  For the first time, a globally convergent numerical method is developed and
Lipschitz stability estimate is obtained for the challenging problem of travel
time tomography in 3D for formally determined incomplete data. The semidiscrete
case is considered meaning that finite differences are involved with respect to
two out of three variables. First, Lipschitz stability estimate is derived,
which implies uniqueness. Next, a weighted globally strictly convex
Tikhonov-like functional is constructed using a Carleman-like weight function
for a Volterra integral operator. The gradient projection method is constructed
to minimize this functional. It is proven that this method converges globally
to the exact solution if the noise in the data tends to zero.
