In underground salt mining, salt rocks are fed through a primary crusher in the underground mine prior to being stored in large underground silos. The primary crushed rock storage silo feeds a secondary crusher on the surface, and therefore needs to be monitored to provide consistent production supply. Since underground silos are usually created by controlled explosions, the walls are not smooth, making accurate measurement of the stored salt rocks very difficult. Early detection of build-up that forms inside the silo is important so operators can allow timely maintenance and prevent unexpected interruptions to production. Accurate monitoring also reduces the risk of material collapse to the bottom of the silo, which could cause damage to the silo, the crusher, and other mechanical parts.