Version 2.0 :
This data set contains standardized, manual, visual ship-based sea-ice observations for the Southern Ocean, Antarctic. These are observations mainly from research ships navigating in sea-ice covered waters. These observations are carried out according to the ASPeCt protocol (http://www.aspect.aq).
The data set includes:
- date and time
- latitude, longitude
- a ship/cruise/expedition identifyer
- total sea-ice concentration
- concentration, ice type, ice thickness, ridged ice fraction, ridge height, surface type, snow depth for thickness category I (the thickest sea ice)
- concentration, ice type, ice thickness, ridged ice fraction, ridge height, surface type, snow depth for ice thickness category II (the 2nd thickest sea ice)
- concentration, ice type, ice thickness, ridged ice fraction, ridge height, surface type, snow depth for ice thickness category III (the 3rd thickest sea ice)
- sea water temperature, air temperature, wind speed, wind direction, visibility, total cloud cover, significant weather, comment
Data are given for each ship cruise in chronological order. For temporally overlapping ship cruises data of the cruise starting first come first.
For times or geographic locations without observations and/or for cases where not all parameters listed above were observed, missing values are included.
Information about the cruise / expedition, translations of the used ASPeCt, ASSIST, or - for the meteorological observations - WMO codes, as well as auxiliary information about the specifics of some of these translations are provided within the attributes of the netCDF files.
[ Derived from parent entry - See data hierarchy tab ]
Kern, Stefan (2020). ESA-CCI_Phase2_Standardized_Manual_Visual_Ship-Based_SeaIceObservations_v02. World Data Center for Climate (WDCC) at DKRZ. https://doi.org/10.26050/WDCC/ESACCIPSMVSBSIOV2
Manual visual ship-based observations are often the only data source for sea-ice information in an otherwise data sparse region.
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Description
Manual visual ship-based observations are often the only data source for sea-ice information in an otherwise data sparse region.
The data offered here have been quality checked and standardized. Standardized means that the observations of different ship cruises are combined such that observations of the same parameter occur in the same column. Missing columns are filled. The values used as missing value vary from parameter to parameter, depending on whether it is a floating point or integer variable and depending on whether the variable can have negative values.
Observations are usually conducted by voluntary observers with varying skills / expertise. This limits the accuracy of the observations.
Of the data included the total sea-ice concentration, given in tenth, can be regarded as the most accurate parameter; its accuracy is 5 to 10%. Accuracy is worst in the inter-mediate sea-ice concentration range from ~30% through ~70%. Partial concentrations of ice types of different thickness are possibly less accurate - especially when fractions of quite similar ice types such as thin first-year ice and medium-thick first-year ice are reported.
Next accurate are observations of sea-ice thickness and snow depth (see below though). Accuracies of the observations of other fractions, such as melt-pond fraction or fraction of ridged ice are ~10%. Ridge height observations are possibly the most difficult to evaluate and have a rather unknown accuracy.
Note that most ships tend to follow easy-to-navigate sea-ice conditions. Because of this sea-ice concentrations might be biased low during summer; the same applies all-year round for sea-ice thickness, snow depth, fraction of ridged ice and possibly also ridge height (see Worby et al., J. Geophys. Res., 113, C06S91, 2008 and Kern et al., The Cryosphere, 13, 3261-3307, DOI:10.5194/tc-13-3261-2019, 2019).
I recommend to consider the quality of this data set as Level 2b (Geophysical Variable - basic quality control).
Completeness report
Temporal completeness:
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Description
Temporal completeness:
The data set contains ship-based observations of the years 2002 through 2019. These observations are carried out along ship trajectories. Observations are only available for the time the ship(s) operated in or near the sea-ice cover. Longer periods outside the sea-ice cover might result in a data gap.
The temporal resolution is supposed to be hourly. However, the temporal resolution varies depending on the cruise. Data gaps occur during night and/or periods with zero visibility.
Observations are chronologically ordered for each cruise separately. They are not chronologically ordered and merged in case that two ships report observations at the same date and time. In this latter case, the data set contains the two overlapping time series separately.
Spatial completeness:
Several factors, as are detailed below, influence the spatial coverage:
i) Observations are carried out only along ship trajectories and only at certain time intervals (usually hourly). Hence data are discontinuous along the ships' track and reflect the ice-conditions of an elliptically shaped area of 2 km width (1 km on each side of the ship) of unknown length; the length depends on the skills of the observer, the ships' speed, and the ice conditions
ii) Limited day light and visibility result in data gaps.