A weighted least-squares algorithm was developed to fit a plane wave to arrival time differences yielding wave front direction and speed estimates. The algorithm was applied to acoustic pulses entering a sandy sediment through the water-sediment interface. An acoustic projector in the water column was used to insonify an array of sensors embedded in the sediment. Pulsed carriers, from 5 to 80 kHz, were projected toward the sediment interface at grazing angles below, near, and above the critical value. The plane-wave fit was found to good in all cases.