By remotely "combing" the atmosphere with a custom laser-based instrument, researchers from the National Institute of Standards and Technology (NIST), in collaboration with researchers from the National Oceanic and Atmospheric Administration (NOAA), have developed a new technique that can accurately measure—over a sizeable distance—amounts of several of the major "greenhouse" gases implicated in climate change.
The technique potentially could be used in several ways to support research on atmospheric greenhouse gases. It can provide accurate data to support ongoing and future satellite monitoring of the composition of the atmosphere. With development, more portable systems based on the technology could provide very accurate, continuous regional monitoring of these gases over kilometer scales—a capability lacking with current monitoring techniques.
Photo illustration of NIST experiment using a pair of laser frequency combs (depicted as rainbow-colored cartoons) to detect the simultaneous signatures of several 'greenhouse' gases along a 2-kilometer path between a NIST laboratory roof and a nearby mesa. Each comb 'tooth' represents a different frequency of light. To identify gases in the atmosphere, researchers measured the amount of comb light absorbed at different frequencies along the path.
Credit: Burrus and Irvine/NIST
In the recent demonstration,* NIST's pair of laser frequency combs measured the simultaneous signatures of several greenhouse gases—including carbon dioxide, methane and water vapor—along a 2-kilometer path between a NIST laboratory roof in Boulder, Colo., and a nearby mesa.
Frequency combs are laser-generated tools made up of a large number of very precisely defined frequencies that are evenly spaced, like the teeth on a pocket comb. Each comb "tooth" represents an individual color, or frequency, enabling very accurate measurements of the characteristic absorption signatures of different gas molecules of interest.
Researchers identified gases in the atmosphere by measuring the amount of comb light absorbed at different frequencies during its trip from the NIST lab roof to a mirror on the mesa and back to a detector in a lab. Because the optical frequencies are too high to be measured directly, the researchers borrowed a trick from early radio. They created two combs with slightly different spacing between the teeth. Mixing light from these dual frequency combs together creates a "beat" frequency shifted down to the radio band, low enough to be measured. This was the first demonstration of the technique over long distances outdoors.
Remote sensing of atmospheric gases—from a satellite, for instance—can be performed with conventional instruments called spectrometers, but while satellite instruments have global coverage, they sample specific regions on Earth infrequently. Therefore, regional measurements are made with ground-based point sensors, which have a range that can be measured in meters and varies with wind conditions. There are no portable sensors that can measure multiple gases at long range with consistent results.
The NIST comb system was built to detect gases, including carbon dioxide, methane, and water over 2 kilometers. In principle, the dual-comb technique could detect an even wider range of gases over many kilometers. Accuracy in the measured atmospheric transmission is assured by the well-defined position of each frequency comb tooth.
Because the technique makes repeated measurements rapidly over the same path, it is immune to signal distortions caused by atmospheric turbulence. And because the comb measurements can be averaged over the entire path length rather than relying on a few spot measurements, the comb method is better matched to the scale of atmospheric transport models.
In the demonstration, the research team collected data continuously for three days under varied weather conditions. The results were comparable to data collected by a nearby point sensor under well-mixed atmospheric conditions. The comb measurements were also very precise—with uncertainty of less than 1 part per million for carbon dioxide, for example, obtained in five minutes. That's precise enough to ensure detection of small increases in trace gases due to large, distributed sources such as cities. Future systems should be able to achieve even better sensitivities over shorter timescales.
Overall, the study results suggest that the dual comb technique is ideally suited to precise, reproducible sensing of trace gases in the atmosphere and can support the development of accurate models for use in global, satellite-based greenhouse gas monitoring.
NIST researchers now plan to optimize the comb system by boosting power to improve sensitivity and expanding spectral coverage to identify additional gases. Portable frequency comb systems** could eventually support regional gas monitoring at costs comparable to point sensors, the researchers say, but over the kilometer scales relevant to many transport models and to monitoring of distributed sources such as large cities.
* G.B. Rieker, F.R. Giorgetta, W.C. Swann, J. Kofler, A.M. Zolot, L.C. Sinclair, E. Baumann, C. Cromer, G. Petron, C. Sweeney, P.P. Tans, I. Coddington and N.R. Newbury. Frequency comb-based remote sensing of greenhouse gases over kilometer air paths. Optica. Vol. 1, Issue 5. Posted online Oct. 29, 2014. DOI: 10.1364/OPTICA.1.000290.
** See "Portable Frequency Comb Rolls Out of the Lab" at http://www.nist.gov/pml/div686/sources_detectors/portable_frequency_comb.cfm
Laura Ost | EurekAlert!
Northern oceans pumped CO2 into the atmosphere
27.03.2017 | CAGE - Center for Arctic Gas Hydrate, Climate and Environment
Weather extremes: Humans likely influence giant airstreams
27.03.2017 | Potsdam-Institut für Klimafolgenforschung
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
27.03.2017 | Earth Sciences
27.03.2017 | Life Sciences
27.03.2017 | Life Sciences