Inter-manufacturer Difference and Temperature Dependency of the Fall-Rate of T-5 Expendable Bathythermograph

The fall-rate of the T-5 expendable bathythermograph (XBT) produced by Tsurumi Seiki (TSK) Co., Ltd and that by Sippican Inc., are intercompared by a series of contemporaneous and colocated measurements with conductivity-temperature-depth (CTD) profilers. It is confirmed that the fall-rates of the two manufacturers' T-5 differ by about 5 percent, despite the fact that they had been believed to be identical for many years. The cause of the difference is discussed on the basis of a detailed cross-examination of the two T-5 models. It is found for the first time that the two models are different in several respects. The manufacturer's fall-rate equation is only applicable to the Sippican T-5, for which Boyd and Linzell's (1993) equation seems to be slightly more accurate. Kizu et al.'s (2005) equation gives a clearly less biased depth than the manufacturers' equation for the TSK T-5. It is also found that the fall-rates of both T-5 models are dependent on water temperature, perhaps because of viscosity. The temperature-dependency of the fall-rate of the TSK T-5 is larger than that of the Sippican T-5.     

Reduction of radar cross section by multiple passive impedance loadings

A general formulation to reduce scattering from conducting objects by multiple passive impedance loadings is derived. The method of moments is used to analyze the conducting objects, and biquadratic programming as an iterative minimization method is used to find the optimum passive impedance. Computer programs to reduce the bistatic radar cross section for arbitrarily shaped thin-wire scatterers by multiple passive impedance loadings have been developed. Some calculated results for a straight wire, a circular loop, and a rectangular wire frame are shown. It is found that multiple loadings are much more effective to control scattering than a single loading.