Development of a laser heterodyne spectroradiometer for high-resolution measurements of CO 2 , CH 4 , H 2 O and O 2 in the atmospheric column

Abstract

We have developed a portable near-infrared laser heterodyne radiometer (LHR) for quasi-simultaneous measurements of atmospheric carbon dioxide (CO 2 ), methane (CH 4 ), water vapor (H 2 O) and oxygen (O 2 ) column absorption by using three distributed-feedback diode lasers as the local oscillators of the heterodyne detection. The developed system shows good performance in terms of its high spectral resolution of 0.066 cm −1 and a low solar power detection noise which was about 2 times the theoretical quantum limit. Its measurement precision of the column-averaged mole fraction for CO 2 and CH 4 is within 1.1%, based on the standard deviation from the mean value of the retrieved results for a clean sky. The column abundance information of the O 2 is used to correct for the variations and uncertainties of atmosphere pressure, the solar altitude angle, and the prior profiles of pressure and temperature. Comparison measurements of daily column-averaged atmospheric mole fractions of CO 2 , CH 4 and H 2 O, between our developed LHR and a greenhouse gas observing satellite, show a good agreement, which proves the reliability of our developed system.