Comparison of summer Arctic sea ice surface temperatures from in situ and MODIS measurements
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Comparison of summer Arctic sea ice surface temperatures from in situ and MODIS measurements Na Li1, 2*, Bingrui Li1, 2, Ruibo Lei1, 2, Qun Li1, 2 1 Polar Research Institute of China, Shanghai 200136, China 2 MNR Key Laboratory for Polar Science, Polar Research Institute of China, Shanghai 200136, China
Received 26 October 2019; accepted 18 November 2019 © Chinese Society for Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract
Ship-borne infrared radiometric measurements conducted during the Chinese National Arctic Research Expedition (CHINARE) in 2008, 2010, 2012, 2014, 2016 and 2017 were used for in situ validation studies of the Moderate Resolution Imaging Spectroradiometer (MODIS) sea ice surface temperature (IST) product. Observations of sea ice were made using a KT19.85 radiometer mounted on the Chinese icebreaker Xuelong between July and September over six years. The MODIS-derived ISTs from the satellites, Terra and Aqua, both show close correspondence with ISTs derived from radiometer spot measurements averaged over areas of 4 km× 4 km, spanning the temperature range of 262–280 K with a ±1.7 K (Aqua) and ±1.6 K (Terra) variation. The consistency of the results over each year indicates that MODIS provides a suitable platform for remotely deriving surface temperature data when the sky is clear. Investigation into factors that cause the MODIS IST bias (defined as the difference between MODIS and KT19.85 ISTs) shows that large positive bias is caused by increased coverage of leads and melt ponds, while large negative bias mostly arises from undetected clouds. Thin vapor fog forming over Arctic sea ice may explain the cold bias when cloud cover is below 20%. Key words: sea ice surface temperature, thermal radiometer, MODIS, Arctic Ocean Citation: Li Na, Li Bingrui, Lei Ruibo, Li Qun. 2020. Comparison of summer Arctic sea ice surface temperatures from in situ and MODIS measurements. Acta Oceanologica Sinica, 39(9): 18–24, doi: 10.1007/s13131-020-1644-7
1 Introduction Recently, much attention has been paid to the rapid decline of Arctic sea ice. Observations show a fundamental shift in the character of the Arctic sea ice cover from multiyear ice to seasonal ice, a constant shrink of ice thickness and a lengthening of the summer melt season (Comiso, 2012; Laxon et al., 2013; Markus et al., 2009). Ice surface temperature (IST), which is a crucial variable of the Arctic climate, can indicate the presence of surface melt on summer sea ice and can be considered as an integrator of surface energy fluxes. Accurate and consistent measurements of IST are needed to improve the estimation of the surface heat fluxes and our understanding and ability to predict the effects of climate change in the Arctic. Because of the logistical obstacles in establishing a suitably dense observing network for in situ IST measurements in the Arctic, satellite sensors have been an important source of basin-wide information with their extensive and continual coverage. IST can be mapped globally using the infr
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