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1.
Bishwajit Chakraborty Hans Werner Schenke Vijay Kodagali Rick Hagen 《Marine Geodesy》2002,25(1):19-26
Utilizing a hull-mounted, multinarrow beam echosounder onboard RV Polarstern, we measured variation of acoustic backscatter with incidence angles at two different sites in the Southern Oceans (Agulhas Plateau and the Riiser Larsen Sea). We modeled the data, using a composite roughness model, including water-sediment interface roughness and sediment volume roughness parameters. The model effectively uses the near normal incidence angle backscatter to determine the seafloor interface roughness parameters employing Helmholtz-Kirchhoff theory. Beyond 20° incidence angles, an application of Rayleigh-Rice theory is made by using a necessary splicing technique (combining both of the theories at 20° incidence angle). The estimated interface and volume roughness parameters are found to be in accordance with the known area geology. 相似文献
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Combining indicator trends to assess ongoing changes in exploited fish communities: diagnostic of communities off the coasts of France 总被引:1,自引:1,他引:1
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The conditional acid dissociation constants (pKa′) of two sulfonephthalein dyes, thymol blue (TB) and m-cresol purple (mCP), were assessed throughout the estuarine salinity range (0<S<40) using a tris/tris–HCl buffer and spectrophotometric measurement. The salinity dependence of the pKa′ of both dyes was fitted to the equations (25 °C, total proton pH scale, mol kg soln−1):The estimated accuracy of pH measurements using these calculated pKa′ values is considered to be comparable to that possible with careful use of a glass electrode (±0.01 pH unit) but spectrophotometric measurements in an estuary have the significant advantage that it is not necessary to calibrate an electrode at different salinities. pH was measured in an estuary over a tidal cycle with a precision of ±0.0005 pH unit at high (S>30) salinity, and ±0.002 pH unit at low (S<5) salinity. The pH increased rapidly in the lower salinity ranges (0<S<15) but less rapidly at higher salinities. 相似文献
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Abstract. Two sediment cores were collected in the southern Baltic Sea and sliced into 1.0cm-thick layers. Sediments of each layer were analysed for activities of 210Pb, 137Cs, 134Cs and for the density of meiobenthic organisms (meiofauna). Zones with the rapid mixing occur in the uppermost layers (0–3 cm) of the cores based on I34Cs profiles. The extent and density of meiofauna confirmed the rapid mixing and revealed layers with slow mixing (4–8 cm). Sedimentation rates were derived from 210Pb profiles below the mixing zones (1.21 and 1.72 mm a-I) and were confumed by 137Cs distribution. Of twenty-one major meiofauna taxa commonly found in the Baltic sediments, three were present in the cores. 相似文献