A method comprising: receiving sensor data generated by one or more radar sensors in response to sensing a structure; filtering the sensor data, the filtering comprising: identifying a first portion of the sensor data as edge data, the edge data describing a structural feature of the structure and indicating a first instance where said structural feature is sensed; and identifying a second portion of the sensor data as reverberation data describing the same structural feature as that described by the edge data; and generating image data for a filtered image of the structure from the sensor data, the image data generated from data identified as edge data but not from data identified as reverberation data; characterised in that the method further comprises: detecting a leading edge (440a, 440b) of the edge data, the leading edge describing a first portion of a first structural feature; detecting a non- leading edge (442a, 442b) of the edge data, the non- leading edge describing a second portion of the same structural feature, the second portion further away from the sensors; determining that an intensity of the non- leading edge (442a, 442b) exceeds an intensity of the leading edge (440a, 440b); increasing the intensity of the leading edge (440a, 440b) to a level equal to the intensity of the non- leading edge (442a, 442b); and decreasing the intensity of the non- leading edge (442a, 442b) to filter out the non-leading edge (442a, 442b). receiving sensor data generated by one or more radar sensors in response to sensing a structure; filtering the sensor data, the filtering comprising: identifying a first portion of the sensor data as edge data, the edge data describing a structural feature of the structure and indicating a first instance where said structural feature is sensed; and identifying a second portion of the sensor data as reverberation data describing the same structural feature as that described by the edge data; and identifying a first portion of the sensor data as edge data, the edge data describing a structural feature of the structure and indicating a first instance where said structural feature is sensed; and identifying a second portion of the sensor data as reverberation data describing the same structural feature as that described by the edge data; and generating image data for a filtered image of the structure from the sensor data, the image data generated from data identified as edge data but not from data identified as reverberation data; characterised in that the method further comprises: detecting a leading edge (440a, 440b) of the edge data, the leading edge describing a first portion of a first structural feature; detecting a non- leading edge (442a, 442b) of the edge data, the non- leading edge describing a second portion of the same structural feature, the second portion further away from the sensors; determining that an intensity of the non- leading edge (442a, 442b) exceeds an intensity of the leading edge (440a, 440b); increasing the intensity of the leading edge (440a, 440b) to a level equal to the intensity of the non- leading edge (442a, 442b); and decreasing the intensity of the non- leading edge (442a, 442b) to filter out the non-leading edge (442a, 442b). detecting a leading edge (440a, 440b) of the edge data, the leading edge describing a first portion of a first structural feature; detecting a non- leading edge (442a, 442b) of the edge data, the non- leading edge describing a second portion of the same structural feature, the second portion further away from the sensors; determining that an intensity of the non- leading edge (442a, 442b) exceeds an intensity of the leading edge (440a, 440b); increasing the intensity of the leading edge (440a, 440b) to a level equal to the intensity of the non- leading edge (442a, 442b); and decreasing the intensity of the non- leading edge (442a, 442b) to filter out the non-leading edge (442a, 442b).