Potential CO₂ measurement capabilities of a transportable Near Infrared Laser Heterodyne Radiometer (LHR)

Abstract. Heterodyne detection stands as a powerful method for enhancing sensitivity limits and attaining exceptional resolution. It also offers the advantage of being transportable and the ability to make it more compact which makes it favorable for ground-based remote sensing in field campaigns. An all-fiber coupled laser heterodyne radiometer (LHR), using a wideband tunable external cavity diode laser (1520–1580 nm) as local oscillator laser was developed for CO₂ measurements. Optimal absorption lines and transmission spectra of the LHR was achieved by using a balanced photodetector to suppress the relative intensity noise of the local oscillator laser. This work aims to quantify how the LHR contributes to measuring tropospheric CO₂ abundances in the atmospheric column from the ground. Here, we demonstrate the LHR’s ability to measure CO₂ vertical profiles through a extensive analysis of information content, channel selection, and error budget estimation. This comprehensive analysis relies on the radiative transfer model ARAHMIS, developed at the Laboratoire d’Optique Atmosphérique (LOA). Additionally, we present a comparison of the LHR with other ground-based instruments, such as the EM27/SUN and the IFS125HR from the TCCON network. Furthermore, this work supports ongoing MAGIC campaigns focused on greenhouse gas monitoring and the validation of current and future space missions such as MicroCarb and FORUM.