Patent ID: 8406471

Claim:
Apparatus for monitoring a region, comprising: an emitter for directing a beam of radiation comprising at least one predetermined characteristic into the region; an image capture device for obtaining at least one image of the region; and a processor for analysing the at least one image to detect variation of the at least one characteristic between the images, indicating presence of particles within the region, wherein the emitter emits a modulated beam of radiation into the region such that the emitted beam is modulated between an “on” state, in which the beam is emitted and an “off” state in which the beam is not emitted into the monitored region; and wherein the image capture device is arranged to: capture at least one image of the monitored region in a first plurality of time periods in which the beam of radiation is in the on state, to generate a one or more first images of the monitored region; and to capture at least one image of the monitored region in a second plurality of time periods in which the beam is in the off state to generate one or more second images of the monitored region, wherein the first and second time periods are at least partly interleaved with each other in time; and and wherein the processor is further configured to process at least one first image and at least one second image to detect an increase in radiation scattered from the beam of radiation.