Spatial distribution of methane over Lake Baikal surface.

The results of application of a high sensitivity methane laser detector to investigations of the methane concentration in the atmosphere over Baikal lake are presented as well as methane flows from the water into the atmosphere. The measurements were conducted at a stationary station and aboard the research vessel "Vereschagin" during two summer expeditions in 2003 and 2004. Mean background concentration was equal to (2.00+/-0.16) ppm in August 2003 and (1.90+/-0.07) ppm in June 2004. The areas of methane emission through the water's surface are found to be distinctly localized and to have a characteristic size of about 150-300 m in diameter. The methane concentration in the centers of these areas can reach approximately 27 ppm. Methane flows into the atmosphere in some Baikal regions were measured as well.

Two-channel opto-acoustic diode laser spectrometer and fine structure of methane absorption spectra in 6070-6180 cm-1 region.

We describe the hardware and software of the high-sensitive two-channel opto-acoustic spectrometer with a near infrared diode laser. A semiconductor TEC-100 laser with outer resonator generates a continuous single-frequency radiation in the range of 6040-6300 cm-1 with spectral resolution better that 10 MHz. The newly designed model of photo-acoustic cells in the form of a ring type resonator was used in the spectrometer, and the system allows the measurement of a weak absorption coefficient equal to 1.4x10(-7) cm-1 Hz-1/2 with a laser radiation power of 0.003 W. The methane absorption spectra within a range of 6080-6180 cm-1 were measured with a spectral resolution of 10 MHz and the signal to noise ratio more than 10(3). Six hundred absorption lines were recorded, which is twice as many as in HITRAN-2004. The accurate measurements of the half-width and shift of methane unresolved triplet R3 of 2nu3 band permit us to determine values of the broadening and shift coefficients for CH4-air, CH4-N2, and CH4-SF6 mixtures.