Comments on "Bearings-only and Doppler-bearing tracking using instrumental variables"

The work carried out by Y.T. Chan and S.W. Rudnicki [ibid., vol. 28, pp. 1076-82, 1992] is very useful for studies in underwater target motion analysis. They presented a simple procedure so that the dimension of the target state vector need not be increased. While implementing their work, I tried to rederive the equations and found that there is a confusion in one of the equations, which I discuss here.