Unique greenhouse gas meter developed

Researchers have developed a high-resolution meter to gauge the concentration of gases in the atmosphere with unparallelled precision - and it is 10 times more accurate than a similar meter created by NASA.
Researchers from the Moscow Institute of Physics and Technology's Laboratory for the Spectroscopy of Planetary Atmospheres said the infrared spectrum radiometer is 100 times more precise than the best available near-infrared spectrometers.
The device is 10 times more accurate than a meter created on a similar principle recently described by NASA's Goddard Center, they said.
Tracking down carbon dioxide, methane and other gases with simultaneous determination of their concentrations at different altitudes is necessary, in particular, for research into global warming.

The new meter is far less susceptible to external disturbances compared with existing analogues. Its performance depends to a lesser extent on vibration, humidity and exposure to both low and high temperatures, researchers said.
They explained that the meter uses the heterodyne principle, known for over 100 years.

The essence of the method could be best described as follows: a received signal is added to a reference signal to form an intermediate frequency signal, researchers said.
The converted signal is much easier to process, namely to amplify and to filter. Moreover, when the frequency of the reference signal is sufficiently stable, extremely high sensitivity can be achieved.

The only problem is that a signal of very high frequency, whether it is infrared or optical, is not so easy to add to the reference source - it must be very stable and at the same time emit radiation of high intensity.
The first heterodyne radios, operating at megahertz frequencies, were created in the early 20th century while in the terahertz sphere heterodyne devices appeared only recently.
For near-infrared radiation, whose frequency is a few hundred times greater, the task of combining the signals appeared to be compounded by a number of technical difficulties.
Calculations showed that a more 'touchy' device is needed for a heterodyne signal in the near infrared radiation spectrum.

Even a shift of a few hundredths of a wavelength (ie a couple of dozen nanometers) could be critical, but eventually the researchers and their colleagues from the Moscow-based General Physics Institute managed to create a heterodyne near-infrared detector, in which a key role was played by laser stabilisation.
The meter is described in an article published in the journal Optics Express.