A system analyzes radiation from a scene in a field of view that includes a gas cloud with absorption characteristics in a wavelength band. The system includes first and second devices. The first device includes a detector and produces pixel signals that include information associated with absorption of radiation in the gas cloud wavelength band. An image of the scene is formed on the detector based on the pixel signals. A non-predetermined region of the scene within the field of view in which the gas cloud is present is identified based on the pixel signals. The second device includes a detector and a lens, and receives the identified region of the scene. The system determines a distance between the identified region of the scene and the system based on the lens focus relative to the identified region of the scene in an image formed on the detector by the lens.
