satellite data over the period from April 1999 to September 1999. The IR temperatures were calibrated and adjusted to account for the intervening atmosphere. For each day, 1-km-resolution temperature scenes were generated. From the temperature scenes, clear-sky temperature values were extracted for water bodies with areas larger than 100 km2. The temperature cycle over water bodies can be decomposed into a small positive slope from near 0°C until the water temperature reaches 4°C, followed by a quadratic trend that can be easily fitted. The quadratic curve fit parameters give information for cataloging and comparing each water body's seasonal temperature cycle. Data stratification confirms a strong latitudinal influence on the shape of the curves. Compared to Great Slave Lake, the duration of open water for Lake Athabasca is longer and begins about 16 days earlier; for Great Bear Lake, the cycle is shorter and begins about 45 days later. Fitted maximum temperatures are 15.5°C for Lake Athabasca, 13.7°C for Great Slave Lake, and 6.8°C for Great Bear Lake. The AVHRR-derived seasonal temperatures should be useful in estimating total lake evaporation because lakes with longer and warmer seasonal temperature cycles should tend to evaporate over longer time periods than those with shorter and cooler temperature cycles.