A method of remote sensing of <sup>13</sup>СО<sub>2</sub> to <sup>12</sup>СО<sub>2</sub> ratio in the atmosphere using high resolution transmittance IR spectra.
Monitoring of content of isotopes of carbon dioxide in the atmosphere is one of the most important tasks of control carbon cycle and global climate change. A method of remote sounding of column averaged <sup>13</sup>СО<sub>2</sub> to <sup>12</sup>СО<sub>2</sub> ratio in the atmosphere is proposed for the first time. The method uses ratio of optical depths of homologous couple of lines of <sup>13</sup>СО<sub>2</sub> and <sup>12</sup>СО<sub>2</sub> from high resolution transmittance spectra of solar radiation in the atmosphere within the range 6100-6300 cm<sup>-1</sup> which depends only on the columnar ratio <sup>13</sup>СО<sub>2</sub>/<sup>12</sup>СО<sub>2</sub> and does not depend on variations of temperature profile of the atmosphere and solar zenith angle. A possibility of application of the method to atmospheric transmittance spectra measured with modern FTIR in cloudless and «aerosol free» atmosphere is discussed.