Abstract: A measurement device, such as a laser radar, is described that comprises a transmitter portion for transmitting radiation to a remote probe volume, a receiver portion for detecting radiation returned from the remote probe volume and a processor for analysing the detected return radiation. The device is suitable for transmitting and receiving radiation through a window portion having associated window cleaning apparatus (e.g. wiper 62) for cleaning said window portion in response to a cleaning activation signal. The processor is arranged to generate a cleaning activation signal for activating window cleaning apparatus when the properties of said detected return radiation are indicative of a reduction in transmission through at least part of said window portion. In one embodiment, a conically scanned lidar is described that generates a cleaning activation signal when the power of detected return radiation varies as a function of the angle of transmission of radiation from the device.

Abstract: A measurement device, such as a laser radar, is described that comprises a transmitter portion for transmitting radiation to a remote probe volume, a receiver portion for detecting radiation returned from the remote probe volume and a processor for analysing the detected return radiation. The device is suitable for transmitting and receiving radiation through a window portion having associated window cleaning apparatus (e.g. wiper 62) for cleaning said window portion in response to a cleaning activation signal. The processor is arranged to generate a cleaning activation signal for activating window cleaning apparatus when the properties of said detected return radiation are indicative of a reduction in transmission through at least part of said window portion. In one embodiment, a conically scanned lidar is described that generates a cleaning activation signal when the power of detected return radiation varies as a function of the angle of transmission of radiation from the device.