1. An apparatus for remote light-based detection of an analyte in a remote target region, comprising: a reference substance identical with the analyte; a light beam unit that emits a light beam of a tunable wavelength towards the target region to be analysed and towards the reference substance for interacting with the reference substance; a light beam control means for controlling 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 that detects light from the target region and generates analytical signals during the detection periods, a reference detection unit that detects light which has interacted with the reference substance and generates reference signals during the detection periods; and an analysing means for analysing a similarity between 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 by calculating a cross-correlation function between a calculated reference function derived from the reference signals and a calculated analytical function derived from the analytical signals, calculating an autocorrelation function based on the calculated reference function, and calculating the concentration of the analyte based on the cross-correlation function and the autocorrelation function.