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
Simultaneous measurements of the partial column-averaged dry air mixing ratio of CO 2 (XCO 2) and target range were demonstrated using airborne amplitude-modulated 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).