Abstract. The presented database contains time-referenced sea ice draft values from upward looking sonar (ULS) measurements in the Weddell Sea, Antarctica. The sea ice draft data can be used to infer the thickness of the ice. They were collected during the period 1990-2008. In total, the database includes measurements from 13 locations in the Weddell Sea and was generated from more than 3.7 million measurements of sea ice draft. The files contain uncorrected raw drafts, corrected drafts and the basic parameters measured by the ULS. The measurement principle, the data processing procedure and the quality control are described in detail. To account for the unknown speed of sound in the water column above the ULS, two correction methods were applied to the draft data. The first method is based on defining a reference level from the identification of open water leads. The second method uses a model of sound speed in the oceanic mixed layer and is applied to ice draft in austral winter. Both methods are discussed and their accuracy is estimated. Finally, selected results of the processing are presented. The data can be downloaded from
Upward-looking sonar (ULS) data were used to analyze thermodynamic sea ice growth. The study was carried out for an ocean region in the central Weddell Sea, for which data of sea ice thickness variability and of the oceanic heat flux through the ice are rare. In the study area the contribution of sea ice deformation to vertical ice growth is relatively small in some years. This provides the opportunity to simulate thermodynamic sea ice growth considering the influence of a snow cover and of the oceanic heat flux. To this end, a modified version of Stefan's law was used. The resulting ice thickness variations were then compared with the ULS measurements. For the investigated cases, the best consistency between data and model results was obtained assuming a snow layer of less than 5 cm thickness and average oceanic heat fluxes between 6 and 14 W m 22 . It is demonstrated that in conjunction with ice drift data and analytical models for thermal sea ice growth, ULS ice thickness measurements are useful for studying the seasonal cycle of growth and decay and for inferring the magnitude of the average oceanic heat flux under sea ice.
The presented database contains time-referenced sea ice draft values from upward looking sonar (ULS) measurements in the Weddell Sea, Antarctica. The sea ice draft data can be used to infer the thickness of the ice. They were collected during the period 1990-2008. In total, the database includes measurements from 13 locations 5 in the Weddell Sea and was generated from more than 3.7 million measurements of sea ice draft. The files contain uncorrected raw drafts, corrected drafts from two different methods and the basic parameters measured by the ULS. The measurement principle, the data processing procedure and the quality control are described in detail. To account for the unknown speed of sound in the water column above the ULS, 10 two correction methods were applied to the data. The first method is based on defining a reference level from the identification of open water leads. The second method uses a model of sound speed in the oceanic mixed layer and is applied to ice draft in austral winter. Both methods are discussed and their accuracy is estimated. Finally, selected results of the processing are presented. The data can be downloaded under 15 As sea ice is affected by rising atmospheric and oceanic temperatures, it is also a sensitive indicator of global climate change.Variability and trends in southern sea ice extent and concentration have been widely studied, mainly by using data from satellite microwave imagery (e.g., Cavalieri and Parkinson, 2008), ship-based observations (e.g., Worby and Comiso, 2004), and his-5 toric reconstructions from whaling records (e.g., Ackley et al., 2003) or ice cores (e.g., Curran et al., 2003).Contrary to the Arctic, the thickness of Antarctic sea ice has not been surveyed by military nuclear submarines. Satellite altimetry over sea ice still suffers from uncertainties induced by the snow cover on the ice (Zwally et al., 2008). Other methods, like 10 drilling, provide only snapshots of sea ice thickness and are mostly biased towards thin ice, as they are restricted to the accessible regions of the ice cover. The use of moored ULS instruments is yet the only way to obtain information on the long-term development of Antarctic sea ice thickness in remote places of the sea ice cover. The Alfred Wegener Institute (AWI) has been running ULS instruments on 13 positions in 15 the Southern Ocean in different years since 1990. They are deployed in austral summer for measurement periods of two or three years and provide a unique data set of Antarctic sea ice thickness. It is the largest array of ice profiling sonars in the Southern Ocean. Measurement principle 20The sonars are ES-300 series ULS instruments, manufactured by Christian Michelsen Research (CMR) in Norway. They transmit sound pulses of 300 ± 15 kHz towards the sea surface. These signals are reflected either by the underside of the ice or, if no ice is present, by the water/air boundary. The two-way travel time of the signals is measured by the instrument and can be converted into a distance. When measuring reflections 25 ...
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