| Abstrakt: |
NASA has been conducting several studies for quantifying and monitoring atmospheric CO2 including the Orbiting Carbon Observatory space-based missions. To complement CO2 passive sensing, the National Research Council recommended active remote sensing techniques, which are valuable for validating current space-based measurements and potential future missions. Recently, a 2- $\mu \text{m}$ triple-pulse integrated path differential absorption (IPDA) lidar was developed for simultaneous and independent measurements of atmospheric CO2 and H2O. This instrument was operated at fixed wavelengths, precisely selected to avoid mutual interferences. Focusing on optimized CO2 measurements, this instrument has been updated to operate in double-pulse mode. The objective is to demonstrate high-precision and high-accuracy column CO2 measurements using tunable on-line wavelength suitable for adaptive targeting. Statistical analysis of long record CO2 field measurement and retrieval results in 1.92-ppm accuracy, equivalent to 0.44% systematic error, and 1.66-ppm precision, equivalent to 0.39% random error. Referring to the R30 CO2 absorption line, this was achieved using an on-line laser frequency offset of 1 GHz, a 5.2% target reflectivity, and 10-s average. The record indicated a better than 99% data success rate. Tuning the on-line frequency offset to 0.5 GHz results in 1.11- and 0.33-ppm measurement accuracy and precision, equivalent to 0.26% and 0.08% systematic and random errors, respectively, obtained using 13.6% target reflectivity. Range measurements indicate 0.7-m precision and 0.2-m accuracy. These results demonstrate the reliability of atmospheric CO2 measurements with high precision and high accuracy, using the pulsed 2- $\mu \text{m}$ IPDA lidar. [ABSTRACT FROM AUTHOR] |
