Apparatus for remote laser-based detection of a analyte in a remote target region; comprising a reference container for housing a reference substance identical with the analyte; a laser unit which constituted to emit a laser beam of a tuneable wavelength towards the target region to be analysed and along a reference path which passes through the reference container for detecting the reference substance; a laser control means constituted to control wavelength of the laser beam during detection periods such that the laser wavelength is changed to allow detection of an optical absorption profile 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 laser light passed through the reference container 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.