A height measurement apparatus comprising an array of differential pressure sensors, each differential pressure sensor comprising a reference outlet and a measurement outlet, the reference outlet being a predetermined distance from a reference surface, and each differential pressure sensor further comprising an inlet configured to provide pressurized gas for the reference outlet and the measurement outlet. A flexible membrane is positioned such that a reference side of the flexible membrane is in fluid communication with the reference outlet and a measurement side of the flexible membrane is in fluid communication with the measurement outlet. The flexible membrane is configured to move when a pressure change occurs at the measurement outlet and a detector is configured to monitor the movement of the flexible membrane.