1. Apparatus for remote light-based detection of a analyte in a remote target region; comprising a reference substance identical with the analyte; a light beam unit which is constituted to emit a light beam of a tuneable wavelength towards the target region to be analysed and towards the reference substance for interacting with the reference substance; a light beam control means constituted to control wavelength of the light beam during detection periods such that the light beam wavelength is changed to allow detection of optical properties of the analyte during detection periods; an analytical detection unit which detects light from the target region and generates analytical signals during the detection periods, a reference detection unit which detects light which has interacted with the reference substance and generates reference signals during the detection periods; and an analysing means constituted to analyse the similarity of the analytical and reference signals or of one or more calculated functions respectively calculated from the analytical and reference signals for determining the concentration of the analyte in the target region.