Described is a device for detecting a surface of bulk materials, the device including: a transmitter unit having a radiation direction for transmitting a measuring signal, a receiver unit for receiving a measuring signal reflected on the surface of the bulk material, a control and evaluation unit for controlling the alignment of the radiation direction and for evaluating the received measuring signal, and an alignment arrangement for aligning the transmitter unit. The alignment arrangement includes at least one connecting element for connection to the transmitter unit, at least one bearing element, and at least one positioning member. The connecting element is pivotably connected to the bearing element via the positioning member. The alignment of the transmitter unit can be changed by the positioning member. The positioning member includes a shape memory element that actively changes its shape under variations of an influencing parameter.