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Validating and improving the global atmospheric transport model, therefore, requires precise measurement of the CO2 concentration profile. The differential absorption lidar (DIAL) is thought to be one of the best methods for observing the vertical distribution of greenhouse gases. One of its main advantages over other passive methods is its capacity for taking continuous measurements that provide high spatial and temporal resolutions of CO2. We had developed a ground based direct detection 1.6 μm DIAL to achieve measurements of vertical CO2 profiles. As the spectra of absorption lines of any molecules are influenced basically by the air temperature, it is important to measure the air temperature simultaneously. Then, we have improved the 1.6 μm DIAL system for simultaneous measurements of the CO2 concentration and temperature profiles in the lower-atmosphere. We conducted a field experiment to compare the new DIAL measurements with in situ sensor measurements. An open-path CO2 gas analyzer (LICOR. Inc., LI-7500) and temperature sensor (T&D TR-72Ui) were installed at the top of the building at a height of 42 m. The average difference in the CO2 concentration measured by the DIAL and LI-7500 was −0.01 ± 2.1 ppm. The average difference in the atmospheric temperature measured by the DIAL and TR-72Ui was −0.10 ± 0.28 °C. The new DIAL system is, therefore, capable of performing highly accurate vertical CO2 concentration and atmospheric temperature measurements.
We also conducted some continuous observations of CO2 concentration and temperature profiles in the lower atmosphere. In this paper, daily variation of CO2 concentration and temperature profiles are reported. We found that the accuracy of the CO2 concentration profiles measured with the new DIAL is improved significantly by the air temperature measurement.
This work was financially supported by the System Development Program for Advanced Measurement and Analysis of the Japan Science and Technology Agency.
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