The inverse scheme is not optimized under the formalized condition in solving an inverse problem of ocean acoustic tomography. But if how the travel time bias can affect the reconstructed profiles is examined, it is useful to determine the optimal bias for each inversion. There are two methods to determine this bias. One is to minimize the variance of the sound-speed anomaly as a function of travel time bias. The other is to use the formula derived by the minimization of the variance of the difference of true and estimated sound-speed anomalies. Even though both results must agree with each other in principle, they are not always the same. In examining the discrepancy, the assumption can be made that the inverse scheme is optimal which minimizes the difference of both biases. Moreover, the travel time bias makes it possible to treat with barotropic mode of current and temperature separated from baroclinic modes.