An airborne amplitude-modulated 1.57 μm differential laser absorption spectrometer: simultaneous measurement of partial column-averaged dry air mixing ratio of CO_2 and target range

摘要

Simultaneous measurements of the partial column-averaged dry air mixing ratio of CO_2 (XCO_2) and target range were demonstrated using airborne amplitu-demodulated 1.57 μm differential laser absorption spectrometer (LAS). The LAS system is useful for discriminating between ground and cloud return signals and has a demonstrated ability to suppress the impact of integrated aerosol signals on atmospheric CO_2 measurements. A high correlation coefficient (R) of 0.987 between XCO_2 observed by LAS and XCO_2 calculated from in situ measurements was obtained. The averaged difference in XCO_2 obtained from LAS and validation data was within 1.5 ppm for all spiral measurements. An interesting vertical profile was observed for both XCO_(2LAS) and XCO_(2val), in which lower altitude CO_2 decreases compared to higher altitude CO_2 attributed to the photosynthesis over grassland in the summer. In the case of an urban area where there are boundary-layer enhanced CO_2 and aerosol in the winter, the difference of XCO_(2LAS) to XCO_(2val) is a negative bias of 1.5 ppm, and XCO_(2LAS) is in agreement with XCO_(2val) within the measurement precision of 2.4 ppm (1 SD).