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  • 1
    Series available for loan
    Series available for loan
    Kingston : Antarctic Division, Dept. of Science
    Associated volumes
    Call number: ZSP-124-25
    In: ANARE research notes
    Description / Table of Contents: This Research Note details the mathematics behind the development of a program to calculate the impulse function relating two arrays of data. These data arrays are discrete samples of the proposed driving and driven functions. The program is tested for its susceptibility to noise and non-linear variations between the input functions. The impulse function program and relevant test programs are listed and their use described.
    Type of Medium: Series available for loan
    Pages: iv, 42 S. : Ill.
    ISBN: 0642074534
    Series Statement: ANARE research notes 25
    Branch Library: AWI Library
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  • 2
  • 3
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    In:  EPIC3WOCE Newsletter, 36, Institute of Oceanographic Sciences, WOCE Int. Project Office, Southampton, UK, 39 p.
    Publication Date: 2019-07-16
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , notRev
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  • 4
    Publication Date: 2019-07-17
    Description: Airborne, ship-borne and surface low-frequency electromagnetic (EM) methods have become widely applied to measure sea-ice thickness. EM responses measured over sea ice depend mainly on the sea-water conductivity and on the height of the sensor above the sea-icesea-water interface, but may be sensitive to the sea-ice conductivity at high excitation frequencies. We have conducted in situ measurements of direct-current conductivity of sea ice using standard geophysical geoelectrical methods. Sea-ice thickness estimated from the geoelectrical sounding data was found to be consistently underestimated due to the pronounced vertical-to-horizontal conductivity anisotropy present in level sea ice. At five sites, it was possible to determine the approximate horizontal and vertical conductivities from the sounding data. The average horizontal conductivity was found to be 0.017 Sm1, and that in the vertical direction to be 912 times higher. EM measurements over level sea ice are sensitive only to the horizontal conductivity. Numerical modelling has shown that the assumption of zero sea-ice conductivity in interpretation of airborne EM data results in a negligible error in interpreted thickness for typical level Antarctic sea ice.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 5
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    In:  EPIC3Extended abstracts, 11th European Meeting of Environmental and Engineering Geophysics (EAGEs Near Surface 2005), A022, Palermo, Italy.
    Publication Date: 2019-07-17
    Description: Semi-empirical methods are routinely used for Helicopter Electromagnetic (HEM) sea ice thickness mapping. Although these methods yield sufficiently accurate thickness data, it is of interest to determine whether formal one-dimensional (1D) geophysical inversion could yield improved results. If both the thickness and the ice conductivity could be mapped, the results could be used to estimate glaciological parameters such as the age of the sea ice. Sea ice conductivity data could also be potentially used to estimate the strength of the ice sheet, which would be valuable information for planning of icebreaking operations. By investigating synthetic and field data we show that, in the case of level sea ice of thickness up to 2 m, the accuracy of our HEM system is not high enough to sense the small conductivity variations arising from the age of the ice. Sea ice conductivity has a stronger influence on the measured HEM responses in areas of thick, deformed sea ice (pressure ridges), where bulk conductivity is higher as a result of the large seawater-filled porosity. Synthetic three-dimensional HEM data generated for pressure ridge models has shown that the 1D interpretation methods conventionally used for interpretation of sea ice thickness overestimate the true bulk conductivity at 3D features.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 6
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    In:  EPIC3Geophysics, 71(2), G63-G72
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 7
    Publication Date: 2019-07-16
    Description: Accuracy and precision of helicopter electromagneticHEM sounding are the essential parameters for HEM seaicethickness profiling. For sea-ice thickness research, thequality of HEM ice thickness estimates must be better than10 cm to detect potential climatologic thickness changes.Weintroduce and assess a direct, 1D HEM data inversion algorithmfor estimating sea-ice thickness. For synthetic qualityassessment, an analytically determined HEM sea-ice thicknesssensitivity is used to derive precision and accuracy. Precisionis related directly to random, instrumental noise, althoughaccuracy is defined by systematic bias arising fromthe data processing algorithm. For the in-phase component ofthe HEM response, sensitivity increases with frequency andcoil spacing, but decreases with flying height. For small-scaleHEM instruments used in sea-ice thickness surveys, instrumentalnoise must not exceed 5 ppm to reach ice thicknessprecision of 10 cm at 15-m nominal flying height. Comparableprecision is yielded at 30-m height for conventional explorationHEM systems with bigger coil spacings. Accuracylosses caused by approximations made for the direct inversionare negligible for brackish water and remain better than10 cm for saline water. Synthetic precision and accuracy estimatesare verified with drill-hole validated field data fromEast Antarctica, where HEM-derived level-ice thicknessagrees with drilling results to within 4%, or 2 cm.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 8
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    In:  EPIC3Extended abstracts, 10th European Meeting of Environmental and Engineering Geophysics (EAGEs Near Surface 2004), A037, Utrecht, The Netherlands.
    Publication Date: 2019-07-16
    Description: Since 2001, the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven(AWI) has operated a purpose built, unique HEM system to map sea ice thickness in theArctic and Antarctic. To determine the sea ice thickness from the measured EM field we usean empirical curve fitting approach. The master curve is tuned for every flight leg usingmeasurements over open water between the ice floes in leads or polynyas. The level icethickness, which is a key value for sea ice science and climate research can be derived with anaccuracy of a few centimeters.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 9
    Publication Date: 2014-04-15
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , peerRev
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  • 10
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    Gulf Publishing Company | Houston, TX
    In:  http://aquaticcommons.org/id/eprint/14157 | 9596 | 2020-08-31 20:22:11 | 14157 | Galveston Bay Information Collection
    Publication Date: 2021-06-24
    Description: Based on their characteristic properties, the water masses of the Gulf of Mexico and their vertical stratification are discussed. The T-S relationships specific to the region are presented. For the basin waters, below a sill depth of about 2000 m, the potential temperature, salinity and dissolved-oxygen concentrations show no measurable horizontal variation, although weak vertical density gradients evidence slight positive stability. Variations in the characteristics of the water in the following layers are shown, and the likely origins of these water masses are identified: North Atlantic Deep Water, Subantarctic Intermediate Water, oxygen minimum layer and Subtropical Underwater. For the winter, season, the property distributions in the mixed surface layers are described. On the basis of dynamic computations and GEK measurements, the general winter circulation patterns within the Gulf are examined. The mode most often observed in the eastern Gulf is one dominated by the Loop Current; water enters through Yucatan Strait as the Yucatan Current and flows in a clockwise loop which extends well in the Gulf and exits via Florida Strait. The extent of penetration and location of this loop is quite variable. In other seasons, large current rings are known to separate from the Loop Current. In contrast, the winter circulation in the western Gulf seems more predictable; it consists primarily of a clockwise cell centered over the western central Gulf, having broad westward flow for its southern limb, a narrow east northeastward flow for its northern limb and flanked to the north by a west-southwestward current along the outer Texas-Louisiana shelf.
    Keywords: Atmospheric Sciences ; Oceanography ; oceanography ; winter circulation
    Repository Name: AquaDocs
    Type: monograph
    Format: application/pdf
    Format: application/pdf
    Format: 2-51
    Format: 49
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