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Articles by K. Iida
Total Records ( 2 ) for K. Iida
  M Hirose , T Mukai , D Hwang and K. Iida
 

Hirose, M., Mukai, T., Hwang, D., and Iida, K. 2009. The acoustic characteristics of three jellyfish species: Nemopilema nomurai, Cyanea nozakii, and Aurelia aurita. – ICES Journal of Marine Science, 66: 1233–1237.

Reports about jellyfish damaging nets and reducing fish catches are increasing, and data on the abundance and distribution of various jellyfish species are needed to forecast where and when their blooms will happen. Acoustic techniques can be used to obtain this information if the acoustic characteristics of the targets are known. This is a study of acoustic scattering from three jellyfish species: Nemopilema nomurai (order Rhizostomeae), Cyanea nozakii (Semaeostomeae), and Aurelia aurita (Semaeostomeae). Target strength (TS) at 38, 120, and 200 kHz, specific density, and sound speed were measured with live specimens. Specific densities were measured using the displacement–volume–weight and the dual-density methods. The sound speeds were estimated using the time-of-flight method. The reduced TS (RTS), i.e. the TS normalized by bell area, was smaller for N. nomurai (bell diameter range 19–38 cm) than for C. nozakii (bell diameter range 30–40 cm), and the differences in RTS between the species were 17.8, 12.6, and 5.8 dB at 38, 120, and 200 kHz, respectively. The respective sound-speed contrast h and density contrast g were 1.0008 ± 0.009 (mean ± s.d.) and 1.004 ± 0.015 for N. nomurai; 1.038 and 1.073 for one C. nozakii; and 1.0001 ± 0.025 and 0.989 ± 0.019 for A. aurita.

  T. Lihan , M.A. Mustapha , S.A. Rahim , S. Saitoh and K. Iida
  Freshwater discharge from rivers into the ocean is an important element of the dynamics in coastal areas. River discharge from land that includes chlorophyll a, nutrients, sediments and pollutants have been identified as one of the major causes of deterioration of the coastal water. The objective of this study was to examine the relationship between river discharge and variability of chlorophyll a concentration in plume area using satellite imagery. Satellite ocean color and Sea Surface Temperature (SST) imagery were used to present the synoptic quantification of chlorophyll a variability on seasonal and interannual timescales for the plume area of Tokachi River, Japan. Five years (1998 to 2002) of SeaWiFS local area coverage, AVHRR imagery and surface wind were analyzed using default NASA coefficients and community-standard algorithms as implemented by SeaDAS. The chlorophyll a climatology seasonal pattern showed seasonal cycles, first peak in spring and second peak in late summer to early autumn. Elevated chlorophyll a concentration demonstrates seasonal cycles and interannual variability are present around plume area associated with variation of river discharge. Elevated chlorophyll a concentration in offshore area was seen to be influenced by low sea surface temperature and wind stress.
 
 
 
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