Possible corrections of spectral aerosol effects on measurements of atmospheric trace gas concentrations by differential absorption lidars

摘要

Some ways to reduce errors in measured concentrations of atmospheric trace gases by using the differential absorption lidar (DIAL) method are studied here. One requires the correction means owing to the following obvious fact. For a low concentration of an absorptive gas, the difference in signals at "on"- and "off-wavelengths utilized to sound the atmosphere would be small too. So the account for different optical spectral properties of atmospheric aerosols even at closely spaced "on"- and "off-wavelengths can be of great importance for such a case. This paper shows that essential changes in optical aerosol characteristics, for example, near 9 to 10 μm due to sulfate ions of atmospheric particles, can be a reason, which practically precludes a concentration of a trace gas in the "average" atmosphere from being determined to any acceptable error level. We consider here two experimental setups providing the DIAL measurements by path and sounding schemes, when reflection from a topographic target or aerosol backscatter delivers the signal to a receiver, respectively. Possible ways to correct differences in aerosol optical characteristics at "on"- and "off-wavelengths are discussed. To this end, model estimations of the spectral characteristics are used. Various models are considered to compare the errors in concentrations with and without the corresponding corrections. It is shown that for a number of path measurements one would succeed in the reduction of the errors. An empirical formula to correct measurements is given.