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This data set consists of moored Upward Looking Sonar (ULS) data from 14 stations in the Weddell Sea. Parameters in the processed data files are water pressure, water temperature, draft, and a flag to indicate if the instrument is under ice. Raw data files contain additional parameters. These data were contributed by the Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany, in 1999. Data are available via FTP.
Please acknowledge use of these data. Citations in reference lists accompanying published work should be stated as follows:
Harms, S., E. Fahrbach, and V.H. Strass. 2001. AWI moored ULS data, Weddell Sea (1990-1998). Boulder, CO: National Snow and Ice Data Center. http://dx.doi.org/10.7265/N58G8HM9
Please send the citation for any publication that uses this data set to NSIDC User Services.
Formerly with Alfred Wegener Institute for Polar and Marine Research
Am Handelshafen 12
D-27570 Bremerhaven, Germany
These data from moored Upward Looking Sonar (ULS) were contributed to NSIDC by the Alfred Wegener Institute for Polar and Marine Research in 1999. Dr. Sabine Harms provided material for this documentation in addition to the data. See the cited references for more information on the instruments used to collect these data and the research program that allowed these data to be produced.
Measurements have a sample interval of between 3 and 15 minutes. Data record length for individual stations ranges from under a year to about two years.
|ANT XIII/4||206-4||9||ES-300 V||3.00||S63°29.6'||W52°06.1'||960||157||15||May 8, 1996||Jan. 8, 1998|
|ANT IX/2||207-2||6||ES-300 V||1.00||S63°45.1'||W50°54.3'||2461||125||8||Nov. 22, 1990||Nov. 26, 1992|
|ANT XIII/4||207-4||8||ES-300 V||3.00||S63°43.3'||W50°49.2'||2510||174||15||April 27, 1996||Nov. 7, 1997|
|ANT X/7||208-3||24||ES-300 V||1.00||S65°37.7'||W36°29.4'||4766||150||8||Jan. 4, 1993||July 25, 1994|
|ANT X/7||209-3||25||ES-300 V||1.00||S66°37.4'||W27°07.2'||4860||132||8||Dec. 31, 1992||Nov. 10, 1993|
|ANT IX/2||210-2||7||ES-300 V||1.00||S69°39.6'||W15°42.9'||4750||125||8||Dec. 11, 1990||Dec. 16, 1992|
|ANT IX/2||212-2||9||ES-300 V||1.00||S70°54.7'||W11°57.8'||1550||125||8||Dec. 14, 1990||Dec. 18, 1992|
|ANT IX/2||217-1||10||ES-300 V||1.00||S64°25.1'||W45°51.0'||4390||125||8||Nov. 24, 1990||Nov. 26,1992|
|ANT X/7||227-3||10||ES-300 V||1.00||S59°01.8'||E 00°00.0'||4605||156||8||April 4, 1996||Jan. 10, 1997|
|ANT XIII/4||227-4||37||ES-300 VI||4.00||S59°01.8'||W00°OO.9'||4600||145||3||Jan. 9, 1997||April 11, 1998|
|ANT XIII/4||229-1||7||ES-300 V||3.00||S64°00.0'||W00°OO.0'||5186||165||15||April 18, 1996||Dec. 24, 1997|
|ANT XIII/4||231-1||26||ES-300 V||3.00||S67°00.0'||W00°00.4'||4510||160||15||April 12, 1996||Dec. 27, 1997|
|ANT XIII/4||232-1||24||ES-300 V||3.00||S69°00.0'||E 00°00.0'||3361||147||15||April 21, 1996||Feb. 16, 1997|
|ANT XIII/4||233-2||34||ES-300 VI||4.00||S69°24.0'||E 00°00.0'||1960||154||3||Feb. 16, 1997||March 12, 1998|
In version 1.0, four travel times are measured, but only the two most similar travel times are stored, and only one signal strength is stored. In higher versions, four travel times are measured and all four travel times are stored, and for each travel time the signal strength is stored.
Data and information are stored in the following files:
The following sample is taken from the file uls206_4.end . "NaN" indicates bad or no data.
ULS206-4 Processed Data (See ULS206_README.TXT for information) -63 -29.6 -52 -6.1 96 5 8 14 7 12 00 900.0 960 157 REC PRES TEMP DRAFT FLAG AWI206-4 ULS206-4 (SN 09) # 1 NaN -2.09 NaN NaN 2 NaN -2.09 NaN NaN 3 NaN -2.09 NaN NaN 4 NaN -2.09 NaN NaN 5 NaN -2.09 NaN NaN 6 NaN -2.09 NaN NaN 7 NaN -2.09 NaN NaN 8 NaN -2.09 NaN NaN 9 NaN -2.09 NaN NaN 10 NaN -2.09 NaN NaN 11 NaN -2.09 NaN NaN 12 NaN -2.09 NaN NaN 13 NaN -2.09 NaN NaN 14 NaN -2.09 NaN NaN 15 NaN -2.09 NaN NaN 16 NaN -2.09 NaN NaN 17 NaN -2.09 NaN NaN 18 NaN -2.09 NaN NaN 19 NaN -2.09 NaN NaN 20 NaN -2.09 NaN NaN 21 NaN -2.09 NaN NaN 22 NaN -2.09 NaN NaN 23 NaN -2.09 NaN NaN 24 130.99 -1.05 0.22 1 25 130.99 -1.04 0.06 0 26 130.99 -1.03 0.14 1 27 130.99 -1.01 0.15 1 28 130.99 -1.00 -0.02 0 29 130.99 -0.99 2.26 1 30 130.99 -0.98 0.34 0 31 130.99 -0.97 1.33 1 32 130.99 -0.95 2.01 1 33 130.99 -0.94 NaN NaN 34 130.99 -0.92 0.65 1 35 130.99 -0.90 -0.30 0
The format is as follows:
0 = water
1 = ice <= 20M
2 = ice > 20m
NaN = bad or no data
NOTE: ice drafts greater than 20 m may be outliers that were not associated with obvious outliers in the raw data (that is, outliers in pressure, temperature, tilt, signal strength, etc.)
The following sample is from the file uls206_4.raw. "NaN" indicates bad or no data.
ULS206-4 Raw Data (See ULS206_README.TXT for information) -63 -29.6 -52 -6.1 96 5 8 14 7 12 00 900.0 960 157 REC PRES TEMP TILT VENV1 VENV2 VENV3 VENV4 TIME1 TIME2 TIME3 TIME4 ATMP SPEEDSP DRAFT1 DRAFT2 DRAFT3 DRAFT4 ERR AWI206-4 ULS206-4 (SN 09) # 1 NaN -2.09 0.0 15.00 15.00 15.00 15.00 393216 393216 393216 393216 0.00 NaN NaN NaN NaN NaN 2 2 NaN -2.09 0.0 16.00 15.00 16.00 16.00 393216 393216 393216 393216 0.00 NaN NaN NaN NaN NaN 2 3 NaN -2.09 0.0 16.00 15.00 16.00 15.00 393216 393216 393216 393216 0.00 NaN NaN NaN NaN NaN 2 4 NaN -2.09 0.0 16.00 15.00 16.00 16.00 393216 393216 393216 393216 0.00 NaN NaN NaN NaN NaN 2 5 NaN -2.09 0.0 15.00 16.00 15.00 16.00 393216 393216 393216 393216 0.00 NaN NaN NaN NaN NaN 2 6 NaN -2.09 0.0 15.00 16.00 15.00 16.00 393216 393216 393216 393216 0.00 NaN NaN NaN NaN NaN 2 7 NaN -2.09 0.0 16.00 16.00 15.00 15.00 393216 393216 393216 393216 0.00 NaN NaN NaN NaN NaN 2
The format is as follows:
The image below is an example of the file for processed data from mooring 206-4.
Information for this section of the documentation was obtained from Strass (1998). See Strass (1998) for detailed information on data processing.
Moored upward looking sonars measure sea ice draft by transmitting pulses of sound toward the surface, and measuring the time elapsed until the echo of a pulse is received back at the instrument. Time is converted to distance using assumptions about the profile of sound speed in the water between the instrument and the surface. If the depth of the instrument is known, and the location of the open water surface is apparent in the echo record, the depth (or draft) of the under-ice surface can be calculated.
Processing raw upward looking sonar data to produce draft measurements involves accounting for factors that introduce errors. For example, sound velocity depends on water density, which in turn depends on temperature and salinity. These parameters vary seasonally and on shorter time scales. The depth of the instrument is measured by a pressure sensor, and this measurement must be corrected for variations in pressure caused by variations in water density and air pressure. These factors and others are accounted for in the following processing steps:
Temperature profiles are determined for each mooring location individually using profiles measured at the mooring positions during deployment and recovery. These are adjusted over time with temperature measured continuously at the ULS. The salinity distribution is approximated using salinity profiles measured during deployment and recovery, adjusted over time using an assumed linear relationship between temperature and salinity. Approximated seasonal cycles of temperature and salinity are combined with the vertical temperature and salinity distributions. Density and sound velocity are then calculated from standard oceanographic formula using the vertically and temporally varying temperature and salinity profiles.
Continuous time series of air pressure at the mooring locations are produced by interpolating values from European Centre for Medium Range Weather Forecasting six hour air pressure fields. Variations in air pressure are then removed from the ULS pressure readings before instrument depth is calculated.
Data are rejected if (a) the measured temperature or pressure is out of range (b) the strength of the echo falls below a threshold or the tilt of the instrument exceeds five degrees (c) the difference between the two most similar draft measurements obtained from a single pulse exceeds 2 m, or (d) the draft is larger than the ULS depth or less than -10 m.
At this stage in data processing a draft of zero does not necessarily correspond to the water surface because the sound velocity model is not accurate enough for discrimination between thin ice and open water, and because waves distend the water surface. An initial discrimination between ice and open water is based on a measure of echo strength (larger for echoes from open water) and a measure of short term draft variability (higher for open water), as well as on draft.
A final determination of the open water surface level is made manually with an interactive graphics program. Open water drafts resulting from this step are used to produce a continuous time series of the draft of open water. This time series of the surface level offset is then used to correct all drafts.
The width of the acoustic beam results in an ensonified window on the under-ice surface of about 10 m in diameter (for instruments moored at between 100 and 150 m deep). Within this window, ice draft can vary considerably. Travel time is measured as the time it takes for a pulse echo to exceed a threshold. Since the deepest part of the ice will return the pulse first, ice draft measurements are biased to larger values. This bias can be estimated using an estimate of the draft probability distribution. Ice draft from a large data set of Weddell Sea drill holes was analyzed and the overall mean bias was determined to be 0.20 +- 0.02 m. The mean bias was then subtracted from all ice draft measurements.
After processing raw data using the steps above, and assuming Gaussian distribution of errors, the total resulting error in ice draft measurements is about 4 cm (Strass, 1998).
In July 2009, H. Witte informed us of an error in the bias correction. This was the formula originally used to calculate the draft:
draft(corrected) = draft(measured) - bias*draft(measured)
where bias = 0.215
Further correspondence did not clarify what the correct bias should be.
Data are available via FTP.
Please direct all inquiries about the data set to NSIDC User Services:
NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449 USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
March 2012: A. Windnagel added a note in Step 7 Notes section.
NSIDC writers (firstname.lastname@example.org)