Generating accurate skin sea surface temperature data from observations made using multiple platforms during CASPER field experiment
Alappattu, Denny P.
Lind, Richard J.
Christman, Adam J.
Fernando, Harindra Joe
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The east coast field campaign of Coupled Air-Sea Processes and Electromagnetic ducting Research (CASPER) was conducted in the fall of 2015 offshore of Duck, North Carolina. CASPER observations were conceived to better our understanding of the role of coupled air-sea processes on marine atmospheric surface layer (MASL) thermodynamics and its implications on radio frequency (RF) propagation. MASL measurements during CASPER were chiefly made from research vessels and research aircraft. Continuous and synchronized observations in the study region were made from the R/V Hugh R. Sharp (hereafter Sharp) and the R/V Atlantic Explorer (hereafter Explorer). Two research aircraft, CIRPAS Twin Otter (TO) with a controlled towed vehicle (CTV) and the SAAB 340 aircraft from the Naval Research Laboratory, were also utilized to collect measurements. A fundamental and important measurement required for air-sea interaction and RF propagation research is the sea surface temperature (SST). In this context, this report consolidates the efforts taken to ensure the accuracy of SST observation made from research vessels and aircraft. During the experiment conventional bulk SST measurements using thermistors were taken from the Sharp and Explorer from ~1 m and ~2 m below the water line, respectively. In addition to these, an Infrared SST Autonomous Radiometer (ISAR) was deployed on the Sharp to measure the skin sea surface temperature (skin SST). However, skin SST data loss occurred in the ISAR observations due to frequent rain and sea-spray conditions when the instrument halts sampling to protect the optics. Bulk SST can differ from skin SST up to O(1°C) due to the cool skin and/or warm layer effects caused by the absorption of insolation, heat exchange with the atmosphere, and subsurface turbulent mixing. Skin SST is the water temperature relevant in studies related to air-sea interaction and needs to be used in MASL applications instead of bulk SST. In the absence of skin SST, it is appropriate to use bulk SST adjusted for cool skin and warm layer effects. Accurate representations of skin temperature from the Sharp and Explorer bulk SST datasets are required for further CASPER interdisciplinary research. Two different procedures were used to create corrected SST datasets from Sharp and Explorer observations. Bulk-skin SST difference and the factors governing its variability were used to correct the Sharp bulk SST for cool skin and warm layer effects. This corrected bulk SST is used to fill data gaps in the skin SST and create a corrected composite SST dataset for Sharp. The relationship between Explorer bulk SST and the Sharp corrected composite SST when the ships were within 5 km of each other was used to adjust Explorer bulk SST observations and make them equivalent to Sharp corrected composite SST.
NPS Report NumberNPS-MR-17-001
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