A compact, lightweight heterodyne NIR spectro-radiometer suitable for ground-based atmospheric sounding by direct spectro-radimetry of Sun spectrum with spectral resolutionl/dl ~ 5*107 has been used for precise measurements and vertical profiling of methane and carbon dioxide. Highly stabilized DFB laser was used as local oscillator, while single model quartz fiber Y-coupler served as a diplexer. Radiation mixed in the single mode fiber was detected by quadratic detector using p-i-n diode within the bandpass of ~10 MHz. Wavelength coverage of spectral measurement was provided by sweeping local oscillator frequency in the range 1,1 см-1. With the exposure time of 15 min, the absorption spectrum of the atmosphere over Moscow has been recorded with S/N ~ 300.
We retrieved methane vertical profile using Tikhonov method of smooth functional, which takes into account a priori information about first guess profile. The reference to model methane profile means that the regularization procedure always selects a priori values unless the measurements contradict this assumption.
The retrieved methane profile demonstrates higher abundances in the lower scale height compared to the assumed model profile, well expected in the megalopolis center. The retrievals sensitivity is limited by 10 ppb, with the exception of the lower part of the profile where the tendency to lower values is revealed. Thus the methane abundance variations may be evaluated with relative accuracy better than 1%, which fits the requirements of greenhouse gas monitoring.
The CO2 profile has also been retrieved with the accuracy sufficient for analyzing regional sources of greenhouse gases.