Frequency-division multiplexing intensity-modulated laser heterodyne radiometer for simultaneous measurements of atmospheric CO2 and CH4 columns

Abstract

Frequency-division multiplexing intensity-modulated (FDM-IM) laser heterodyne detection has been proposed and applied to measure atmospheric CO₂ and CH₄ columns. System performance analysis indicates that the system noise level is approximately ten times lower than the theoretical quantum limit. The developed laser heterodyne radiometer (LHR) was used to continuously monitor CO₂ and CH₄ column concentrations in Hefei, China, for two days, achieving a measurement precision of approximately 0.6 %. Compared with traditional single channel LHR, the relative error margin is maintained within 0.1 %. The FDM-IM LHR demonstrates comparable performance to traditional LHRs while enabling simultaneous measurement of multiple atmospheric components and significantly reducing system complexity and costs.