Measurement of solids is a challenge for a number of reasons. The solids surface is uneven and shifts as the silo is filled or emptied. Silos often have a dusty environment which can obstruct the measurement reading for many technologies. Lastly, some materials tend to build up and stick on walls, occupying space that may not truly be available for production. All these parameters make it difficult to know how much material is in the silo and how much capacity is available for additional material.