Snow Depth Retrieval on Arctic Sea Ice From Passive Microwave Radiometers—Improvements and Extensions to Multiyear Ice Using Lower Frequencies

• Published in: Journal of geophysical research. Oceans 2018-10, Vol.123 (10), p.7120-7138
• Main Authors: Rostosky, Philip, Spreen, Gunnar, Farrell, Sinead L., Frost, Torben, Heygster, Georg, Melsheimer, Christian
• Format: Article
• Language: English
• Subjects: Accuracy; Airborne sensing; Algorithms; Arctic climates; Arctic sea ice; Climate; Climate studies; Climate system; Coefficients; Depth; Depth measurement; Depth perception; Evaluation; Extreme weather; Geophysics; Ice cover; Ice environments; Instrument depth measurement; Microwave imagery; Microwave radiometers; Predation; Radiometers; Regression analysis; Retrieval; Satellite observation; Satellites; Sea ice; Snow; Snow accumulation; Snow depth; Solar radiation; Spring; Summer; Survival; Warm air; Weather; Weather conditions
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2018JC014028

Snow on sea ice influences the Arctic energy and heat budgets and is therefore important for Arctic climate studies. Methods to derive snow depth based on satellite‐borne microwave radiometer observations have existed since the 1990s. However, in the Arctic the most widely used algorithm can only be applied over first‐year ice (FYI) and does not make use of the lower frequencies, which are available since 2002. Here we present three improvements to the current passive microwave snow depth retrieval: (a) We derive new coefficients based on a regression analysis using 5 years of Operation IceBridge airborne snow depth measurements. (b) We extend the algorithm to take advantage of the lower frequency channel at 7 GHz. (c) We consider an extension of the snow depth retrieval to multiyear ice (MYI) during spring. Our results show that the gradient ratio, GR(19/7) is most suited for deriving snow over both Arctic FYI (R =°−0.73) and MYI (R = −0.57). An evaluation of the new retrieval with Operation IceBridge snow depth measurements from March and April 2015 shows a good agreement over FYI (difference = −2.1 cm; 93% of the differences below 5 cm). Over MYI the difference is −4.0 cm and 56% of the differences are below 5 cm, that is, the root mean square distance (RMSD) is larger over MYI than over FYI. We demonstrate for the first time that spring snow depth measurements can be derived from passive microwave observations over both FYI and MYI. Plain Language Summary Snow on Arctic sea ice plays an important role in the Arctic climate system. It reflects the majority of the incoming solar radiation and isolates the sea ice from warm air in summer. However, the vast area and the extreme weather conditions make it difficult to monitor changes in snow depth during the Arctic winter. In this study, we develop a retrieval for snow depth on Arctic sea ice based on satellite observations. The advantages of satellite observations are that they provide daily coverage of the whole Arctic. We compare satellite observations in the microwave regime to airborne snow depth measurements, obtained in March and April from 2009 to 2015. We find a good agreement between changes in the signal observed by the satellite and changes in the measured snow depth when the ice is smooth. Over multiyear ice, ice that has survived at least one summer melt and that is often rough, the agreement is not as good. We demonstrate for the first time that spring snow depth estimations for the whole sea