There are unfortunately two different definitions of the wavenumber. French (1971, p. 214) uses the definition(1)
where is the wavelength. However, as French notes, it is more common in theoretical physics to use the definition(2)
which is the convention followed in this work. The term "wavenumber" is sometimes also written out as two separate words (French 1971, p. 214).
Jensen, F. B.; Kuperman, W. A.; Schmidt, H.; Portor, M. B. Computational Ocean Acoustics. New York: Springer-Verlag, 1994.
French, A. P. Vibrations and Waves. New York: W. W. Norton, 1971.© 1996-2007 Eric W. Weisstein