1. A method comprising: obtaining an acoustic impedance of a subsurface layer based on time a reflected acoustic wave reaches Earth's surface; obtaining a density measurement and a sonic velocity measurement of the subsurface layer from one or more tools at a depth in a wellbore; estimating acoustic impedance of the subsurface layer based on the density measurement and the sonic velocity measurement; and comparing the acoustic impedance estimated from the density measurement and the sonic velocity measurement to the acoustic impedance from the reflected acoustic wave.