Abstract
Surface temperatures derived from satellite thermal infrared (TIR) data are critical inputs for assessing climate change in polar environments. Sea and ice surface temperature (SST, IST) are commonly determined with split window algorithms that use the brightness temperature from the 11 μm channel (BT11) as the main estimator and the difference between BT11 and the 12 μm channel (BTD11–12) to correct for atmospheric water vapor absorption. An issue with this paradigm in the Arctic maritime environment is the occurrence of high BTD11–12 that is not indicative of atmospheric absorption of BT11 energy. The Composite Arctic Sea Surface Temperature Algorithm (CASSTA) considers three regimes based on BT11 pixel value: seawater, ice, and marginal ice zones. A single channel (BT11) estimator is used for SST and a split window algorithm for IST. Marginal ice zone temperature is determined with a weighted average between the SST and IST. This study replaces the CASSTA split window IST with a single channel (BT11) estimator to reduce errors associated with BTD11–12 in the split window algorithm. The single channel IST returned improved results in the CASSTA dataset with a mean average error for ice and marginal ice zones of 0.142 K and 0.128 K, respectively.
Highlights
The determination of high latitude surface temperatures is an important factor in assessing climate change in polar environments [1,2,3,4,5,6]
The revision of the Composite Arctic Sea Surface Temperature Algorithm (CASSTA) dataset reveals that the temperature difference between in situ data and brightness temperature from the 11 μm channel (BT11) for ice is greater than seawater (Figure 5a)
The data implies that the higher differentials between in situ and BT11 values are associated with ice surfaces, which have a lower average emissivity across the Advanced Very High Resolution Radiometer (AVHRR) BT11 band than seawater and snow (Figure 3)
Summary
The determination of high latitude surface temperatures is an important factor in assessing climate change in polar environments [1,2,3,4,5,6]. This is true in the Arctic where surface air temperatures are increasing more rapidly than the global average [7,8]. Polar orbiting satellites equipped with TIR sensors pass over the polar regions approximately 14 times a day and can provide accurate surface temperatures over large areas.
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