Vector Near field

Hi,

I am trying to verify that the vector is operating in the near-field and need to know the exact diameter of the ceramic that is vibrating. From Urick (1983, p.72), the equation would be r_o = A / L where r_o is the range where the transition from near field to far field occurs. A is for the radiating  face area of a  circular piston projector, r_o is the range within the transition zone at which the near field os considered to end and L is the acoustic wavelength. The equation is very sensitive to the value of A that is entered so I wanted to get it correct. If this equation does not apply to the transmit transducer, may I have the equation that applies.

This all goes to determining the actual width of the sampling volume. I am assuming that in the near field, there is no appreciable beam spreading or beam angle. Is this also correct?

Concerning the vertical height estimate of the sampling volume, Finelli et al. (1999) found that for Sontek ADVfield, the SNR is elevated beyond the actual quoted sample volume height in the setup software. He compared his measurements on a log and a linear scale (compared to the max SNR measured). The linear scale showed results near what the software quoted. Is the Nortek Vector sample volume similar to the Sontek in that the user should expect the sample volume to extend beyond the stated range to a similar degree when SNR are viewed as log values.

Cheers,
David

    Finelli, C. M., Hart, D. D. and Fonseca, D. M. 1999 Evaluating the spatial resolution of an acoustic Doppler velocimeter and the consequences for measuring near-bed flows. Limnology and Oceanography 44, 1793-1801.
    Urick, R. J. 1983 Principles of underwater sound. 3rd ed. McGraw-Hill, xiii, 423 pp.