Perspective of remote optical measurement techniques (ROMTs)

This article presents an intercomparison between four different ROMTs: Differential Optical Absorption Spectroscopy (DOAS), DIfferential Absorption LIDAR (DIAL), Fourier Transform Infrared Spectroscopy (FTIR), and Tunable Diode Laser Absorption Spectroscopy (TDLAS). The main focus is on the TDLAS technique, where the main laser-diode typologies and modulation schemes, namely, wavelength modulation spectroscopy (WMS) and frequency modulation spectroscopy (FMS), are reviewed. At present, new promising modulation schemes with range resolution capability are being investigated. Among them, analog frequency modulation (FM) and digital pseudo-random schemes are discussed.