Potential CO ₂ measurement capabilities of a transportable Near Infrared Laser Heterodyne Radiometer (LHR)

Abstract. In this study, heterodyne detection enables high spectral resolution, which in turn enhances the vertical sensitivity of ground-based CO2 measurements. The system's compact and portable design makes it particularly well-suited for deployment 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 an 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 (Monitoring of Atmospheric composition and Greenhouse gases through multi-Instruments Campaigns) campaigns focused on greenhouse gas monitoring and the validation of current and future space missions such as MicroCarb and CO2M.